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TOPS-20 DDT Manual
| Electronic distribution with Autopatch Tape 16
| August 1987
This manual describes the use
of TOPS-20 DDT, the Dynamic
Debugging Tool for MACRO-20
programs.
| This manual updates the
| TOPS-20 DDT Manual printed for
| TOPS-20 6.1. This version of
| the manual is not printed and
| is not available from DIGITAL
| in printed form. It is
| distributed on the Autopatch
| tape #16 for TOPS-20 in .MEM
| file format only. You can
| print this file on any
| printer; page length has been
| set at 58 lines. Change bars
| indicate changes and bullets
| indicate data deletions since
| the previous version of this
| manual.
OPERATING SYSTEM: TOPS-20 V6.1
| SOFTWARE: DDT V44C(670)
digital equipment corporation marlboro, massachusetts
First Printing, May 1985
| Autopatch Revision, August 1987
The information in this document is subject to change without notice
and should not be construed as a commitment by Digital Equipment
Corporation. Digital Equipment Corporation assumes no responsibility
for any errors that may appear in this document.
The software described in this document is furnished under a license
and may only be used or copied in accordance with the terms of such
license.
No responsibility is assumed for the use or reliability of software on
equipment that is not supplied by DIGITAL or its affiliated companies.
| Copyright (C) 1985, 1987, Digital Equipment Corporation.
All Rights Reserved.
The following are trademarks of Digital Equipment Corporation:
DEC DECnet IAS
DECUS DECsystem-10 MASSBUS
Digital Logo DECSYSTEM-20 PDT
PDP DECwriter RSTS
UNIBUS DIBOL RSX
VAX EduSystem VMS
VT
CONTENTS
PREFACE
CHAPTER 1 INTRODUCTION TO DDT
1.1 SYMBOLIC DEBUGGING . . . . . . . . . . . . . . . . 1-1
1.2 TOPS-20 VARIANTS OF DDT . . . . . . . . . . . . . 1-1
CHAPTER 2 GETTING STARTED WITH DDT
2.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . 2-1
2.2 LOADING DDT . . . . . . . . . . . . . . . . . . . 2-1
2.3 BASIC FUNCTIONS . . . . . . . . . . . . . . . . . 2-2
2.3.1 Error Conditions . . . . . . . . . . . . . . . . 2-3
2.3.2 Basic Concepts . . . . . . . . . . . . . . . . . 2-4
2.3.3 Starting and Stopping the Program . . . . . . . 2-5
2.3.4 Examining and Modifying Memory . . . . . . . . . 2-6
2.3.5 Executing Program Instructions . . . . . . . . . 2-9
2.4 A SAMPLE DEBUGGING SESSION USING DDT . . . . . . 2-10
2.5 PROGRAMMING WITH DDT IN MIND . . . . . . . . . . 2-21
CHAPTER 3 DDT COMMAND FORMAT
3.1 COMMAND SYNTAX . . . . . . . . . . . . . . . . . . 3-1
3.2 INPUT TO DDT . . . . . . . . . . . . . . . . . . . 3-2
3.2.1 Values in DDT Expressions . . . . . . . . . . . 3-2
3.2.2 Operators in DDT Expressions . . . . . . . . . . 3-7
CHAPTER 4 DISPLAYING AND MODIFYING MEMORY
4.1 DISPLAY MODES . . . . . . . . . . . . . . . . . . 4-1
4.1.1 Default Display Modes . . . . . . . . . . . . . 4-1
4.1.2 Selecting Display Modes . . . . . . . . . . . . 4-2
4.2 DISPLAYING EXPRESSIONS . . . . . . . . . . . . . . 4-6
4.3 DISPLAYING BYTE POINTERS . . . . . . . . . . . . . 4-6
4.4 DISPLAYING AND DEPOSITING IN MEMORY . . . . . . . 4-7
4.4.1 Commands that Use the Current Location . . . . 4-10
4.4.2 Commands that Use the Location Sequence Stack 4-11
4.4.3 Commands that Use an Address within the Command 4-12
4.5 DISPLAYING ASCIZ STRINGS . . . . . . . . . . . . 4-19
4.6 ZEROING MEMORY . . . . . . . . . . . . . . . . . 4-19
4.7 AUTOMATIC WRITE-ENABLE . . . . . . . . . . . . . 4-20
4.8 AUTOMATIC PAGE CREATION . . . . . . . . . . . . 4-21
4.9 DISPLAYING PAGE ACCESSIBILITY INFORMATION . . . 4-22
4.10 WATCHING A MEMORY LOCATION . . . . . . . . . . . 4-23
4.11 TTY CONTROL MASK . . . . . . . . . . . . . . . . 4-23
iii
CHAPTER 5 CONTROLLING PROGRAM EXECUTION
5.1 BEGINNING EXECUTION . . . . . . . . . . . . . . . 5-1
5.2 USING BREAKPOINTS . . . . . . . . . . . . . . . . 5-1
5.2.1 Setting Breakpoints . . . . . . . . . . . . . . 5-3
5.2.2 Proceeding from Breakpoints . . . . . . . . . . 5-6
5.2.3 Conditional Breakpoints . . . . . . . . . . . . 5-9
5.2.4 The "Unsolicited" Breakpoint . . . . . . . . . 5-10
5.3 EXECUTING EXPLICIT INSTRUCTIONS . . . . . . . . 5-11
5.4 SINGLE-STEPPING INSTRUCTIONS . . . . . . . . . . 5-11
5.5 EXECUTING SUBROUTINES AND RANGES OF INSTRUCTIONS 5-13
5.5.1 Single-Stepping "Dangerous" Instructions . . . 5-15
5.6 USER-PROGRAM CONTEXT . . . . . . . . . . . . . 5-16
CHAPTER 6 SEARCHING FOR DATA PATTERNS IN DDT
CHAPTER 7 MANIPULATING SYMBOLS IN DDT
7.1 OPENING AND CLOSING SYMBOL TABLES . . . . . . . . 7-1
7.2 DEFINING SYMBOLS . . . . . . . . . . . . . . . . . 7-2
7.3 SUPPRESSING SYMBOL TYPEOUT . . . . . . . . . . . . 7-3
7.4 KILLING SYMBOLS . . . . . . . . . . . . . . . . . 7-3
7.5 CREATING UNDEFINED SYMBOLS . . . . . . . . . . . . 7-4
7.6 FINDING WHERE A SYMBOL IS DEFINED . . . . . . . . 7-4
7.7 SEARCHING FOR SYMBOLS . . . . . . . . . . . . . . 7-5
7.8 LISTING UNDEFINED SYMBOLS . . . . . . . . . . . . 7-5
7.9 LISTING SYMBOLS . . . . . . . . . . . . . . . . . 7-5
7.10 LOCATING SYMBOL TABLES WITH PROGRAM DATA VECTORS . 7-6
CHAPTER 8 INSERTING PATCHES WITH DDT
CHAPTER 9 FILDDT
9.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . 9-1
9.2 USING FILDDT . . . . . . . . . . . . . . . . . . . 9-1
9.2.1 FILDDT Commands . . . . . . . . . . . . . . . . 9-3
9.2.2 Symbols . . . . . . . . . . . . . . . . . . . . 9-4
9.2.3 Commands to Establish Formats and Parameters . . 9-4
9.2.4 Commands to Access the Target and Enter DDT . . 9-5
9.2.5 Exiting FILDDT . . . . . . . . . . . . . . . . . 9-8
CHAPTER 10 PRIVILEGED MODES OF DDT
10.1 MDDT . . . . . . . . . . . . . . . . . . . . . . 10-2
10.2 KDDT . . . . . . . . . . . . . . . . . . . . . . 10-3
10.3 EDDT . . . . . . . . . . . . . . . . . . . . . . 10-4
iv
CHAPTER 11 PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
CHAPTER 12 EXTENDED ADDRESSING
12.1 LOADING DDT INTO AN EXTENDED SECTION . . . . . . 12-1
12.2 EXAMINING AND CHANGING MEMORY . . . . . . . . . 12-2
12.3 BREAKPOINTS . . . . . . . . . . . . . . . . . . 12-2
12.3.1 The Breakpoint Block . . . . . . . . . . . . . 12-2
12.3.2 Enabling and Disabling Inter-section
Breakpoints . . . . . . . . . . . . . . . . . 12-3
12.4 DISPLAYING SYMBOLS IN NONZERO SECTIONS . . . . . 12-4
12.5 DEFAULT SECTION NUMBERS . . . . . . . . . . . . 12-5
12.5.1 Permanent Default Section . . . . . . . . . . 12-6
12.5.2 Floating Default Section . . . . . . . . . . . 12-6
12.6 EXECUTING SINGLE INSTRUCTIONS . . . . . . . . . 12-8
12.7 ENTERING PATCHES IN EXTENDED SECTIONS . . . . . 12-8
APPENDIX A ERROR MESSAGES
GLOSSARY
INDEX
FIGURES
2-1 Sample Program X.MAC . . . . . . . . . . . . . . 2-11
2-2 Annotated Debugging Session . . . . . . . . . . 2-12
2-3 Terminal Display of Debugging Session . . . . . 2-20
4-1 DDT Session Showing Columnar Output . . . . . . 4-25
8-1 Annotated Patching Session . . . . . . . . . . . . 8-4
8-2 Terminal Display of Patching After an Instruction 8-5
8-3 Terminal Display of Patching Before an Instruction 8-6
TABLES
3-1 Commands that Return Values . . . . . . . . . . . 3-3
3-2 Effects of Operators When Evaluating Expressions . 3-8
4-1 Evaluation of Symbolic Display Mode . . . . . . . 4-1
4-2 DDT Display Modes . . . . . . . . . . . . . . . . 4-4
4-3 Commands to Display Expressions . . . . . . . . . 4-6
4-4 DDT Commands to Display Memory . . . . . . . . . . 4-9
4-5 TTY Control Mask . . . . . . . . . . . . . . . . 4-24
5-1 Breakpoint Locations of Interest . . . . . . . . . 5-2
5-2 User-Program Context Values . . . . . . . . . . 5-16
vi
PREFACE
MANUAL OBJECTIVES AND AUDIENCE
This manual explains and illustrates the features of TOPS-20 DDT, the
debugger for MACRO-20 programs. Although TOPS-20 DDT can be used to
debug the compiled code of programs written in higher-level languages,
this manual illustrates the use of TOPS-20 DDT to debug programs
written in MACRO-20 only.
This manual is both an introduction to the basic functions of TOPS-20
DDT and a reference guide to all TOPS-20 DDT commands and functions.
This manual assumes that the reader is familiar with using TOPS-20,
has done some programming in MACRO-20, and is familiar with the format
of MACRO-20 instructions.
STRUCTURE OF THIS DOCUMENT
This manual has 12 chapters, one appendix, and one glossary.
o Chapter 1 introduces the concept of symbolic debugging and
describes the variants of TOPS-20 DDT.
o Chapter 2 describes loading TOPS-20 DDT with your program,
discusses basic TOPS-20 DDT commands, and illustrates a
sample debugging session.
o Chapter 3 explains the syntax of a DDT command. Chapter 3
also describes expressions to enter data and explains how
TOPS-20 DDT evaluates expressions.
o Chapter 4 discusses how to examine and modify a program using
TOPS-20 DDT.
o Chapter 5 describes the use of TOPS-20 DDT to control program
execution: how to start, stop, and monitor the running of a
program.
vii
o Chapter 6 explains how to perform searches of a program's
address space using TOPS-20 DDT.
o Chapter 7 discusses the manipulation of program symbols using
TOPS-20 DDT.
o Chapter 8 describes how to use the TOPS-20 DDT patching
function to insert and test a new series of instructions in
your program without reassembling the program.
o Chapter 9 describes the use of FILDDT.
o Chapter 10 describes the use of the privileged DDTs: KDDT
and MDDT.
o Chapter 11 describes special-use commands that control
physical and virtual addressing. These commands are useful
primarily when running EDDT and FILDDT.
o Chapter 12 describes the use of DDT in non-zero sections
(NZS).
o Appendix A explains DDT and FILDDT error messages.
o The glossary defines important TOPS-20 DDT terms.
OTHER DOCUMENTS
Other documents to which the reader should have access are:
o MACRO Assembler Reference Manual
o TOPS-20 LINK Reference Manual
o TOPS-20 Commands Reference Manual
o DECsystem-10/DECSYSTEM-20 Processor Reference Manual
o TOPS-10/TOPS-20 RSX-20F System Reference Manual
viii
CONVENTIONS
The following conventions are used in this manual in the description
of DDT commands and concepts.
{} Curly brackets (braces) indicate that the enclosed item
is optional.
. (period) The address contained in DDT's location counter; also
called the current location.
addr A symbolic location within a program, a symbolic or
absolute address in memory, an AC, or ".", the current
location.
c A single ASCII or SIXBIT character.
expr Any expression that is legal in DDT.
filnam One or more components of a file specification.
instr Any instruction in the PDP-10 machine instruction set.
location sequence stack
A circular stack of memory locations that is used to
store the addresses of certain previously referenced
locations.
n A numeric argument.
page A page in memory. A page equals 512 words of memory.
symbol A symbol name of up to 6 RADIX50 characters.
text Any string of ASCII or SIXBIT characters.
word Any 36-bit value occupying one word of memory.
<ESC> Represents pressing the ESCAPE or ALTMODE key once.
<ESC><ESC> Represents pressing the ESCAPE or ALTMODE key twice.
<CTRL/X> Represents pressing a key (represented by X) at the
same time as you press the key labeled CTRL.
<BKSP> represents pressing the BACKSPACE key or <CTRL/H>.
<LF> Represents pressing the LINE FEED key.
<RET> Represents pressing the RETURN key.
<TAB> Represents pressing the TAB key or <CTRL/I>.
ix
Numbers are in octal radix unless otherwise specified.
Examples of interaction between the user and DDT show user input in
lowercase and DDT output in uppercase.
The symbols <BKSP>, <CTRL/x>, <ESC>, <LF>, <RET>, and <TAB> always
represent user input.
NOTE
The descriptions of many DDT commands list the actions
and effects of those commands. The actions and
effects may not occur in precisely the order
specified, but this has no effect on the user.
x
1-1
CHAPTER 1
INTRODUCTION TO DDT
DDT is a utility program you can use to help you debug your MACRO-20
programs. This manual describes how to use the DDT utility.
1.1 SYMBOLIC DEBUGGING
It is sometimes difficult to understand precisely the operation of a
program by reading the source code. DDT is a tool for interactively
examining the operation of a MACRO-20 program while it is running.
DDT is useful for finding programming errors (bugs) in programs that
do not run correctly. You can also use DDT to analyze the flow of
control in a program that is to be revised or rewritten.
With DDT, you can interrupt the execution of your program at locations
(breakpoints) you choose, and then examine and modify the program's
address space as required. You can execute instructions one-by-one to
check whether the effect of each instruction is what is intended. You
can then set other breakpoints in your program before continuing
execution.
When you refer to program locations and values, DDT allows you to use
the symbols that are defined in the program rather than absolute
values and addresses. This makes it much easier to refer to the
source listing and to find specific locations in memory.
After modifying the program's instructions or data, you can exit DDT
and save (with the monitor-level SAVE command) the changed version of
the program for further testing.
1.2 TOPS-20 VARIANTS OF DDT
There are several variants of DDT, each useful under specific
circumstances or for specific tasks.
1-1
INTRODUCTION TO DDT
The variants of TOPS-20 DDT are:
o EDDT
o FILDDT
o KDDT
o MDDT
o RDDT
o SDDT
o UDDT
o XDDT
EDDT is used to debug programs that run in executive mode (such as
BOOT), and is described in Chapter 10.
FILDDT is used to examine and patch disk files and structures. You
can also use FILDDT to examine the running monitor. FILDDT is
described in Chapter 9.
KDDT is used to debug and patch monitor .EXE files and the running
monitor, and is described in Chapter 10.
MDDT is used to debug and patch the running monitor, and is described
in Chapter 10.
RDDT is a relocatable variant of DDT that can be used to debug
programs in user mode. If your program is in memory (and has been
loaded with RDDT as below), you invoke RDDT by entering (at TOPS-20
command level):
START
You load RDDT with your program by running LINK as follows:
@LINK
*MYPROG,SYS:RDDT.REL/GO
where MYPROG is the name of your program. Loading RDDT.REL with your
program does not prevent you from using other LINK features. You must
load RDDT.REL last, or its start address is lost. RDDT.REL is useful
in situations where you do not wish to have DDT loaded at its default
location.
This example shows only the minimal steps required to load the
relocatable DDT with your program. See the LINK Reference Manual for
further information about using LINK.
1-2
INTRODUCTION TO DDT
SDDT is a "stub" that places XDDT in its own section, with system
symbols defined as in MONSYM and MACSYM. SDDT is the DDT variant
invoked when, at TOPS-20 command level, you enter:
SDDT
SDDT exists so that entering SDDT invokes DDT version 44 in the same
manner as previous versions.
UDDT is a "stub" that resides in your user program's section if the
program has a TOPS-10-style entry vector and the program entry vector
is in section zero. This is done for compatibility with programs that
use locations 770000, 770001 and 770002. If you load a program in
section zero and the program has a TOPS-10-style entry vector, when
you use the DDT command, the EXEC loads the UDDT stub into your
program's section at address 770000. UDDT then loads XDDT into the
highest-numbered free (nonexistent) section (if XDDT is not already
loaded), and starts XDDT.
XDDT is the DDT variant normally used to debug user programs. If you
load your program in a nonzero section or the program does not have a
TOPS-10-style entry vector, the DDT command causes the EXEC to load
XDDT directly into the highest-numbered free section. XDDT is also
invoked by the SDDT and UDDT stubs. If you type in XDDT while at
TOPS-20 command level, the EXEC loads XDDT into section zero, with
system symbols defined.
1-3
1-4
CHAPTER 2
GETTING STARTED WITH DDT
2.1 INTRODUCTION
This chapter is an introduction to using DDT. It describes how to
load DDT with your program and shows how to perform basic DDT
functions. It then illustrates a sample session debugging a simple
MACRO-20 program, using basic DDT functions. You can use DDT to debug
programs, using only the commands described in this chapter. Once you
are familiar with using these commands, you may wish to learn how to
use the commands and functions that are described in the rest of the
manual, to perform more sophisticated debugging.
The commands used in this chapter are described only in sufficient
detail for the debugging task being performed; all commands are
thoroughly described in Chapters 3 through 11 of this document.
The best way to learn is by doing. You will learn the commands and
techniques discussed in this manual if you use them as you read about
them. If you have a MACRO-20 program that you wish to debug, use it
to practice the commands discussed here. If not, type in the program
X.MAC listed in Figure 2-1.
2.2 LOADING DDT
| It is much easier to debug a program when you can use the symbols that
| are defined in the program. For you to be able to use program
| symbols, DDT must have access to your program's symbol table. One way
| to provide this access is to use the TOPS-20 DEBUG command to load DDT
| with your program and retain your program symbols. Load an existing
| MACRO-20 program with the TOPS-20 DEBUG command as follows:
|
| DEBUG filnam
|
2-1
GETTING STARTED WITH DDT
| where filnam is the name of your MACRO-20 program. The following
| appears on your terminal (if your .REL file is older than your .MAC
| file, MACRO-20 reassembles your program, otherwise the second line
| does not appear):
|
| @DEBUG PROG
| MACRO: filnam
| LINK: Loading
| [LNKDEB DDT execution]
| DDT
|
| where filnam is the name of your MACRO-20 program (with default
| extension .MAC). The last line (DDT) indicates that DDT is loaded,
| and is ready to accept your commands.
2.3 BASIC FUNCTIONS
You must be able to perform certain basic functions to interactively
debug a program. Basic DDT functions are:
o starting the program
o stopping the program at specified locations
o examining and modifying memory
o executing program instructions one-at-a-time
o continuing execution of the program
|
| o deleting input
o exiting DDT
You must give DDT commands to tell DDT what functions to perform. DDT
does not wait for a line terminator (such as a carriage return) to
indicate the end of your command. Instead, DDT reads your commands
character-by-character as you enter them. When you enter a DDT
command, you almost never have to press the RETURN key. This manual
explicitly indicates the occasions when a command requires you to
press the RETURN key.
NOTE
You must press the ESCAPE key as part of entering many
DDT commands. This manual uses the symbol <ESC> to
indicate where you press the ESCAPE key. When you
press the ESCAPE key, DDT displays a dollar sign ($)
on the screen. DDT never displays <ESC> when you
press the ESCAPE key.
2-2
GETTING STARTED WITH DDT
NOTE
This manual uses the symbols <BKSP>, <ESC>, <LF>,
<RET>, and <TAB> to indicate where you press the
BACKSPACE, ESCAPE, LINE FEED, RETURN, and TAB keys,
respectively. This manual also uses the symbol
<CTRL/X> to indicate where you simultaneously press
the CONTROL key and the key indicated by X. These
symbols ALWAYS indicate where you press the specific
keys noted here. You need NEVER enter the characters
<BKSP>, <ESC>, <LF>, <RET>, <TAB>, or <CTRL/X>, to
enter a DDT command.
Your commands appear on the screen as you type them. Use the DELETE
key to delete partially entered commands character-by-character. If
you try to delete more characters than you have entered, DDT displays:
XXX
You can delete an entire command line with <CTRL/U>. When you do, DDT
displays:
XXX
To exit DDT, enter:
<CTRL/Z>
The other basic DDT functions are described in the rest of this
chapter.
2.3.1 Error Conditions
If DDT cannot execute a command, it displays a message to let you
know. The message may be only a single character (such as M or U, for
Multiply-defined symbol or Undefined symbol), a question mark (?), or
a complete message string. For most errors, DDT also sets a pointer
to the error string, so that if DDT did not display it, you can enter
a command to display the error string. The error string is available
for display until another error occurs, when DDT changes the pointer.
To display the error string that describes the last DDT error, enter:
<ESC>?
(press the ESCAPE key, followed by a question mark).
o
2-3
GETTING STARTED WITH DDT
2.3.2 Basic Concepts
A very useful DDT concept is that of the current location. The
current location is a memory location that you have referenced, either
implicitly or explicitly, with your last command, and that is the
default point of reference of your next command. The current location
can be thought of as the location "where you are". The symbol "."
(period) refers to the address of the current location, and can be
used as an argument in DDT commands.
The location counter is a DDT pointer that contains the address of the
current location. The location counter performs a function similar to
that of a bookmark. You can enter a command to display the contents
of a specific location but not change the address of the current
location, in order to maintain a specific point of reference for your
next command. Most DDT commands change the address of the current
location, and therefore also change the location counter. The
commands that do not change the current location are so indicated.
The open location is a memory word that can be modified by your next
command. DDT "opens" the location as a result of a command you give
to examine or modify memory. There is never more than one location
open at any given time. The open location is usually also the current
location.
To find the symbolic address of the current location, enter:
._ (a period followed by an underscore)
This causes DDT to display the following:
ADDR1+n
where ADDR1 is a label defined in your program, and n is the offset of
the current location from that label (if the current location is
ADDR1, DDT does not display +n).
Another useful DDT concept is that of the current quantity. This is a
value that is the contents of the last word that DDT displayed, or the
value that you last deposited in memory. The current quantity is the
most recent of those values. Many DDT commands use arguments that
default to the current quantity.
The location sequence stack is a DDT storage area used to store the
addresses of previous current locations. Certain DDT commands store
the address of the current location on the location sequence stack.
Other DDT commands change the address of the current location to an
address that has already been stored on the location sequence stack.
The location sequence stack functions in a fashion similar to
inserting place-markers in a source code listing, to be able to "get
back" to prior references.
2-4
GETTING STARTED WITH DDT
2.3.3 Starting and Stopping the Program
When your program is loaded and DDT is ready to accept your commands
(as indicated by DDT appearing on the terminal display), you can begin
execution of your program at its start address by entering:
<ESC>G
Unless you set one or more breakpoints before you start the program,
your program runs either to completion or until it commits a fatal
error. A breakpoint is a location in a program's executable code that
has been modified so that if the program attempts to execute the
instruction at that location, control passes to DDT before the
instruction is executed.
The command to set a breakpoint is:
addr<ESC>B
where addr is the address at which to stop execution. If the
user-program PC reaches addr, DDT interrupts execution of the program
before the program executes the instruction at the specified address.
When DDT interrupts program execution at a breakpoint, it changes the
current location to the breakpoint and opens the current location (the
breakpoint).
While program execution is stopped at a breakpoint, you can display
and change the contents of instruction and data words, remove
breakpoints, set new breakpoints, and execute instructions one at a
time (single-step). As you examine memory, you may find an
instruction that is incorrect, and modify it. You can also examine
and modify data words in memory. After modifying incorrect
instructions and data in memory, you can immediately execute the
instructions to check the effects of the modifications, without having
to reassemble the source code.
Once you have made your changes, you can continue program execution at
the place where execution was interrupted, restart the program at the
beginning, or start execution at any other location you choose. The
program will run to completion, until it reaches a breakpoint, or
until it gets a fatal error.
2-5
GETTING STARTED WITH DDT
2.3.4 Examining and Modifying Memory
One command to examine memory is:
addr/
where addr is the address of the memory word you wish to examine
(display), and can be numeric or symbolic. DDT displays the contents
of the word located at addr. If the opcode field (bits 0-8) of the
memory word matches a recognized instruction or user-defined OPDEF,
DDT displays the contents of addr as an instruction (or OPDEF). If
DDT finds (in the symbol table) any of the values to be displayed, DDT
displays those symbols rather than the numeric values. For example,
either of the following display lines might appear on your terminal
(depending on the address and contents of the word):
ADDR1/ MOVE 2,SYM1
ADDR1+5/ SYM1,,SYM2
where ADDR1, SYM1, and SYM2 have been defined in the program.
If you enter a symbol that DDT does not find in the symbol table, DDT
sounds the terminal buzzer or bell, and displays U on the screen. If
you enter a symbol that is defined as a local symbol in more than one
module, DDT sounds the terminal buzzer or bell and displays M. You
can eliminate the multiply-defined symbol problem by "opening" the
symbol table of the module in which the correct symbol is defined.
See Chapter 7 (Manipulating Symbols in DDT) for more information.
When searching for a symbol to display, DDT uses global symbols in
preference to local symbols. However, DDT searches the "open" symbol
table first, and treats local symbols found in the open symbol table
as global symbols. If DDT finds only a local symbol that is not in
the open symbol table, DDT displays the symbol with a pound-sign (#)
appended to the symbol. For example, DDT might display:
ADDR#/ MOVE 2,SYM1#
See Chapter 7 (Manipulating Symbols in DDT) for more information on
symbols and symbol tables.
The command addr/ changes the current location to addr and opens the
word at addr.
If you omit addr from an examine-memory command, such as addr/, DDT
uses the current quantity to determine the address of the location to
display. For example, after DDT displays the contents of ADDR1+5 as
above, if you enter "/", DDT displays the contents of the word located
at SYM2. The display line then appears:
ADDR1+5/ SYM1,,SYM2 / value
2-6
GETTING STARTED WITH DDT
where value is the contents of the word located at SYM2. By default,
DDT displays value symbolically if it can.
The command / by itself (without addr) does not change the current
location. Both forms of the / command open the location displayed,
enabling you to modify the location with your next command.
Another very useful command for examining memory is <TAB>. This
| command starts a new display line before displaying the contents of
| addr, making the display easier to read. For example, if you enter
<TAB> after DDT displays the address and contents of ADDR1+5 (as
above) on your terminal, the terminal display appears:
ADDR1+5/ SYM1,,SYM2 <TAB>
SYM2/ value
where value is the contents of the word located at SYM2. <TAB> does
not appear on the screen, but is shown above to indicate where you
| press the <TAB> key. <TAB> changes the current location to SYM2 and
| opens the word at SYM2. In this example, the current quantity becomes
| value.
<TAB> also stores the address of the current location (ADDR1+5) on the
location sequence stack before changing the current location to the
location just displayed (SYM2). DDT uses the location sequence stack
to "remember" previous values of the location counter. To "get back"
to the previous current location, enter:
<ESC><RET>
In the above example, after you press <TAB> at ADDR1+5, DDT displays
the contents of SYM2 and changes the current location to SYM2. When
you enter <ESC><RET>, DDT changes the current location to ADDR1+5,
opens the location at ADDR1+5, and again displays the contents of
ADDR1+5.
o
If you use the command addr<TAB>, DDT deposits addr in the open
location and closes the location before opening the location at addr
and displaying its contents. <TAB> by itself does not deposit
anything, but does save the current location on the location sequence
stack, making <TAB> more useful than / (slash by itself).
You can display and open the word after the current location by
entering:
<LF>
2-7
GETTING STARTED WITH DDT
DDT changes the current location to the next word in memory, starts a
new line, and displays the address of the (new) current location (as a
symbol or a symbol plus an offset, if it can find a corresponding
symbol in the symbol table), displays the contents of the current
location, and opens the current location. For example, to display the
next word in memory after ADDR1+5, enter:
<LF>
DDT changes the current location to ADDR1+6, starts a new line, and
displays the address and contents of ADDR1+6. The screen display then
appears as follows:
ADDR1+5/ SYM1,,SYM2 <LF>
ADDR1+6/ -1,,SYM3
Note that DDT does not display the characters <LF>. <LF> does not
affect the location sequence stack.
Entering another <LF> causes DDT to display and open the next word.
To display and open the word previous to the current location, enter:
<BKSP>
DDT changes the current location to the previous word, starts a new
line, displays the address and contents of the (new) current location,
and opens the current location. <BKSP> does not affect the location
sequence stack. For example, if you enter <BKSP> to open and display
the location before ADDR1+5, the screen appears as follows:
ADDR1+5/ SYM1,,SYM2 <BKSP>
ADDR1+4/ -3,,SYM2
Note that <BKSP> does not appear on the screen.
To change the contents of the open location, enter:
value<RET>
where value can be an instruction, a symbol, or a numeric expression.
For example, if you enter the command LABL2/, DDT displays the
contents of the memory word at LABL2, and "opens" that word. If the
word at LABL2 contains:
MOVE 1,SYM1
and you wish to change SYM1 to SYM2, enter:
MOVE 1,SYM2<RET>
2-8
GETTING STARTED WITH DDT
DDT stores the new instruction in the location at LABL2 and "closes"
the location. DDT does NOT display <RET>. The terminal display
appears as follows (your input is in lowercase):
labl2/ MOVE 1,SYM1 move 1,sym2<RET>
The current location is still LABL2, but there is no open location.
To check whether the instruction is now correct, you can enter:
./
to display the contents of the current location. The screen display
now appears (your input is in lowercase):
labl2/ MOVE 1,SYM1 move 1,sym2<RET>
./ MOVE 1,SYM2
After entering a command to display and open a location, if you enter:
value<LF>
DDT stores the new value, changes the current location to the next
location in memory, starts a new display line and opens and displays
the new current location. The example above would then appear as
follows (your input is in lowercase):
labl2/ MOVE 1,SYM1 move 1,sym2<LF>
LABL2+1/ CONTENTS
where CONTENTS is the value stored at LABL2+1.
o
2.3.5 Executing Program Instructions
When you have interrupted program execution at a breakpoint, you can
execute the next instruction (the one at the breakpoint), by entering:
<ESC>X
DDT executes the instruction, displays the results of executing the
instruction, and displays the address and contents of the next
instruction to be executed. This command changes the current location
to the next instruction to be executed. For example, assume that the
next instruction to be executed is located at LABEL1, which contains:
MOVE 1,VARIBL
2-9
GETTING STARTED WITH DDT
If the word at VARIBL contains SYM1, when you enter <ESC>X, DDT starts
a new line and displays:
1/ SYM1 VARIBL/ SYM1
LABEL1+1/ instr
where instr is the contents of LABEL1+1, and is the next instruction
to be executed. You can continue to execute instructions
one-at-a-time by entering successive <ESC>X commands. This is known
as single-stepping.
To execute a subroutine, enter:
<ESC><ESC>X
| DDT executes the subroutine and returns control to you if the
| subroutine returns to a location +1, +2, or +3 from the instruction
| that calls the subroutine. DDT changes the current location to the
| address of the next instruction to be executed.
o
To continue execution of the program until the next breakpoint or
until program completion, enter:
<ESC>P
DDT starts the program running again, beginning with the next
instruction to be executed. If you did not single-step any
instructions, the program begins by executing the instruction at the
breakpoint. If you have executed any instructions by single-stepping,
the program continues where you stopped. The effect is as if the
program were running without DDT in control.
o
2.4 A SAMPLE DEBUGGING SESSION USING DDT
This section describes a debugging session using DDT. The program
being debugged is X.MAC, shown in Figure 2-1. The program and the
sample session are for illustration only. There are many styles of
programming and debugging, and these examples are descriptive rather
than prescriptive in intent.
You will understand this section and learn the commands described more
easily if you type in the program listed in Figure 2-1 and use the
commands as they are described.
2-10
GETTING STARTED WITH DDT
Figure 2-1: Sample Program X.MAC
SEARCH MONSYM
TITLE X
R0=0 ;AC0
IDX=6 ;INDEX REGISTER
P=17 ;STACK COUNTER
START:: MOVE P,PWORD ;Set up stack counter
MOVEI IDX,TABLE1 ;Address of table with X & Y
PUSHJ P,ADDEM ;Do the addition
MOVEI IDX,TABLE1 ;Address of table
MOVE R0,ANSWER(IDX) ;Answer to R0
JFCL 0
HALTF% ;All done!
ADDEM: MOVE R0,X(IDX) ;Load X
ADD R0,Y(IDX) ;X + Y
MOVE R0,ANSWER(IDX) ;Store answer
POPJ P, ;Return
TABLE1: BLOCK 3 ;3 words
X==0 ;Offset for X
Y==1 ;Offset for Y
ANSWER==2 ;Offset for answer
STKSIZ==10 ;Stack size
PWORD: IOWD STKSIZ,STACK ;Stack pointer
STACK: BLOCK STKSIZ ;Stack
END START
Figure 2-2 is an annotated session debugging X.MAC, the program in
Figure 2-1. In the annotated session, the DDT terminal display is on
the left, user input is in the center in lowercase, and explanatory
comments about the session are on the right. This is not always the
way it appears on the terminal. Figure 2-3 shows the session as it
actually appears on the terminal.
The program is designed to pass the address of a table to a
subroutine. The table contains three elements. The subroutine is to
add the first two elements of the table and store the result in the
third element before returning to the main program. There are no
input or output routines in the program. The table is initialized
using DDT, and the result is checked while in DDT.
NOTE
DDT does not display <LF>, <RET>, or <TAB>. These are
shown in the sample session to indicate user input.
2-11
GETTING STARTED WITH DDT
NOTE
DDT does not display the AC field of an instruction if
it is zero. This means that if your program contains
the instruction MOVE R0,LABL1, where R0=0, DDT
displays the instruction as MOVE LABL1.
Figure 2-2: Annotated Debugging Session
SCREEN DISPLAY USER INPUT EXPLANATION
@ TOPS-20 prompt.
debug x<RET> Begin the session by entering
"debug x<RET>", where x is the
name of your MACRO program.
MACRO: X MACRO reassembles your program
LINK: Loading (if needed), and LINK loads
[LNKDEB DDT execution] your program with DDT. DDT
DDT displays the "DDT" prompt.
start/ Begin examining code at
label "START".
MOVE P,PWORD# DDT displays the instruction
at START.
<LF> Press <LF> to display the next
instruction.
.JBDA+1/ MOVEI IDX,TABLE1# The first symbol in this
program happens to coincide
with .JBDA, a JOBDAT symbol.
When DDT scans the symbol
table, it finds .JBDA before
it finds START, and displays
.JBDA instead. DDT still
accepts START as an input
symbol.
Also note the pound-sign (#)
appended to TABLE1 and
PWORD. PWORD and TABLE1 are
local symbols that are not
in the open symbol table.
2-12
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
.jbda<ESC>k Enter .jbda<ESC>k
to suppress DDT typeout of
symbol .JBDA. DDT will
display START rather than
.JBDA from now on.
x<ESC>: Enter the module name (X)
followed by <ESC> and a
colon to open the symbol
table associated with
X. DDT will not append any
more pound-signs.
<TAB> Press <TAB> to start a new
display line, evaluate the
current quantity as if it
were an instruction, and
display the contents of the
location addressed by the Y
field of the instruction.
(Entering / (slash) displays
the same word as <TAB>, but
does not start a new line.)
<TAB> also saves your place
(like a bookmark) on the
location sequence stack, so
you can get back here easily.
TABLE1/ 0 When you enter the <TAB>
command, DDT displays the
address and the contents of
the location. The first
element of the table contains
zero. The <TAB> command also
opens the location.
2<LF> Enter "2" followed by <LF> to
deposit the value "2" in the
first element, and to open and
display the second element.
TABLE1+1/ 0 The second element contains
zero.
2-13
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
3<LF> Enter "3" followed by <LF> to
deposit the value "3" in the
second element and open and
display the third element.
The addition to be performed
by the program is 2+3.
TABLE1+2/ 0 The third element (the answer)
contains zero.
<ESC><RET> Press <ESC>, then press <RET>
to return to the address you
saved on the location sequence
stack.
START+1/ MOVEI IDX,TABLE1 DDT displays the address and
contents of the last location
you displayed before you
entered <TAB>.
<LF> Press <LF> to look at the
next location.
START+2/ PUSHJ P,ADDEM This is the call to the
subroutine that does the
computation.
.<ESC>b Enter ".", press <ESC>, and
enter "b" to set a
breakpoint at the current
location.
<ESC>g Enter <ESC>g to start
program execution.
$1B>>START+2/ PUSHJ P,ADDEM DDT displays the breakpoint
number, the address of the
breakpoint, and the
instruction at the breakpoint.
This instruction has not yet
been executed.
<ESC><ESC>x Press <ESC> twice, then
enter "x" to let DDT
execute the subroutine.
2-14
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
START+3/ MOVEI IDX,TABLE1 DDT returns from the
subroutine at the next
instruction, and displays the
address and contents of the
instruction. If there is a
"skip return", DDT displays
"<SKIP>" if the program
skipped one instruction. If
the program skips 2 or 3
instructions, DDT displays
"<SKIP n>", where n is the
number of instructions
skipped.
<ESC>x Press <ESC> and enter "x"
to execute the instruction.
IDX/ TABLE1 TABLE1 DDT displays the address and
contents of IDX (the result of
executing the instruction),
and also displays "TABLE1"
(the result of evaluating the
Y field of the instruction).
START+4/ MOVE 2(IDX) DDT then starts a new line and
displays the address and
contents of the next
instruction. Note that
DDT does not display the
zero in the AC field of
the instruction.
<ESC><TAB> Press <ESC>, then <TAB> to
display the contents of the
location addressed by the
instruction, using any
indexing and indirection.
(If you omit <ESC>, DDT uses
only the Y field, without
indexing and indirection.)
TABLE1+2/ 0 The location addressed by the
instruction is TABLE1+2, and
its contents is zero. This is
the table element that
contains the answer, which
should be 5.
2-15
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
<BKSP> Press <BKSP> to see the
previous element in the table.
TABLE1+1/ 3 This element contains 3. That
is correct.
<BKSP> Press <BKSP> again to check
the previous element.
TABLE1/ 2 This element contains 2. That
is also correct. One way to
find the error is to
single-step through the
program.
start<ESC>b Enter "start", press <ESC>,
and enter "b" to set a
breakpoint at the beginning of
the program.
<ESC>g Press <ESC> and enter "g" to
start the program again.
$2B>>START/ MOVE P,PWORD DDT displays the breakpoint
number, and the address and
contents of the instruction
at the breakpoint.
<ESC>x Press <ESC>, then enter "x" to
execute the instruction. This
instruction moves a memory
word to a register.
P/ -10,,PWORD PWORD/ -10,,PWORD
DDT displays the address and
new contents of the register,
and the address and contents
of the memory word.
START+1/ MOVEI IDX,TABLE1 DDT then displays the address
and contents of the next
instruction.
2-16
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
<ESC>x Press <ESC>, then enter "x" to
execute this instruction,
which moves an immediate value
to a register.
IDX/ TABLE1 TABLE1 DDT displays the address and
new contents of the register,
and the immediate value.
START+2/ PUSHJ P,ADDEM DDT then displays the address
and contents of the next
instruction.
<ESC>x Press <ESC>, then enter "x"
to execute the instruction.
P/ -7,,STACK DDT displays the address and
new contents of the stack
pointer used by the PUSHJ.
<JUMP> DDT displays "<JUMP>" if the
change in PC is less than one
or greater than 4.
ADDEM/ MOVE 0(IDX) DDT displays the address and
contents of the next
instruction to be executed.
<ESC>x Press <ESC> and enter "x" to
execute the instruction.
0/ 2 TABLE1/ 2 The instruction moved the
contents of the word at
TABLE1 (which is 2) to AC0.
Looks OK so far.
ADDEM+1/ ADD 1(IDX) DDT displays the next
instruction.
<ESC>x Press <ESC> and enter "x"
to execute the instruction.
0/ 5 TABLE1+1/ 3 The instruction added the
contents of the word at
TABLE1+1 (which is 3) to AC0,
which now contains 5. OK.
2-17
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
ADDEM+2/ MOVE 2(IDX) DDT displays the next
instruction.
<ESC>x Press <ESC> and enter "x"
to execute the instruction.
0/ 0 TABLE1+2/ 0 The instruction moved the
contents of the word at
TABLE1+2 to AC0. The MOVE
instruction at ADDEM+2 should
be MOVEM.
ADDEM+3/ POPJ P,0 DDT displays the next
instruction (as a result of
the <ESC>x).
<BKSP> Press <BKSP> to display and
open the location with the
incorrect instruction.
ADDEM+2/ MOVE 2(IDX) DDT displays the previous
instruction. This is the
incorrect instruction.
movem r0,answer(idx)<RET>
Enter the new instruction
and press <RET>.
./ Check the current location
to see what you deposited.
MOVEM 2(IDX) Looks OK.
.<ESC>b Set a breakpoint at
".", the current location.
<ESC>g Restart the program at
the beginning.
$2B>>START/ MOVE P,PWORD DDT displays the breakpoint
information.
<ESC>p Press <ESC> and enter "p" to
proceed from breakpoint 2
to the next breakpoint.
2-18
GETTING STARTED WITH DDT
Figure 2-2: Annotated Debugging Session (Cont.)
SCREEN DISPLAY USER INPUT EXPLANATION
$1B>>START+2/ PUSHJ P,ADDEM DDT displays the breakpoint
information.
<ESC>p Proceed from breakpoint 1.
$3B>>ADDEM+2/ MOVEM 2(IDX) DDT displays the breakpoint
information. This is the
instruction you changed.
<ESC>x Single-step the instruction
to watch what it does.
0/ 5 TABLE1+2/ 5 The instruction moves the
contents of AC0 to the word
at TABLE1+2. OK!!
ADDEM+3/ POPJ P,0 DDT also displays the address
and contents of the next
instruction.
start+4<ESC>b Set a breakpoint at
START+4 to check the results.
<ESC>p Proceed from breakpoint 3.
$4B>>START+4/ MOVE 2(IDX) DDT displays the breakpoint
information.
<ESC>x Single-step the instruction.
0/ 5 TABLE1+2/ 5 The instruction moves the
contents of the word at
TABLE1+2 to AC0. The new
value of AC0 is 5. OK!
START+5/ JFCL 0 DDT displays the address and
contents of the next
instruction.
<CTRL/Z> Quit.
@ Back at TOPS-20 command level.
2-19
GETTING STARTED WITH DDT
Figure 2-3 shows the session as it actually appears on the terminal
screen. Again, user input is in lowercase. Comments on the right
indicate where you enter characters that do not echo.
Figure 2-3: Terminal Display of Debugging Session
@debug x
MACRO: X
LINK: Loading
[LNKDEB DDT execution]
DDT
start/ MOVE P,PWORD# Enter <LF>.
.JBDA+1/ MOVEI IDX,TABLE1# .jbda$k x$: Enter <TAB>.
TABLE1/ 0 2 Enter <LF>.
TABLE1+1/ 0 3 Enter <LF>.
TABLE1+2/ 0 $ Enter <ESC><RET>.
START+1/ MOVEI IDX,TABLE1 Enter <LF>.
START+2/ PUSHJ P,ADDEM .$b $g
$1B>>START+2/ PUSHJ P,ADDEM $$x
START+3/ MOVEI IDX,TABLE1 $x
IDX/ TABLE1 TABLE1
START+4/ MOVE 2(IDX) $ Enter <ESC><TAB>.
TABLE1+2/ 0 Enter <BKSP>.
TABLE1+1/ 3 Enter <BKSP>.
TABLE1/ 2 start$b $g
$2B>>START/ MOVE P,PWORD $x
P/ -10,,PWORD PWORD/ -10,,PWORD
START+1/ MOVEI IDX,TABLE1 $x
IDX/ TABLE1 TABLE1
START+2/ PUSHJ P,ADDEM $x
P/ -7,,STACK
<JUMP>
ADDEM/ MOVE 0(IDX) $x
0/ 2 TABLE1/ 2
ADDEM+1/ ADD 1(IDX) $x
0/ 5 TABLE1+1/ 3
ADDEM+2/ MOVE 2(IDX) $x
0/ 0 TABLE1+2/ 0
ADDEM+3/ POPJ P,0 Enter <BKSP>.
ADDEM+2/ MOVE 2(IDX) movem r0,answer(idx) Enter <RET>.
./ MOVEM 2(IDX) .$b $g
$2B>>START/ MOVE P,PWORD $p
$1B>>START+2/ PUSHJ P,ADDEM $p
$3B>>ADDEM+2/ MOVEM 2(IDX) $x
0/ 5 TABLE1+2/ 5
ADDEM+3/ POPJ P,0 start+4$b $p
$4B>>START+4/ MOVE 2(IDX) $x
0/ 5 TABLE1+2/ 5
START+5/ JFCL 0 ^Z
@
2-20
GETTING STARTED WITH DDT
2.5 PROGRAMMING WITH DDT IN MIND
There are a few MACRO-20 programming techniques that make debugging
with DDT easier. These techniques primarily concern the use of labels
and symbols.
Labels that meaningfully describe (perhaps mnemonically) the function
of the code are more helpful when examining code and setting
breakpoints than labels that are alphanumerically coded (such as
A0001).
When using symbols as offsets into tables, you can prevent DDT from
displaying the offset symbol in place of the symbol's numeric value if
you define the symbol in this way:
symbol==expression
Symbol is still entered in the symbol table, and you can use symbol as
input to DDT, but DDT does not display symbol on output.
For example, if you have defined:
OFFSET==3
DDT displays the contents of a word that contains the value of 3 as:
addr/ 3
rather than:
addr/ OFFSET
where addr is the address of the word. See the MACRO Assembler
Reference Manual for more information about defining symbols.
2-21
2-22
CHAPTER 3
DDT COMMAND FORMAT
3.1 COMMAND SYNTAX
The complete syntax of a DDT command is:
{arg1<}{arg2>}{arg3}{<ESC>{<ESC>}{arg4}}c{arg5}
where arg1, arg2, arg3, arg4, and arg5 are arguments to the command c.
Arg1, arg2, and arg3 can be any legal DDT expression. Arg1 must be
followed by a left angle bracket (<), and arg2 must be followed by a
right angle bracket (>). Arg4 can only be a number. Arg5 is a text
argument of the form:
/text/ or c<ESC>
where text is a string of characters, the slashes (/) are delimiters
that can be any character not contained in text, and c is a single
character.
DDT commands never use all five arguments. Each argument is optional
or required according to the syntax of the specific command. Most DDT
commands are not more complicated than:
arg3<ESC>c or arg3<ESC>arg4c
You can enter alphabetic commands and text arguments in uppercase or
lowercase.
An argument to a command can be the result of executing another
command. For example, you can enter a command to evaluate a text
string, and then enter another command to deposit in memory the result
of evaluating the text string. The entire command line would be:
"/abcd/<RET>
where /abcd/ is the argument to the command " (quotation mark). The
function of the quotation mark command is to evaluate the string
(abcd) within the delimiters (/) as a left-justified ASCII string.
3-1
DDT COMMAND FORMAT
The left-justified ASCII string abcd is then the argument to the
command <RET> (entered by pressing the RETURN key). The function of
the <RET> command is to deposit an argument (in this case, the string
abcd) into the open location. The " command is described in this
chapter, and the <RET> command is described in Chapter 4 (Displaying
and Modifying Memory).
Most commands produce results that are immediately visible, such as
commands that display the contents of memory locations. However,
commands such as those that invoke search functions or those that
evaluate text expressions (as above) may not produce immediately
visible results. If you enter a question mark (?) while DDT is
performing a function invoked by one of these commands, DDT displays a
message that tells you what DDT is currently doing. For example, such
a message might be:
Searching: addr/ value
where addr is the address that DDT is to next test as part of a
search, and value is the contents of the memory location at addr.
Still other commands return values that DDT does not display, but can
use as arguments to other commands.
3.2 INPUT TO DDT
You enter arguments to DDT as expressions. An expression can be a
single value, or a combination of two or more values with one or more
operators.
3.2.1 Values in DDT Expressions
Values in DDT expressions can be:
o octal or decimal integers
o floating point numbers
o symbols
o values that are returned by commands
o text
To enter an octal integer value, simply enter the integer in octal
digits. For example:
70707065
3-2
DDT COMMAND FORMAT
To enter a decimal integer value, enter the integer in decimal digits
and follow the value with a decimal point. For example:
9876.
To enter a floating point number, use regular or scientific notation.
For example, you can enter the value .034 as one of the following:
.034
3.4E-2
Note that 1. is a decimal integer, while 1.0 is a floating point
number.
To enter a symbol as a value in an expression, type in the symbol name
as defined in your program. To enter an undefined symbol that you can
define later, enter:
symbol#
where symbol is the symbol that you will later define. See Chapter 7
(Manipulating Symbols in DDT) for more information about using
undefined symbols.
You can enter a command that returns a value as a value in an
expression. DDT commands that return values and the values they
return are listed in Table 3-1.
Table 3-1: Commands that Return Values
COMMAND VALUE RETURNED VALUE ALSO
KNOWN AS
. The address of the current location. .
<ESC>. The address of the next user program $.
instruction to be executed.
<ESC><ESC>. The previous value of "<ESC>.". $$.
<ESC>nB The address of the DDT location that $nB
contains the address of breakpoint n.
<ESC>nI The address of the DDT location that
contains the saved machine state flags
(user-program context).
<ESC>nM The address of DDT "mask" n.
<ESC>Q The current quantity. $Q
3-3
DDT COMMAND FORMAT
Table 3-1: Commands that Return Values (Cont.)
COMMAND VALUE RETURNED VALUE ALSO
KNOWN AS
<ESC><ESC>Q The current quantity, with halves $$Q
swapped.
<ESC>nU The address of the DDT location that
contains the argument (or default) that
was given in the virtual addressing
command: expr<ESC>nU.
The commands <ESC>nB, <ESC>nI, <ESC>nM, and <ESC>nU, return values that
are the addresses of locations internal to DDT, which contain
information that you can use and modify. For brevity, these commands
are said to address those internal DDT locations.
For example, the command <ESC>nB returns (but does not display) the
address of the DDT location that contains the address of breakpoint n,
and the command addr/ (address followed by slash) displays the contents
of the location at addr. To display the address of breakpoint n, enter:
<ESC>nB/
where you enter the command <ESC>nB as the expression for DDT to
evaluate as addr.
| You can enter text to be interpreted in the following ways:
|
| o left-justified ASCII strings
|
| o left-justified SIXBIT strings
|
| o single right-justified ASCII characters
|
| o single right-justified SIXBIT characters
|
| o RADIX50 words
|
You can enter text expressions in uppercase or lowercase. DDT
translates strings to uppercase for SIXBIT or RADIX50 text as required.
The term long text string refers to an expression in a DDT command that
is a string of text characters that requires more than one 36-bit
expression for full evaluation. You can enter long text strings in
SIXBIT and ASCII as DDT expressions. If you use a long text string as
an expression, DDT assumes that you will enter a command that deposits
the expression in memory.
3-4
DDT COMMAND FORMAT
DDT evaluates the string one 36-bit expression at a time. After
evaluating the first 36-bit expression, DDT deposits the expression in
the open location, closes the open location, and opens the next
location.
DDT then evaluates the next 36-bit expression contained in the string,
and deposits that expression in the (new) open location. This process
continues until you enter c, the command. If you enter a command that
does deposit to memory, DDT deposits the final 36-bit expression in the
open location, and updates the location counter according to the rules
of that particular command. The current quantity is the last 36-bit
expression that DDT evaluated.
If you do not enter a command that deposits to memory, DDT uses, as the
argument to the command, the 36-bit expression that was last evaluated.
All other 36-bit expressions that were evaluated as part of the string
have been deposited, and the current and open locations were updated
accordingly. The current quantity is then the last 36-bit expression
that DDT evaluated.
If there is no open location when you begin typing the long text string,
DDT evaluates only the first 36-bit expression, ignores the rest of the
string, and uses the first 36-bit expression as the argument to the
command. The current quantity is then the first 36-bit expression that
DDT evaluated in the string. If you enter a command that deposits to
memory, it has no effect because there was no open location.
o
The syntax to enter an ASCII string is:
"/text/
where text is the string, and the slashes (/) represent any printing
character that is not contained within text. DDT evaluates the string
as a series of 36-bit expressions, each in 7-bit ASCII format
(left-justified), with all unused bits reset.
For example, if you enter:
"+abc/def+
DDT evaluates one 36-bit expression as the 7-bit ASCII string abc/d in
bits 0-34, and bit 35 reset. If there is no open location, DDT uses
that expression as the argument to the command, and that expression
becomes the current quantity.
If there is an open location, DDT deposits abc/d in the open location,
closes it, and opens the next location in memory. DDT then evaluates a
second 36-bit expression as the 7-bit ASCII string ef in bits 0-13, and
bits 14-35 reset. The last 36-bit expression evaluated becomes the
current quantity.
3-5
DDT COMMAND FORMAT
NOTE
You cannot use this format to enter an ASCII string that
begins with the ESCAPE character, because <ESC>
terminates the command that enters a single
right-justified ASCII character (in this case, your
intended delimiter).
The syntax to enter a SIXBIT string is:
<ESC>"/text/
where text is the string, and the slashes (/) represent any printing
character that is not contained within text. DDT evaluates the string
as a series of 36-bit expressions, each in SIXBIT format
(left-justified), with any unused bits in the last 36-bit expression
reset. DDT translates lowercase characters to uppercase; all other
non-SIXBIT characters cause DDT to sound your terminal buzzer or bell
and display a question mark.
For example, if you enter:
<ESC>"/qwertyu/
DDT evaluates one 36-bit expression as the SIXBIT string QWERTY in bits
0-35. If there is no open location, DDT uses that expression as the
argument to the command, and that expression becomes the current
quantity.
If there is an open location, DDT deposits QWERTY in the open location,
closes it, and opens the next location in memory. DDT then evaluates a
second 36-bit expression as the SIXBIT character U in bits 0-5, with
bits 6-35 reset. The last 36-bit expression evaluated becomes the
current quantity.
The syntax to enter a right-justified ASCII character is:
"c<ESC>
where c is the character. DDT evaluates this as one 36-bit expression
with the 7-bit ASCII character c in bits 29-35, and bits 0-28 reset.
3-6
DDT COMMAND FORMAT
The syntax to enter a right-justified SIXBIT character is:
<ESC>"c<ESC>
where c is the character. DDT evaluates one 36-bit expression with the
SIXBIT character c in bits 30-35, and bits 0-29 reset. DDT translates
lowercase characters to uppercase; all other non-SIXBIT characters cause
DDT to sound your terminal buzzer or bell and display a question mark.
The syntax to enter a RADIX50 word is:
text<ESC>5"
where text is any string of RADIX50 characters up to six characters
long. DDT evaluates one 36-bit expression with bits 0-3 reset and the
RADIX50 string text in bits 4-35. DDT ignores any characters in text
after the sixth.
For example, if you enter:
poiuytr<ESC>5"
DDT evaluates one 36-bit expression with bits 0-3 reset and the RADIX50
string POIUYT in bits 4-35. DDT ignores the character r. DDT
translates lowercase characters to uppercase. Characters in text not in
the RADIX50 character set that are DDT commands use, as an argument to
the command, any characters already entered. Characters in text not in
the RADIX50 character set that are not DDT commands cause DDT to sound
your terminal buzzer or bell and display a question mark.
3.2.2 Operators in DDT Expressions
When you enter an expression, DDT evaluates the expression to create a
36-bit quantity but does not necessarily use all 36 bits when it
executes the command. For example, you can enter a complete MACRO
instruction when giving an argument to a command that requires an
address, but DDT uses only the address specified by the instruction (and
ignores the rest of the evaluated expression) when it executes the
command.
Table 3-2 lists DDT's expression operators and the effects those
operators produce on the evaluation. The term value so far represents
the accumulated 36-bit value resulting from evaluation of the expression
to that point.
3-7
DDT COMMAND FORMAT
Table 3-2: Effects of Operators When Evaluating Expressions
OPERATOR EFFECT ON EVALUATION
+ Add the 36-bit value on the left to the 36-bit
value on the right, using two's complement
addition.
- Subtract the 36-bit value on the right from the
36-bit value on the left, using two's complement
subtraction.
* Multiply the 36-bit value on the left by the
36-bit value on the right, using PDP-10
full-word integer multiplication. DDT uses only
the low-order 36 bits of the result.
' (apostrophe) Divide the 36-bit value on the left by the
36-bit value on the right, using PDP-10
full-word integer division. DDT ignores any
remainder.
NOTE
Apostrophe is DDT's division
operator. / (slash) is a DDT command
to examine memory, and is never used
in DDT to indicate division.
space Add the previous expression (normally an opcode)
to the value so far, and add the low-order 18
bits of the value at the right of the space to
the low-order 18 bits of the value so far. DDT
ignores carries resulting from the addition, and
does not change the left half of the value so
far.
3-8
DDT COMMAND FORMAT
Table 3-2: Effects of Operators When Evaluating Expressions (Cont.)
OPERATOR EFFECT ON EVALUATION
, (comma) If you are entering an I/O instruction, shift
the low-order 18 bits of the expression at the
left of the comma 26 bits to the left (to the
device field of the instruction), otherwise
shift the low-order 18 bits of the expression at
the left of the comma 23 bits to the left (to
the A field of an instruction). Then logically
OR the result into the value so far.
NOTE
DDT does not check whether the value
at the left of the comma is a
legitimate device or AC address, and
may overwrite other parts of the
instruction.
() Swap the halves of the expression within the
parentheses and add the resulting expression to
the value so far. This makes it possible to
enter an instruction that uses an index
register.
NOTE
DDT does not check whether the value
within the parentheses is a
legitimate AC address, and may
overwrite other parts of the
instruction.
@ Assume the expression is an instruction and set
the indirect bit (bit 13) of the value so far.
,, (two commas) Move the low-order bits of the expression at the
left of the commas to bits 0-17 and build a new
18-bit expression in the right half.
3-9
DDT COMMAND FORMAT
The nonarithmetic operators allow you to enter expressions in
instruction format as well as in data format.
To enter an instruction, format the instruction as you would in a
MACRO-20 program. For example:
MOVE R4,@VAR1+OFFSET(R5)
NOTE
Follow an opcode (such as MOVE) with a space, not a
<TAB>.
To enter halfwords, enter the values (numbers or symbols) separated by
two commas (,,). The halfwords can be symbolic or absolute values. For
example:
-1,,SYM1
NOTE
DDT is not designed to evaluate complicated arithmetic
expressions. The nonarithmetic operators are
implemented to enable DDT to evaluate expressions you
enter as MACRO-20 instructions and halfwords. Using
values and operators for other purposes may not produce
the results you intend.
3-10
CHAPTER 4
DISPLAYING AND MODIFYING MEMORY
4.1 DISPLAY MODES
A major function of DDT is displaying the contents of memory words, both
data and instructions. You can choose whether to display the contents
of memory words as symbols or as numeric values. You can also select
the radix in which DDT displays numeric values.
DDT displays symbols, labels, and most messages in uppercase.
4.1.1 Default Display Modes
There is no sure way for DDT to distinguish between instruction and data
words, or between data words of different formats.
DDT displays memory words in symbolic mode by default. Symbolic mode is
described in Table 4-1. DDT tests for the condition on the left, and if
the condition is met, displays the word in the format described on the
right. DDT performs the tests in descending order.
Table 4-1: Evaluation of Symbolic Display Mode
CONDITION DDT DISPLAYS EXAMPLE
Bits 0-18 are all set. A negative number -45
in the current
radix.
The 36-bit value is defined The symbol. SYMBL1
in the user program symbol HALT
table.
The opcode field is zero. Halfwords. 345,,-27
4-1
DISPLAYING AND MODIFYING MEMORY
Table 4-1: Evaluation of Symbolic Display Mode (Cont.)
CONDITION DDT DISPLAYS EXAMPLE
The opcode and I, X, and Y The OPDEF. CORE 6,
fields, or the opcode and A
fields match an OPDEF in the
user program symbol table.
The opcode matches a The instruction. MOVE 3,SYMBL
definition in DDT's internal
hardware instruction table.
No match. Halfwords. 3445,,-23
By default, DDT displays numeric values in radix 8. Leading zeros are
always suppressed.
4.1.2 Selecting Display Modes
You can select display modes to control:
o the format in which DDT tries to interpret the contents of memory
locations; for example, as instructions, or as floating-point
numbers.
o whether addresses are displayed as symbolic or numeric values.
o the radix in which numeric values are displayed.
In addition, you can specify these modes on a short-term (temporary mode)
or long-term (prevailing mode) basis.
A prevailing display mode remains in effect until you select another
prevailing mode, but may be overridden by a temporary mode until you enter
a command that restores the prevailing display mode. DDT commands that
restore the prevailing display mode are:
o {expr}<RET> (deposit expr and close location)
o <ESC>G (start program execution)
o <ESC>P (proceed from a breakpoint)
o <ESC>W, <ESC>E, <ESC>N (perform a search)
o <ESC>Z (zero memory)
4-2
DISPLAYING AND MODIFYING MEMORY
o instr<ESC>X (execute instr)
o <ESC>V (watch a location)
The syntax of commands that set the prevailing mode is:
<ESC><ESC>mode
where mode is one of the display modes shown in Table 4-2.
The syntax of commands that set a temporary mode is:
<ESC>mode
where mode is one of the display modes shown in Table 4-2.
The current display mode is the mode (prevailing or temporary) in which
DDT will display the next word (unless you enter a command to change the
display mode).
DDT has two "masks" that control the action of two of the display modes.
<ESC>3M is a command that addresses a DDT location that contains the
output byte size mask. When the current display mode is O, each bit that
is set in the mask indicates the position of a low order bit of a byte in
the word being displayed. In this mode, bit 35 is always assumed to be
set. For example, if the output byte size mask contains:
510410100400 (octal)
the byte sizes specified are, from left to right, 1, 2, 3, 4, 5, 6, 7, and
8. When displaying a word in O mode that contains 777777,,777777, and the
current radix is 8, DDT displays:
1,3,7,17,37,77,177,377
The default value of the output byte size mask is zero, specifying one
36-bit byte.
You can set the output byte size mask with the command:
expr<ESC>3M
where expr evaluates to the bit pattern required.
You can also examine and change the output byte size mask with the examine
and deposit commands described later in this chapter.
4-3
DISPLAYING AND MODIFYING MEMORY
<ESC>2M is a command that addresses a DDT location that contains the
maximum symbolic offset. When DDT displays an address in R(elative) mode,
it displays the address symbolically, that is, as a symbol, or as a symbol
+ the numeric offset of the address from that symbol. The maximum
symbolic offset (minus 1) determines the maximum offset address that DDT
displays symbolically, and defaults to 1000 (octal). DDT displays
addresses beyond that offset in A(bsolute) mode. For example, assume that
the maximum symbolic offset is 2, and that you are examining subroutine
ADDEM in program X.MAC (Fig 2-1), using <LF> to display instructions in
sequence. DDT displays:
ADDEM/ MOVE 0(6)
ADDEM+1/ ADD 1(6)
addr/ MOVE 2(6)
where addr is the absolute address (for example, 14414) of the location.
You can set the maximum symbolic offset with the command:
expr<ESC>2M
where expr evaluates to the offset required.
You can also examine and change the maximum symbolic offset with the
examine and deposit commands described later in this chapter.
DDT display modes and the commands that select them are described in Table
4-2.
Table 4-2: DDT Display Modes
FORMAT MODES
MODE EFFECT
C Display memory word as numbers in the current radix (see
Radix Modes).
F Display memory word as a floating point decimal number.
H Display memory word as two halfword addresses (see
Address Modes) separated by two commas (,,).
O Display memory word as numeric bytes of sizes that are
specified by the <ESC>3M mask.
n0 Display memory word as n-bit numeric bytes, (with
trailing remainder byte, as required).
4-4
DISPLAYING AND MODIFYING MEMORY
Table 4-2: DDT Display Modes (Cont.)
FORMAT MODES
MODE EFFECT
S Display memory word in symbolic mode (default).
1S Search DDT's internal hardware opcode table before
searching the user's symbol table, otherwise follow
rules for symbolic mode.
nT Display memory word as ASCII text, using n-bit bytes.
| n=1: Byte Pointer Format
n=5: RADIX50
n=6: SIXBIT
| n=7 through 36:
|
| Specifies the number of bits per byte. The
| default is 7-bit ASCII.
|
| n=0: ASCIZ
|
| (Stop ASCIZ typeout by typing any character.)
A Display addresses as absolute values in the current
radix.
R Display addresses as values relative to symbols
(default). DDT displays the offsets in the current
radix. The maximum offset is controlled by the value
stored in the <ESC>2M mask, and defaults to 1000
(octal).
RADIX MODES
MODE EFFECT
nR Display numeric values in radix n (default=8), where n
is a decimal number greater than 1. If n=8, DDT
displays the word as octal halfwords, otherwise DDT
displays the word as one number.
o
4-5
DISPLAYING AND MODIFYING MEMORY
4.2 DISPLAYING EXPRESSIONS
DDT has three commands you can use to display expressions in different
modes. They are:
; (semicolon)
= (equal sign)
_ (underscore)
The syntax of these commands is:
{expr}c
where expr is the expression to display (expr defaults to the current
quantity), and c is one of the above commands. These commands are
useful for redisplaying the current quantity without affecting the
current display mode. Table 4-3 lists the commands to display
expressions and their effects.
Table 4-3: Commands to Display Expressions
COMMAND EFFECT
; Display the current quantity in the current display
mode.
expr; Display expr in the current display mode.
= Display the current quantity as a number in the
current radix.
expr= Display expr as a number in the current radix.
- Display the current quantity in 1$ mode.
expr_ Display expr in 1$ mode.
4.3 DISPLAYING BYTE POINTERS
If you set the display mode to 1T, DDT displays the contents of the
memory location as a byte pointer. DDT can display one-word local,
one-word global, and two-word byte pointers. DDT displays the P and S
fields, and the address as determined by the I, X, and Y fields of the
byte pointer.
In section zero, DDT displays only one-word byte pointers (local and
global).
4-6
DISPLAYING AND MODIFYING MEMORY
For example, if the contents of the location at ADDR2 is 100702,,addr,
where addr is the value of symbol LABL2, the following illustrates
one-word local byte pointer display:
addr2/ 100702,,addr <ESC>lT; 10 7 LABL2(2)
The following illustrates one-word global byte pointer display, where
addr is the value of symbol LABL2:
1,,addr2/ 610002,,LABL2 <ESC>lT; 44&7 2,,LABL2
The following illustrates two-word global byte pointer display, where
addr is the value of symbol LABL2 (DDT echoes <BKSP> as ^H):
1,,addr2/ 440740,,0 <LF>
1,,addr2+1/ 3,,addr <ESC>lT^H
1,,addr2/ 44 7 3,,MAIN. <2>
4.4 DISPLAYING AND DEPOSITING IN MEMORY
DDT allows you to display the contents of memory locations and deposit
a new value in the open location. In performing these functions, you
must understand the concept of the open location, the current
location, the location sequence stack, and the current quantity.
The open location is a memory location (or AC) that is "open" for
modification by the next command. There is never more than one
location open at a time. DDT always closes the open location before
opening another.
The location counter contains the address of a word in memory that has
been referenced (implicitly or explicitly) by the previous command,
and that is the default point of reference for the next command. That
word is known as the current location. DDT uses the address of the
current location as the default address in most commands. The current
location is often, but not always, the open location.
Most DDT commands change the current location to a word specified by
an address given (explicitly or by default) in the command. Commands
that do not are so indicated.
"." (period) is a command that returns (but does not display) the
address of the current location.
When you first enter DDT, the current location is zero.
4-7
DISPLAYING AND MODIFYING MEMORY
The location sequence stack is a "ring" of seventeen words, each
containing the address of a prior current location, or of a match
found during a search. The present value of the current location is
not placed in the ring.
Entries are made to and retrieved from the location sequence stack in
a last-in, first-out manner. Most commands that change the location
counter by values other than +1 and -1 cause DDT to place the address
of the current location (before the change) on the location sequence
stack. Addresses of matching locations found during searches are also
placed on the location sequence stack. When DDT enters a new value in
the next word on the stack, the new value becomes the current location
stack entry. This is similar to PUSHing entries on a stack. When the
current location stack entry is the last location on the location
sequence stack, DDT enters a new value on the stack by "wrapping
around" to the beginning of the stack and overwriting the value in the
first location on the stack. The first location on the stack then
contains the current location stack entry.
Certain DDT commands change the address of the current location to the
current location stack entry, and then change the current location
stack entry to the previous entry. This is similar to POPing entries
off a stack, and allows you to "return" to locations that have
previously been the current location. When the first location on the
location sequence stack contains the current location stack entry and
DDT changes the address of the current location to the current
location stack entry, DDT "wraps around" to the end of the stack, and
the value contained in the last word of the stack becomes the current
location stack entry (whether or not the stack was previously "full").
The current quantity is a value that is the most recent of:
o the last 36-bit quantity that DDT displayed (an expression or
the contents of a memory location)
o the last expression that you entered as an argument to a
command that deposits to memory
This value is also known as the last value typed. <ESC>Q is a command
that returns (but does not display) the current quantity. DDT issues
an implicit <ESC>Q to return this value for use as the default
argument for some commands.
You can give the current quantity as an argument to a command by
entering the command <ESC>Q as the argument.
The command <ESC><ESC>Q returns the current quantity with the right
and left halves swapped.
This manual uses the term $Q to refer to the value that is returned by
the command <ESC>Q, and the term $$Q to refer to the value that is
returned by the command <ESC><ESC>Q.
4-8
DISPLAYING AND MODIFYING MEMORY
Some commands calculate the address of the location to be opened from
an expression given or defaulted in the command. Other commands use
the address of the current location or entries on the location
sequence stack.
The general syntax of these commands is:
{expr}{<ESC>}c
where expr is any legal DDT expression, and c is the command.
NOTE
See Values in DDT Expressions in Chapter 3 for a
discussion of long text strings as values in DDT
expressions.
Table 4-4 summarizes the commands and their effects. Complete
descriptions of the commands follow the table.
Table 4-4: DDT Commands to Display Memory
COMMAND DISPLAY MODE OPEN CHANGE DEPOSIT
CONTENTS OF THE CURRENT EXPR
DISPLAY LOCATION LOCATION
/ Yes Current Yes Yes(1) No
[ Yes Numeric Yes Yes(1) No
] Yes Symbolic Yes Yes(1) No
! No Suppress Yes Yes(1) No
\ Yes(2) Current Yes No Yes(1)
<TAB> Yes(2) Current Yes Yes Yes(1)
<RET> No Restore No No Yes(1)
<LF> Yes(2) Current Yes Yes(.+1) Yes(1)
<BKSP> Yes(2) Current Yes Yes(.-1) Yes(1)
or ^
(1) If you enter expr.
(2) If not suppressed by !.
4-9
DISPLAYING AND MODIFYING MEMORY
4.4.1 Commands that Use the Current Location
The commands <RET>, <LF>, and <BKSP> use the address of the current
location to determine the next address of the current location.
These commands do not make entries to the location sequence stack.
{expr}<RET> does the following:
o deposits expr (if given) in the open location
o closes the open location
o resets the current typeout mode to the prevailing typeout
mode
o does not change the address of the current location
{expr}<LF> does the following:
o deposits expr (if given) in the open location
o closes the open location
o increments the location counter
o opens the current location
o
o displays the open location (unless display has been
suppressed by !)
{expr}<BKSP> and {expr}^ do the following:
o deposits expr (if given) in the open location
o closes the open location
o decrements the location counter
o opens the current location
o
o displays the open location (unless display has been
suppressed by !)
4-10
DISPLAYING AND MODIFYING MEMORY
4.4.2 Commands that Use the Location Sequence Stack
The commands <ESC><RET>, <ESC><LF>, and <ESC><BKSP> use the current
location stack entry to determine the next address of the current
location.
Repetitions of these commands refer to successively earlier entries on
the stack, until you again address the most recent entry.
These commands do not make entries to the location sequence stack.
{expr}<ESC><RET> does the following:
o deposits expr (if given) in the open location
o closes the open location
o changes the value contained in the location counter to the
current location stack entry
o opens the current location
o starts a new line and displays the address and contents of
the open location in the current display mode
o causes the previous entry on the location sequence stack to
become the current location stack entry
NOTE
If display is suppressed as a result of using the !
command, the command {expr}<ESC><RET> restores the
current display mode, which can be either a temporary
or prevailing display mode.
{expr}<ESC><LF> does the following:
o deposits expr (if given) in the open location
o closes the open location
o changes the value contained in the location counter to the
current location stack entry
o increments the location counter
o opens the current location
o starts a new line and displays the address of the open
location
4-11
DISPLAYING AND MODIFYING MEMORY
o displays the contents of the open location (unless display
has been suppressed by !)
o causes the previous entry on the location sequence stack to
become the current location stack entry
{expr}<ESC><BKSP> and {expr}<ESC>^ do the following:
o deposits expr (if given) in the open location
o closes the open location
o changes the value contained in the location counter to the
current location stack entry
o decrements the location counter
o opens the current location
o displays the address of the open location
o
o displays the contents of the open location (unless display
has been suppressed by !)
o causes the previous entry on the location sequence stack to
become the current location stack entry
4.4.3 Commands that Use an Address within the Command
The commands:
/ (slash)
[ (left square bracket)
] (right square bracket)
! (exclamation point)
\ (backslash)
<TAB>
use an expression given in the command (either explicitly or by
default) to determine the addresses of the current location and the
open location.
4-12
DISPLAYING AND MODIFYING MEMORY
The complete syntax of these commands is:
{expr}{<ESC>{<ESC>}}c
where expr may be an address, ".", a symbol, or any expression that is
legal in DDT, and c is the command.
When you use the commands /, [, ], !, \, and <TAB>:
o If you omit expr
> DDT uses the current quantity as a default.
> <TAB> enters the address of the current location on the
location sequence stack and changes the current location
to the address determined from the current quantity.
o If you enter expr, DDT enters the address of the current
location on the location sequence stack (except \).
o DDT treats expr (whether given or defaulted) as if it were in
instruction format and performs the effective address
calculation as follows:
> If you omit <ESC>, DDT does not perform indexing or
indirection.
> If you include one <ESC>, DDT treats expr as an IFIW
(instruction format indirect word), and uses the I and Y
fields of expr to perform indexing and indirection when
appropriate.
> If you use <ESC><ESC>, DDT utilizes EFIWs (extended
format indirect words), as appropriate, when performing
effective address calculations, and can thereby calculate
30-bit addresses.
> In section zero, when you include <ESC><ESC>, it is
treated as one <ESC>.
These commands always do the following:
o close the open location
o open the location at the address indicated by expr
o change the current quantity to the value displayed (all
commands except !)
4-13
DISPLAYING AND MODIFYING MEMORY
The following is a list that gives a complete description of the
effects of each command.
COMMAND EFFECTS
/
o closes the open location
o opens the location at the address calculated from the current
quantity
o displays the contents of the open location in the current
display mode
o sets the current quantity to the value displayed
expr/
o closes the open location
o opens the location at the address calculated from expr
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from expr
o displays the contents of the open location in the current
display mode
o sets the current quantity to the value displayed
[
o closes the open location
o opens the location at the address calculated from the current
quantity
o displays the contents of the open location in numeric mode in
the current radix
o
o sets the current quantity to the value displayed
4-14
DISPLAYING AND MODIFYING MEMORY
expr[
o closes the open location
o opens the location at the address calculated from expr
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from expr
o displays the contents of the open location in numeric mode in
the current radix
o sets the current display mode to numeric mode in the current
radix
o sets the current quantity to the value displayed
]
o closes the open location
o opens the location at the address calculated from the current
quantity
o displays the contents of the open location in symbolic mode
o sets the current display mode to symbolic mode
o sets the current quantity to the value displayed
expr]
o closes the open location
o opens the location at the address calculated from expr
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from expr
o displays the contents of the open location in symbolic mode
o sets the current display mode to symbolic mode
o sets the current quantity to the value displayed
4-15
DISPLAYING AND MODIFYING MEMORY
!
o closes the open location
o opens the location at the address calculated from the current
quantity
o does not display the contents of the open location
o suppresses display of the open location by the \, <TAB>,
<LF>, and <BKSP> commands (any other display command restores
the current display mode)
o does not change the current quantity
expr!
o closes the open location
o opens the location at the address calculated from expr
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from expr
o does not display the contents of the open location
o suppresses display of the open location by the \, <TAB>,
<LF>, and <BKSP> commands (any other display command restores
the current display mode)
o does not change the current quantity
\
o closes the open location
o opens the location at the address calculated from the current
quantity
o displays the contents of the open location in the current
display mode (unless display has been suppressed by !)
o sets the current quantity to the value displayed
4-16
DISPLAYING AND MODIFYING MEMORY
expr\
o deposits expr in the open location
o closes the open location
o opens the location at the address calculated from expr
o does not change the address of the current location (and does
not enter the address of the current location on the location
sequence stack)
o displays the contents of the open location in the current
display mode (unless display has been suppressed by !)
o sets the current quantity to the value displayed
<TAB>
o closes the open location
o opens the location at the address calculated from the current
quantity
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from the current quantity
o starts a new line and displays the address of the open
location (which is also the current location)
o displays the contents of the open location in the current
display mode (unless display has been suppressed by !)
o sets the current quantity to the value displayed
expr<TAB>
o deposits expr in the open location
o closes the open location
o opens the location at the address calculated from expr
o enters the address of the current location on the location
sequence stack
o changes the current location to the location at the address
calculated from expr
4-17
DISPLAYING AND MODIFYING MEMORY
o starts a new line and displays the address of the open
location (which is also the current location)
o displays the contents of the open location in the current
display mode (unless display has been suppressed by !)
o sets the current quantity to the value displayed
You can treat expr as an IFIW (instruction format indirect word), and
use any indexing and indirection specified by expr to compute the
effective address of the location to be opened. Use the command form:
{expr}<ESC>c
where c is /, [, ], !, \, or <TAB>.
For example, assume the following conditions as indicated by the
display commands:
COMMAND DISPLAY EXPLANATION
LABL1/ SYM1 Display contents of LABL1.
LABL1+1/ SYM2 Display contents of LABL1+1.
SYM2/ SYM3 Display contents of SYM2.
2/ 1 Display contents of AC 2.
@LABL1(2)/ SYM1 DDT uses Y field only.
@LABL1(2)<ESC>/ SYM3 <ESC> causes indexing and indirection.
Note that DDT does not start a new line unless you enter <TAB>, <RET>,
<LF> or <BKSP>, or until the display wraps around the end of the line.
DDT also displays three spaces (or a tab, depending on the TTY control
mask) before and after its output. Thus, an actual DDT terminal
display might be the following (user input is lowercase; <LF> and
<TAB> do not appear on the screen, but are shown to indicate where you
pressed the corresponding keys):
2/ 1 labl1/ SYM1 <LF>
LABL1+1/ SYM2 <TAB>
SYM2/ SYM3 sym4/ MOVE 1,@LABL1(2) <ESC><TAB>
SYM2/ SYM3
You can treat expr as an EFIW (extended format indirect word) and use
any indexing and indirection specified by expr to compute the (global)
effective address of the location to be opened. Use the command form:
{expr}<ESC><ESC>c
where c is /, [, ], !, \, or <TAB>.
4-18
DISPLAYING AND MODIFYING MEMORY
4.5 DISPLAYING ASCIZ STRINGS
You can display memory as an ASCIZ string. The command
addr<ESC>0T
where addr defaults to the open location (if there is one, otherwise
addr defaults to the current location), displays memory, beginning
with addr, as an ASCIZ string. The display stops when DDT finds a
zero byte, or when you type in any character, which DDT displays, but
otherwise ignores. The current location remains unchanged.
4.6 ZEROING MEMORY
To deposit the same value in each of a string of memory words (useful
for initializing memory to zero), enter:
addr1<addr2>{expr}<ESC>Z
where expr is any legal DDT expression, addr1 is the first word to
receive expr, and addr2 is the last. Follow addr1 with a left angle
bracket (<) and addr2 with a right angle bracket (>). Both addr1 and
addr2 are required. If you omit expr, it defaults to zero. Prior to
execution, DDT enters the address of the current location on the
location sequence stack and closes the open location. When DDT has
| completed execution of the command, the current location is the word
| at addr2 + 1. There is no open location. This command restores the
prevailing display mode.
If you enter:
?
while DDT is executing the <ESC>Z command, DDT displays:
Depositing: addr/ value
where addr is the location where DDT will make the next deposit, and
value is the contents of addr before the deposit.
If you enter any other character, DDT stops executing the <ESC>Z
| command, and waits for your next command. The character that you
| enter to terminate the <ESC>Z command is otherwise ignored.
4-19
DISPLAYING AND MODIFYING MEMORY
4.7 AUTOMATIC WRITE-ENABLE
If you attempt to deposit a value in a location that is
write-protected, DDT returns the message
?NOT WRITABLE
This is the TOPS-20 default condition.
To allow DDT to modify write-protected memory, type in
<ESC>{0}W
If you now attempt to deposit a value in a location that is
write-protected, DDT removes the protection, deposits the value, and
then reinvokes the protection.
Note that you cannot use this command to enable patching in FILDDT.
To prevent DDT from modifying write-protected memory, type in
<ESC><ESC>{0}W
The zero in the above commands is optional and has no effect on the
operation of the commands. DDT allows the zero for compatibility with
prior versions of DDT.
4-20
DISPLAYING AND MODIFYING MEMORY
4.8 AUTOMATIC PAGE CREATION
If you attempt to deposit a value in a location within a nonexistent
page, DDT creates the page and deposits the value. If you attempt to
deposit a value within a nonexistent section, DDT creates the section
as well as the page. This is the default condition.
To prevent DDT from creating a page when you attempt to deposit a
value within a nonexistent page, type in
<ESC><ESC>1W
If you now attempt to deposit a value in a location within a
nonexistent page, DDT returns the error message
CAN'T CREATE PAGE
To allow DDT to create the page (and the section, as required) when
you attempt to deposit a value within a nonexistent page, type in
<ESC>1W
4-21
DISPLAYING AND MODIFYING MEMORY
| 4.9 DISPLAYING PAGE ACCESSIBILITY INFORMATION
|
| You can get information about the access requirements of the pages and
| sections in the program you are debugging, using the $L and $$L
| commands. The complete format for this command is:
{{arg1<}arg2}{<ESC>}<ESC>L
where arg1 and arg2 are section numbers. Using one <ESC> causes DDT
to display access information about the section and about individual
pages. Using <ESC> twice causes DDT to display access information
only about the section(s). If you include both arg1 and arg2, DDT
displays the information for all sections that your program and DDT
are using, in the range arg1 to arg2, inclusive. If you include only
arg2, DDT displays access information for that section only. If you
omit both arguments, DDT displays access information for all sections
that your program and DDT are using.
The page and section accessibility bits and their meanings are:
Read Page can be read.
Write Page can be written.
Copy-on-write Page is copy-on-write
Execute page can be executed
Private page is private
Zero Page is allocated but zero.(FILDDT only)
For example, the command <ESC>L might produce the following display:
| Section 0 Read, Write, Execute, Private
| 000 Read, Write, Execute, Private
| 770 Read, Execute
| 771 Read, Write, Execute, Private
| Section 37 Read, Write, Execute, Private
| 700-701 Read, Copy-on-write, Execute
| 703-730 Read, Copy-on-write, Execute
| 735-736 Read, Write, Execute, Private
| 740-753 Read, Execute
And the command <ESC><ESC>L might produce a display like the
following:
Section 0 Read, Write, Execute, Private
Section 37 Read, Write, Execute, Private
4-22
DISPLAYING AND MODIFYING MEMORY
4.10 WATCHING A MEMORY LOCATION
If you wish to have DDT monitor or "watch" a memory location while
your program is running, and display the location whenever its
contents change, enter:
addr<ESC>V
where addr is the address of the location to be watched, and defaults
to the current location. When you enter the command, DDT starts a new
line and displays:
addr/ value
where addr is the address of the location being watched, and value is
the contents of the location. This command also restores the
prevailing display mode.
DDT checks addr every "jiffy" (about 20 milliseconds), and displays
the address and contents of addr whenever those contents change.
(Executive mode EDDT watches addr continuously.)
If you enter a question mark (?) while DDT is watching, DDT displays:
Watching: addr/ value
where addr is the address of the location being watched, and value is
the contents of addr.
To terminate the watch, enter any other character. DDT stops
monitoring the word, starts a new display line, echoes the character
you enter, starts another line, and waits for more input. The
character that you enter to terminate the watch is otherwise ignored.
Because any input character terminates the watch, you cannot continue
execution and watch your own user program. The <ESC>V command is
useful to watch activity in a separate process (such as the running
monitor or other job, for which you must be using EDDT or FILDDT).
The page that contains the word you wish to watch must be mapped into
your own process (the one that contains DDT and your program).
4.11 TTY CONTROL MASK
You can control certain aspects of DDT's display by setting DDT's TTY
control mask. The command <ESC>1M returns a value that is the address
of the DDT location that contains this mask. Table 4-5 summarizes the
features controlled by the bits in the TTY control mask.
4-23
DISPLAYING AND MODIFYING MEMORY
Table 4-5: TTY Control Mask
BIT VALUE EXPLANATION
15 0 Display the commands (and results) from the file
executed by the <ESC>Y command (default).
1 Do not display the commands (or results) from the
file executed by the <ESC>Y command.
16 0 When interrupting program execution at a
breakpoint, display the address and contents of
the breakpoint (default).
1 When interrupting program execution at a
breakpoint, display only the address of the
breakpoint.
17 0 Display 3 spaces when spacing DDT output (1).
1 Display DDT output fields at tab stops (1).
34 0 The terminal does not have a tab mechanism (2).
1 The terminal has a tab mechanism (2).
35 0 Echo deleted characters (3).
1 Backspace over deleted characters (3).
(1) If bit 17 is reset (default), DDT displays 3 spaces between
output fields (such as between the address of a location and the
contents of the location), and at the end of display lines. If
bit 17 is set, DDT lines up the output fields in columns
beginning at tab stops (see bit 34). Figure 4-1 illustrates the
two different modes.
(2) If bit 34 is set, DDT displays a tab character (<CTRL/I>)
between fields. If bit 34 is reset, DDT displays enough spaces
to start the field at the next tab stop. When starting up, DDT
checks whether your terminal can handle TAB characters
(<CTRL/I>), and sets this bit accordingly.
(3) When starting up, DDT checks whether your terminal can
backspace to delete characters, and sets this bit accordingly.
4-24
DISPLAYING AND MODIFYING MEMORY
To change the settings of the TTY control mask, use the command:
expr<ESC>1M
where expr evaluates to the required bit pattern.
You can also open the location addressed by <ESC>1M with one of the
DDT display commands, and deposit an expression that contains the new
bit settings.
Figure 4-1 is an illustration of the effects of bit 17 in the TTY
control mask. The code being examined is the first few lines of
X.MAC, listed in Figure 2-1. The example is not a complete debugging
session; only enough is shown to illustrate the effects of bit 17 of
the TTY control mask. The numbers at the left of the DDT display
lines are to assist you in following the commentary that follows the
display. User input is in lowercase.
|
|
| Figure 4-1: DDT Session Showing Columnar Output
|
|
SCREEN DISPLAY
1. DDT
2. start/ MOVE P,PWORD x$: .$b $g
3. $1B>>START/ MOVE P,PWORD $x
4. P/ -10,,STACK PWORD/ -10,,STACK
5. START+1/ MOVEI IDX,TABLE1 $x
6. IDX/ TABLE1 TABLE1 $1m/ 2 1,,2
7. start$g
8. $1B>>START/ MOVE P,PWORD $x
9. P/ -10,,STACK PWORD/ -10,,STACK
10. START+1/ MOVEI IDX,TABLE1 $x
11. IDX/ TABLE1 TABLE1
COMMENTARY
Line 1:
o DDT is loaded and waiting for a command.
Line 2:
o Enter start/ to examine location start.
o Enter x<ESC>: to open the symbol table for module X.
o Enter .<ESC>b to set breakpoint at location START.
o Enter <ESC>g to begin execution.
4-25
DISPLAYING AND MODIFYING MEMORY
Line 3:
o DDT displays breakpoint information.
o Enter <ESC>x to execute the next instruction.
Line 4:
o DDT displays results of executing the instruction.
Line 5:
o DDT displays the next instruction.
o Enter <ESC>x to execute the instruction.
Line 6:
o DDT displays the results of executing the instruction.
o Enter <ESC>1m/ to display and open the TTY control mask.
o DDT displays the mask. Bit 34 is set.
o Enter 1,,2<RET> to set bits 17 and 34.
Line 7:
o Enter start<ESC>g to restart the program.
Line 8:
o DDT displays the breakpoint information.
o Enter <ESC>x to execute the instruction.
Line 9:
o DDT displays the results of executing the instruction.
Line 10:
o DDT displays the next instruction.
o Enter <ESC>x to execute the next instruction.
Line 11:
o DDT displays the results of executing the instruction.
4-26
CHAPTER 5
CONTROLLING PROGRAM EXECUTION
5.1 BEGINNING EXECUTION
To begin execution of your program, enter:
<ESC>G
Your program will run, beginning at its start address. If you have
not set any breakpoints, your program runs to completion, or until it
makes a fatal error. At TOPS-20 command level, you can then use the
DDT command to reenter DDT and examine your program.
You can start or continue program execution at any address with the
command:
addr<ESC>G
5.2 USING BREAKPOINTS
A breakpoint is a program location that has been altered such that if
your program PC reaches the address of the breakpoint, your program
transfers control to DDT.
When you set a breakpoint with DDT, DDT stores the address of the
breakpoint in an internal table. When you command DDT to begin or
continue program execution, DDT stores the instructions from all
breakpoints in the table, and replaces them with JSRs into a DDT entry
table.
While program execution is suspended at a breakpoint, you can examine
and modify memory, remove breakpoints, insert new breakpoints, execute
individual instructions, and continue program execution.
5-1
CONTROLLING PROGRAM EXECUTION
During this time, the command "<ESC>." returns the value that is the
address of the next instruction to be executed. The command
"<ESC><ESC>." returns a value that is the previous value returned by
"<ESC>.". When you first receive control at the breakpoint, "<ESC>."
returns the address of the breakpoint and "<ESC><ESC>." returns zero.
Before you start execution with <ESC>G, "<ESC>." and "<ESC><ESC>." are
illegal commands (if you try to execute them, DDT sounds the terminal
buzzer or bell and displays a question mark).
NOTE
This manual uses the term "$." to represent the value
returned by the command "<ESC>.", and the term "$$."
to represent the value returned by the command
"<ESC><ESC>.".
You can set up to 12 breakpoints at a time (this is a DDT assembly
parameter) in your program. These breakpoints are numbered 1 through
12. There is also one breakpoint (the unsolicited breakpoint,
numbered zero) that can be used by your MACRO program to "call" DDT.
Each breakpoint has several internal DDT locations associated with it,
which contain information to control DDT action with respect to the
breakpoint. You can examine and modify these DDT locations with the
same DDT commands that you use to examine and modify locations in your
user program. <ESC>nB is a command that returns the value that is the
address of the first DDT word associated with breakpoint n. The
symbol $nB is used here to represent that address.
Table 5-1 contains a list of the breakpoint locations of interest to
the user, and their contents.
Table 5-1: Breakpoint Locations of Interest
LOCATION CONTENTS
$nB Address of breakpoint n.
$nB+1 Instruction for conditional breakpoint n.
$nB+2 Proceed count for conditional breakpoint n.
$nB+3 Address of a location to be opened and displayed when
the breakpoint is reached.
| $nB+4 Address of an ASCIZ DDT command string to be executed
| when the breakpoint is reached.
5-2
CONTROLLING PROGRAM EXECUTION
When your user-program PC reaches a breakpoint, your program executes
the JSR into DDT. When this occurs, DDT does the following:
o saves your user-program context
o replaces the JSR instructions at all breakpoints with the
original program instructions
o displays the breakpoint number, breakpoint address, and the
contents of the breakpoint (depending on bit 16 of the TTY
control mask)
o sets "$." to the breakpoint address
o sets "$$." to zero
o enters the address of the current location (set before you
started the program or proceeded from a breakpoint) on the
location sequence stack
o changes the current location to the breakpoint
o waits for you to give a DDT command
When you command DDT to restart or continue program execution, DDT
does the following:
o saves the program instructions from all breakpoints
o replaces the program instructions at all breakpoints with JSR
instructions to DDT
o if you have not executed the instruction at the breakpoint
with <ESC>X, DDT simulates execution of the instruction at
the breakpoint
o restores your user-program context
o DDT performs a JRSTF (if in section zero, otherwise XJRSTF)
to the next instruction to be executed
5.2.1 Setting Breakpoints
To set a breakpoint, enter:
addr<ESC>{n}B
where addr is the address where you want to suspend execution (addr
can be ".", the command that returns the address of the current
location), and n is the number of the breakpoint (and defaults to the
lowest unused breakpoint number).
5-3
CONTROLLING PROGRAM EXECUTION
If you do not specify n, it defaults to the lowest available (unset)
breakpoint. If you have already set twelve breakpoints, DDT displays
"?" and sounds the terminal buzzer or bell.
If you specify n, it must be greater than zero and less than 13. DDT
restores the original contents of any (previously set) breakpoint
designated as breakpoint n before setting new breakpoint n.
You cannot set more than one breakpoint at the same address. DDT
simply sets the same breakpoint again, even if you explicitly specify
a breakpoint number the second time.
You cannot set a breakpoint at AC zero.
Assume the following conditions:
o location LABL1+3 contains the instruction MOVE 1,LABL2
o breakpoint 2 is set at LABL1+3
If your program reaches LABL1+3 it executes the JSR to DDT, and DDT
does the following:
o saves your user-program context
o restores the original program instructions to the breakpoints
o sets "$." to LABL1+3
o sets "$$." to zero
o enters the address of the current location on the location
sequence stack
o changes the current location to LABL1+3 (the breakpoint)
o opens location LABL1+3
o displays: $2B>>LABL1+3/ MOVE 1,LABL2
To set a breakpoint and have DDT display an additional location when
your program reaches the breakpoint, enter:
addr1<addr2<ESC>{n}B
where addr1 is the location to be displayed, and addr2 is the location
of the breakpoint. Follow addr1 with a left angle bracket (<).
5-4
CONTROLLING PROGRAM EXECUTION
Assume the following conditions:
o location LABL1+3 contains the instruction MOVE 1,LABL2
o location LABL3 contains value SYMBL1
o breakpoint 2 was set by the command:
LABL3<LABL1+3<ESC>B
If your program reaches LABL1+3 it executes the JSR to DDT, and DDT
does the following:
o saves your user-program context
o restores the original program instructions to the breakpoints
o sets "$." to LABL1+3
o sets "$$." to zero
o enters the address of the current location on the location
sequence stack
o changes the current location to LABL1+3 (the breakpoint)
o enters the address of the current location (the breakpoint)
on the location sequence stack
o changes the current location to LABL3
o opens location LABL3
o displays: $2B>>LABL1+3/ MOVE 1,LABL2 LABL3/ SYMBL1
Note that, because DDT placed the breakpoint address on the location
sequence stack, you can enter <ESC><RET> to change the current
location back to the breakpoint.
5-5
CONTROLLING PROGRAM EXECUTION
To display the address of any breakpoint, enter:
<ESC>nB/
where n is the address of the breakpoint. DDT displays the address of
breakpoint n, and you can use the examine commands to open and display
the instruction at breakpoint n. If breakpoint n is not set, DDT
displays zero.
To remove breakpoint n, enter:
0<ESC>nB
To remove all breakpoints, enter:
<ESC>B
5.2.2 Proceeding from Breakpoints
After your program has reached a breakpoint, you can continue
execution at "$." by entering:
<ESC>P
DDT saves the program instructions from all breakpoints, replaces the
program instructions with JSRs to DDT, restores your user-program
context, and if you have not executed any program instructions with
the <ESC>X command, simulates execution of the instruction at the
breakpoint. DDT then executes a JRSTF (in section zero, otherwise DDT
executes an XJRSTF) to the next instruction to be executed.
You can cause the program to start execution at a different location
with the {addr}<ESC>G command, where addr defaults to the program's
start address.
5-6
CONTROLLING PROGRAM EXECUTION
Once your program has reached a breakpoint and DDT has interrupted
execution, you can cause DDT to continue execution but NOT stop at
that breakpoint until your program has reached that breakpoint a
specified number of times. To do this, enter:
expr<ESC>P
where expr is the proceed count. DDT places expr at location $nB+2,
where n is the number of the breakpoint at which your program has
stopped. DDT resumes execution of your program. Each time your
program reaches breakpoint n, DDT decrements the proceed count stored
at $nB+2. Your program continues execution until:
o it reaches a different breakpoint
o it terminates normally
o it commits a fatal error
o the proceed count reaches zero
Each breakpoint has an associated automatic proceed flag. If this
flag is set and the program reaches the breakpoint, DDT decrements the
proceed count at $nB+2 (where n is the number of the breakpoint) and
displays the breakpoint information if the proceed count is less than
one. DDT then automatically continues program execution.
The <ESC>P command resets (clears) the automatic proceed flag
associated with the breakpoint at which DDT has suspended program
execution.
To set a breakpoint and set the associated automatic proceed flag,
enter:
{addr1<}addr2<ESC><ESC>{n}B
where addr2 is the address of the breakpoint and may be ".", addr1 is
an (optional) additional location to be displayed, and n is optional
and defaults to the lowest unused breakpoint.
Each time your program reaches breakpoint n, DDT decrements the
associated proceed count, and if the result is less than one,
displays:
$nB>>addr2/ instr
where n is the breakpoint number, addr2 is the address of the
breakpoint, and instr is the contents of the word at addr2.
5-7
CONTROLLING PROGRAM EXECUTION
If you entered addr1< when you gave the command, DDT displays:
$nB>>addr2/ instr addr1/ contents
where n is the breakpoint number, addr2 is the address of the
breakpoint, instr is the contents of the word at addr2, addr1 is the
additional location to be displayed, and contents is the contents of
the word at addr1.
DDT then automatically continues program execution until:
o your program reaches a different breakpoint
o your program terminates normally
o your program commits a fatal error
o you enter any character while your program is at breakpoint n
You can interrupt the automatic proceed function if you enter a
character while your program is at breakpoint n. DDT then resets the
automatic proceed flag and suspends program execution at the
breakpoint. DDT echoes the character that you entered, which is
otherwise ignored.
To proceed from a breakpoint and set the associated automatic proceed
flag, give the command:
{expr}<ESC><ESC>P
where expr is the proceed count. DDT stores the proceed count at
$nB+2.
5-8
CONTROLLING PROGRAM EXECUTION
5.2.3 Conditional Breakpoints
To cause DDT to interrupt program execution at a breakpoint only if a
specific condition is satisfied, you must store a single test
instruction or a call to a test routine in DDT's breakpoint table.
You can use a test routine in your program, or one that you enter in
DDT's patching area. See Chapter 8 (Inserting Patches with DDT) for
more information about the patching area. To enter the test
instruction (or the call to the test routine), open the DDT location
addressed by the command <ESC>nB+1 by entering:
<ESC>nB+1/
where n is the number of the breakpoint. You must enter n, or DDT
interprets the command as <ESC>B, and removes all breakpoints.
| Deposit the test instruction or the call to the test subroutine. If
| your program reaches breakpoint n, DDT executes the instruction at
$nB+1. DDT then proceeds as follows:
o If the instruction does not cause a program counter skip, DDT
decrements the proceed count at $nB+2. If the result is zero
or less, DDT interrupts execution at breakpoint n.
o If a program counter skip of 1 does occur, DDT interrupts
execution at breakpoint n.
o If the conditional instruction is a call to a subroutine that
returns by skipping over two or more instructions, DDT does
not interrupt program execution.
If DDT interrupts execution because the test instruction resulted in a
program counter skip, DDT displays only one angle bracket after the
breakpoint identification, as:
$3B>LABL1/ MOVE 1,LABL2
5-9
CONTROLLING PROGRAM EXECUTION
5.2.4 The "Unsolicited" Breakpoint
You can cause your MACRO program to "call" DDT by inserting the
following instruction in your program:
JSR $0BPT##
The two pound-signs (##) appended to $0BPT in your MACRO program
declare the symbol as EXTERNAL.
NOTE
"$" represents the dollar sign character, which is
part of the symbol, and is not the DDT echo of the
ESCAPE key.
You must load RDDT.REL with your program or you will get a LINK error
(?LNKUGS undefined global symbol) when you load your program. Load
RDDT.REL with your program as follows (your input is in lowercase; the
last line indicates that DDT is loaded and ready to accept your
commands):
| @link
| */debug filnam/go
| DDT
|
| where filnam is the name of your MACRO-20 program. You can start your
| program running with the <ESC>G command. If your program executes the
| JSR instruction, DDT interrupts program execution and displays:
$0B>>addr+1/ instr
where addr+1 is the first location after the JSR $0BPT instruction,
and instr is the contents of that location.
5-10
CONTROLLING PROGRAM EXECUTION
5.3 EXECUTING EXPLICIT INSTRUCTIONS
To execute a specific instruction, enter the instruction followed by
<ESC>X:
instr<ESC>X
For example:
MOVE 1,@LABL1(3)<ESC>X
After executing the instruction, DDT starts a new line and displays:
o <> if in-line execution of instr would result in
skipping no instructions.
o <SKIP> if in-line execution of instr would result in
skipping 1 instruction.
o <SKIP 2> if in-line execution of instr would result in
skipping 2 instructions.
o <SKIP 3> if in-line execution of instr would result in
skipping 3 instructions.
NOTE
"In-line execution" means execution of the instruction
as part of normal program flow. The execution of
instructions with this command has no effect on your
user-program PC.
This command restores the prevailing display mode.
5.4 SINGLE-STEPPING INSTRUCTIONS
After your program has transferred control to DDT from a breakpoint,
you can execute program instructions one at a time. This is called
"single-stepping."
"<ESC>." is a command that returns the address of the next instruction
to be executed.
To execute the instruction whose address is returned by "<ESC>.",
enter:
<ESC>X
5-11
CONTROLLING PROGRAM EXECUTION
For example, breakpoint 3 is set at LABL1+3. If your program PC
reaches LABL1+3, control passes to DDT, which displays:
$3B>>LABL1+3/ ADD 1,LABL2(2)
Examining the environment, you learn the following:
o AC 1 contains 1
o AC 2 contains 3
o LABL1+4 contains MOVEM 1,@LABL2(3)
o LABL2+3 contains SYM3
as shown by the following terminal display (DDT does not display <LF>
or <ESC>):
$3B>>LABL1+3/ ADD 1,LABL2(2) <ESC>\ SYM3 <LF>
LABL1+4/ MOVEM 1,@LABL2(3) 1/ 1 <LF>
2/ 3
If you now enter the command <ESC>X, DDT does the following:
o changes "$$." to LABL1+3
o executes the instruction at LABL1+3
o changes "$." to LABL1+4
o changes the current location to LABL1+4
o opens LABL1+4
o displays:
1/ SYM3+1 LABL2+3/ SYM3
LABL1+4/ MOVEM 1,@LABL2(3)
If single-stepping an instruction results in a value of ($. minus $$.)
not equal to 1, DDT also begins a new line and displays:
o <SKIP> if ($. minus $$.) = 2
o <SKIP 2> if ($. minus $$.) = 3
o <SKIP 3> if ($. minus $$.) = 4
o <JUMP> if ($. minus $$.) is greater than 4 or less than 1
5-12
CONTROLLING PROGRAM EXECUTION
before displaying the address and contents of the next instruction to
be executed. For example, the following shows a typical terminal
display where you enter <ESC>X to single-step the first instruction at
a breakpoint (DDT echoes <ESC> as $):
$4B>>LABL1+5/ AOSN 3 / 0 <ESC>x
3/ 1
<SKIP>
LABL1+7/ MOVEM 1,LABL2
o
5.5 EXECUTING SUBROUTINES AND RANGES OF INSTRUCTIONS
To execute a series of n instructions beginning with the instruction
whose address is returned by the command "<ESC>.", enter:
n<ESC>X
where n is the number of instructions to execute.
DDT then does the following for each instruction:
o starts a new display line
o executes the instruction
o displays the address of any register or memory location
referenced by the execution of the instruction, and the
contents of those locations after execution of the
instruction
o changes the current location to the next instruction to be
executed
o opens the current location
o displays the address and contents of the next instruction to
be executed
o changes "$." to the address of the next instruction to be
executed
o changes "$$." to the address of the instruction just executed
5-13
CONTROLLING PROGRAM EXECUTION
To suppress typeout of all but the last instruction executed, use the
command:
n<ESC><ESC>X
where n is the number of instructions to execute.
To continue program execution until the PC (program counter) enters a
range of instructions, enter:
{addr1<}{addr2>}<ESC><ESC>X
where addr1 is the lower end of the range, and addr2 is the upper end.
Addr1 defaults to 1 + "$." and addr2 defaults to addr1 + 3. Follow
addr1 with a left angle bracket (<) and addr2 with a right angle
bracket (>).
This command also indicates skips and jumps.
This command is useful for executing a loop or a subroutine call
quickly and without typeout.
For example, breakpoint 3 is at location LABL1.
$3B>>LABL1/ PUSHJ 17,SUBRTN <ESC><ESC>X ;Enter <ESC><ESC>X
<SKIP> ;SUBRTN returns + 2
LABL1+2/ ADD 1,2
If you enter a question mark (?) while DDT is executing an <ESC><ESC>X
command, DDT displays:
Executing: addr/ instr
where addr is the address of the next instruction to be executed, and
instr is the instruction.
To terminate the execution of the series of instructions, enter any
character other than ? (question mark). DDT does the following:
o echoes the character
o displays <SKIP>, <SKIP 2>, <SKIP 3>, or <JUMP>, as
appropriate
o starts a new display line
o changes the current location to the address of the next
instruction to be executed
o displays the address and contents of the current location
5-14
CONTROLLING PROGRAM EXECUTION
o opens the current location
o waits for your next command
5.5.1 Single-Stepping "Dangerous" Instructions
DDT classifies the following as "dangerous" instructions:
o instructions that can modify memory
o instructions that can cause an arithmetic trap
o instructions that can cause a stack overflow
o a monitor call or I/O instruction
Before single-stepping one of these instructions, DDT saves and
replaces the original instructions at the breakpoints with JSRs to
DDT, and restores the full user-program context (including interrupt
system and terminal characteristics) before executing the instruction.
After executing the instruction, DDT replaces the JSRs at the
breakpoints with the original program instructions, and saves the full
user-program context.
DDT does not check whether the instruction actually results in one of
these conditions, only whether the opcode is in the class of
instructions that can cause these effects. This can make executing
subroutines and ranges of instructions under DDT control extremely
time-consuming.
| To execute a subroutine or series of instructions without checking for
| dangerous instructions, use the command:
{addr1<}{addr2>}<ESC><ESC>1X
where addr1 is the lower end of the range, and addr2 is the upper end.
Addr1 defaults to 1 + "$." and addr2 defaults to 3 + addr1. Follow
addr1 with a left angle bracket (<), and addr2 with a right angle
bracket (>).
CAUTION
This command executes much faster than <ESC><ESC>X,
but if the execution of an instruction causes a
software interrupt, the error and trap handling
mechanism may not function correctly. In addition,
program instructions that change or rely on terminal
or job characteristics that are also used by DDT can
cause unpredictable results.
5-15
CONTROLLING PROGRAM EXECUTION
5.6 USER-PROGRAM CONTEXT
When DDT interrupts your program's execution at a breakpoint, and
after it has executed a dangerous instruction during an <ESC>X or
<ESC><ESC>X command, it saves the user-program context. The command
<ESC>nI, where 0<=n<=8 (decimal), returns the address of the word that
contains the information for "function" n. You can use this address
to display and modify these values. Most of these values are useful
only in executive mode. DDT displays the address of the word
containing the information for function n as:
$I+n
where 1<=n<=10 (octal). If n = 0, DDT displays only $I.
| Table 5-2 lists the functions.
Table 5-2: User-Program Context Values
FUNCTION VALUE
0 Executive mode CONI PI.
1 Executive mode PI channels turned off.
2 Executive mode CONI APR.
3 User PC flags.
4 User PC address.
5 EPT page address.
6 UPT page address.
7 CST base virtual address.
10 SPT base virtual address.
DDT restores the user-program context whenever you execute <ESC>G,
<ESC>P, and when you execute <ESC>X, or <ESC><ESC>X of dangerous
instructions.
5-16
CONTROLLING PROGRAM EXECUTION
Functions 5 through 10 (octal) affect DDT's interpretation of your
program's virtual address space. You can alter DDT's interpretation
of your program's virtual address space with the physical and virtual
addressing (<ESC>nU) commands described in Chapter 11 (Physical and
Virtual Addressing Commands). However, any alterations that you make
do not become part of your user-program context, and do not affect
TOPS-20's interpretation of your program's virtual address space.
DDT also saves and restores the user-program ACs as part of the
user-program context. DDT stores the contents of the ACs in an
internal "register" block. Any references you make to addresses 0-17
refer to the relative locations in DDT's internal register block.
These actions are totally transparent to you.
5-17
5-18
CHAPTER 6
SEARCHING FOR DATA PATTERNS IN DDT
With DDT you can search for memory locations that contain a specific
value, and conversely, for words that do not contain a specific value.
You can also set a mask to indicate to DDT that only specified bits
are to be considered when performing the search. In addition, you can
search for words that reference a specific address. You can specify a
range within which to perform the search, or default the range to all
of your program's address space. In either case, DDT compares the
contents of each location within the range with the specified value.
To search for words that match a specific value, enter:
{addr1<}{addr2>}expr<ESC>W
where expr is the value for which DDT is to search, and addr1 and
addr2 delimit the range in which the search is to be conducted.
Follow addr1 with a left angle bracket (<) and addr2 with a right
angle bracket (>). Addr1 defaults to zero and addr2 defaults to
777777 in the current section. Expr can be any legal DDT expression.
DDT does the following:
o compares each location (after ANDing it with the search mask)
within the search range with the 36-bit value resulting from
evaluating expr
o starts the search by comparing the contents of addr1 with
expr
o stops the search after comparing the contents of addr2 with
expr
o displays (on a new line) the address and contents of each
location that matches expr
o enters the address of each matching location on the location
sequence stack
6-1
SEARCHING FOR DATA PATTERNS IN DDT
o sets the current location to addr2
o displays a blank line to indicate the search is over
o restores the prevailing display mode
NOTE
If DDT finds more matching locations than there are
words on the location sequence stack, the earlier
entries are overwritten.
o
To search for words that do NOT match a specified value, enter:
{addr1<}{addr2>}expr<ESC>N
where expr is the value which is not to be matched, and addr1 and
addr2 delimit the range within which DDT is to search. Follow addr1
with a left angle bracket (<) and addr2 with a right angle bracket
(>). Addr1 defaults to zero and addr2 defaults to 777777 in the
current section. Expr is any legal DDT expression.
NOTE
When you use the DDT search functions while running
FILDDT, addr2 defaults to 777777 (in the current
section) unless:
|
| o the target is the running monitor job and you are
| using physical addressing
o the target is an .EXE file and you are using
normal virtual addressing
o the target is a disk structure or data file
In these cases, addr2 defaults to the last word of the
target. See Chapter 9 (FILDDT), and Chapter 11
(Physical and Virtual Addressing Commands), for more
information.
6-2
SEARCHING FOR DATA PATTERNS IN DDT
DDT functions as for the <ESC>W command, except:
o DDT searches for and displays the address and contents of any
word within the address range that does NOT match the 36-bit
value resulting from evaluating expr.
o DDT enters the locations of non-matching words on the
location sequence stack.
o
To search for references to an address, enter:
{addr1<}{addr2>}expr<ESC>E
where addr1 and addr2 delimit the range of the search, and expr
contains the address for which DDT is to search. Follow addr1 with a
left angle bracket (<) and addr2 with a right angle bracket (>).
Addr1 defaults to zero and addr2 defaults to 777777 in the current
section. Expr is any legal DDT expression. DDT performs an IFIW
effective address calculation on the expression contained in each word
within the range, and uses the 18-bit result to determine whether
there is a match.
Thus, if bits 14-17 (the X field of an instruction) or bit 13 (the I
field of an instruction) are nonzero, indexing or indirection may
result in DDT finding different search results at different times.
DDT does not check whether the expression is actually an instruction
before performing the effective address calculation.
o
If you enter a question mark (?) while DDT is performing any of the
above searches, DDT displays:
Searching: addr/ value
where addr is the address of the location that will next compare, and
value is the contents of addr.
To abort the search, enter any character other than question mark (?).
DDT stops searching, and waits for more input. The character that you
enter to terminate the search is otherwise ignored.
| Each of the above search commands restores the prevailing display
| mode.
6-3
SEARCHING FOR DATA PATTERNS IN DDT
<ESC>M is a command that addresses a DDT location that contains a
search mask used to prevent specified bits in the memory word from
being considered during the search. This mask is used only by <ESC>W
and <ESC>N, not by <ESC>E. DDT logically ANDs the search mask with
the memory word before making the comparison, but does not change the
memory word. If DDT finds a match, it displays the entire word.
DDT sets the search mask to 777777,,777777 (compare all 36 bits) by
default.
To set the search mask, enter:
expr<ESC>M
where expr evaluates to the required bit pattern.
For example, to search for all of the RADIX50 references to MAIN.
(user input is in lowercase):
<ESC><ESC>5t ;Set typeout mode to RADIX50.
37777,,777777<ESC>m ;Ignore the left 4 bits.
main.<ESC>5"<ESC>w ;Enter RADIX50 symbol, start search.
4112/ 4 MAIN. ;DDT displays match found.
4775/ 0 MAIN. ;DDT displays match found.
;Search over, DDT displays blank line.
You can also examine and modify the search mask with the examine and
deposit commands described in Chapter 4 (Displaying and Modifying
Memory).
6-4
CHAPTER 7
MANIPULATING SYMBOLS IN DDT
7.1 OPENING AND CLOSING SYMBOL TABLES
Each separate program module has its own symbol table. When
displaying a value symbolically, if more than one symbol is defined
with that value, DDT displays the first global symbol found. When
searching for a symbol, DDT searches the "open" symbol table first.
For display purposes, DDT treats local symbols found in the open
symbol table as global symbols. DDT appends a pound-sign (#) to local
symbol names that it finds in a symbol table that is not open. For
example:
SYMBL1#
where SYMBL1 is a local symbol that DDT found in a symbol table that
is not open.
If you enter an expression that contains a symbol that is defined in
more than one of your program modules, DDT uses the value of the
symbol that is contained in the open symbol table. If the symbol is
not defined in the open symbol table, or if there is no open module
and there is not a global definition of the symbol, DDT displays:
M
To open the symbol table of a program module, enter:
name<ESC>:
where name is the name of the program module as specified by the TITLE
pseudo-op in your MACRO-10 program (or the equivalent mechanism in a
higher-level language program). DDT closes any currently open symbol
table and opens the symbol table associated with module name.
7-1
MANIPULATING SYMBOLS IN DDT
To find the name of the module associated with the open symbol table,
enter:
<ESC>1:
If there is an open symbol table, DDT displays the name of the module
associated with the open symbol table. For example, if the symbol
table for module X is open, the screen display is as follows (DDT
echoes <ESC> as $, and does not display any spaces between the command
and the module name):
$1:/X
If there is no open symbol table, DDT displays three spaces (or a tab,
depending on the TTY control mask), and waits for your next command.
To close the open symbol table, enter:
<ESC>:
7.2 DEFINING SYMBOLS
To redefine a symbol or to create a new symbol in the current symbol
table, enter:
expr<symbol:
where expr is any legal DDT expression, and symbol is the symbol name.
To define symbol as the address of the open location, enter the
command:
symbol:
| If there is no open location, DDT uses the address of the last
| location that was open. DDT defines symbol as a global symbol. If
| you previously used symbol as an undefined symbol, DDT inserts the
| correct value in all the places you referenced symbol, and removes
| symbol from the undefined symbol table.
7-2
MANIPULATING SYMBOLS IN DDT
7.3 SUPPRESSING SYMBOL TYPEOUT
To prevent a symbol from being displayed, enter:
symbol<ESC>K
where symbol is the symbol to be suppressed. DDT still accepts symbol
as input, but no longer displays symbol as output.
To suppress the last symbol that DDT displayed (in an address, in the
contents of a memory word, or in the evaluation of an expression),
enter:
<ESC>D
DDT suppresses the last symbol displayed, and then redisplays the
current quantity. DDT does not display its usual three spaces between
the command and the displayed value.
In the following example, assume that symbol SIZE is defined as 3.
User typein is lowercase (<LF> does not appear on the terminal
screen).
start/ JFCL 0 <LF>
LOOP/ AOS 1 <LF>
LOOP+1/ MOVE 2,1 <ESC>dMOVE 2,1 <LF>
START+3/ MULI 2,SIZE <ESC>dMULI 2,3
To reactivate a symbol for typeout, redefine the symbol. For example,
to reactivate the display of symbol SIZE, above, enter:
size<size:
Note that SIZE is now defined as a global symbol, even if it was
previously a local symbol.
7.4 KILLING SYMBOLS
To remove a symbol from the symbol table, enter:
symbol<ESC><ESC>K
DDT removes symbol from the symbol table, and no longer displays
symbol or accepts symbol as input.
7-3
MANIPULATING SYMBOLS IN DDT
7.5 CREATING UNDEFINED SYMBOLS
It is sometimes convenient to use symbols that have not yet been
defined. To create an undefined symbol, enter:
symbol#
where symbol is the undefined symbol name. DDT enters symbol in the
undefined symbol table. When you later define the symbol, DDT enters
it into the defined symbol table, removes it from the undefined symbol
table, and enters the correct value in all locations where you
referenced the symbol.
You can use undefined symbols only as parts of expressions that you
are depositing to memory. Undefined symbols can be either fullword or
right-halfword values; they cannot be used as the A or X fields of an
instruction, or as the left-halfword of an expression.
|
|
|
| 7.6 FINDING WHERE A SYMBOL IS DEFINED
|
To determine the modules in which a symbol is defined, enter:
symbol?
where symbol is the name of the symbol. DDT displays the name of each
program module in which symbol is defined. If the symbol is a global
symbol, DDT displays a "G", as:
sym?
MAIN. G
DDT does not display G following a local symbol found in the open
symbol table. When DDT has searched the entire symbol table, it
displays a blank line.
7-4
MANIPULATING SYMBOLS IN DDT
7.7 SEARCHING FOR SYMBOLS
To search for all the symbols that begin with a specific character
pattern, use the command
sym<ESC>?
where sym is the character pattern for which you are searching, and
may be one to six characters long. DDT searches your symbol tables
and displays all symbols that begin with that pattern. DDT also
displays all modules in which the symbol is found, whether the symbol
is global, and the value of the symbol. In addition, if the symbol
represents a value in which only one bit is set, DDT displays the
number of the bit. For example, the command
fdb<ESC>?
might cause the following display:
FDBIN INOUT G 3
FDBOUT INOUT G 2 (1B34)
FDB MOD1 7
7.8 LISTING UNDEFINED SYMBOLS
To get a list of all currently undefined symbols, enter:
?
DDT displays a list containing each undefined symbol.
|
|
|
| 7.9 LISTING SYMBOLS
|
| To get a list of all symbols starting with a certain character or set
| of characters, enter:
|
| {val1<{val2>}}{sym}<ESC>{n}?
|
| where val1 and val2 restrict the values of symbols which DDT displays.
| If only val1 is present, only symbols having that value are displayed.
| If both val1 and val2 are present, symbols with (signed) values
| between val1 and val2 inclusive are displayed. The n argument is an
| octal mask of flags.
|
| If bit 35 is on, only symbols defined in the open module are
| displayed. If any of bits 33-30 are on, the corresponding bit from
| 0-3 must be present in the symbol's definition. Any other bits are in
| error.
7-5
MANIPULATING SYMBOLS IN DDT
| For example, entering "<ESC>4?" displays all global symbols, "<ESC>1?"
| displays all symbols defined in the open module, and "5<100>T<ESC>5?"
| displays all global symbols defined in the open module, starting with
| "T", whose values are in the range of 5-100.
7.10 LOCATING SYMBOL TABLES WITH PROGRAM DATA VECTORS
DDT Version 44 can access symbol tables pointed to by JOBDAT, by PDVs
(program data vectors) and by values you store in DDT.
The command <ESC>5M returns the address of a DDT location that
contains information to direct DDT to the current symbol table. The
symbol $5M refers to the memory location at the address returned by
the <ESC>5M command.
If the value contained in $5M is negative (bit 0 is set), the
right-halfword contains the number of the section that contains the
JOBDAT area.
If the value contained in $5M is positive (bit zero is clear, and the
value in $5M is nonzero), $5M contains the 30-bit address of the PDV
currently in use by DDT.
If $5M contains zero, DDT uses values (which can be stored by the
user) pointed to by locations 770001 and 770002 of UDDT, to determine
which symbol table(s) to use. The algorithm that DDT uses is
described below.
To set $5M to a PDV address, type in
addr<ESC>5M
where addr is the the PDV address. If you know the PDV name, you can
type in
<ESC><ESC>:/name/
where name is the name of the PDV, and the slashes (/) represent any
characters that do not appear in name. If name is a null string, DDT
searches for a PDV with no name or a null name. DDT ignores any
characters in name beyond a length of 39.
DDT searches for a PDV named name, and places its address in $5M. If
DDT does not find the PDV, it displays ? and sounds the terminal
buzzer or bell.
7-6
MANIPULATING SYMBOLS IN DDT
You can learn the names of the PDVs associated with your program by
using the following sequence of TOPS-20 commands:
@GET program-name
@INFORMATION VERSION
To display the name of the PDV addressed by $5M, type in
<ESC><ESC>1:
If $5M contains the address of a PDV, DDT displays the name of the
PDV; otherwise, it does nothing.
Whenever DDT is entered from its start address or from a breakpoint,
if $5M is zero, DDT initializes $5M according to the following rules:
o If XDDT was started by the UDDT stub, AND the location
addressed by location 770001 in the stub has bit zero set:
> DDT uses the location addressed by location 770001 (in
the stub) as an IOWD pointer to a symbol table in the
section that contains the stub.
> DDT uses the location addressed by location 770002 (in
the stub) as as IOWD pointer to the undefined symbol
table in the section that contains the stub.
o If XDDT was not started by the UDDT stub, OR the location
addressed by location 770001 in the stub has bit zero clear:
> If no PDVs exist, DDT sets $5M to -1,,n, where n is:
* the section that contains the UDDT stub (if the stub
exists) OR
* the section that contains the entry vector (if an
entry vector exists) OR
* section zero.
> If there is one (only) PDV, DDT sets $5M to the address
of the PDV.
7-7
MANIPULATING SYMBOLS IN DDT
> If there is more than one PDV, DDT examines word .PVSYM
of each PDV in ascending memory order (DDT first looks at
the PDV closest to 0,,0). DDT then sets $5M to:
* the address of the first (lowest in memory) PDV that
contains a .PVSYM word that contains a global address
(if there is one).
* the address of the first (lowest in memory) PDV that
exists in or above the section containing the entry
vector (if there is one).
* the address of the first (lowest in memory) PDV.
NOTE
DDT ignores its own PDV when setting
$5M.
7-8
CHAPTER 8
INSERTING PATCHES WITH DDT
To replace the instruction at the open location with a series of
instructions and test the new instructions without reassembling your
program, you can use the DDT patch function. DDT deposits (in a
patching area) the replaced instruction, the new series of
instructions, and one or more JUMPA instructions back to the main line
of your program. DDT also deposits (in the location that contains the
replaced instruction) a JUMPA instruction to the first word of the
patch.
To insert a patch that will be executed before the instruction at the
open location, enter:
{expr}<ESC><
where expr is the start of the patching location, and defaults first
to PAT.., then to PATCH. KDDT and MDDT default to FFF (an area
created during the monitor build), PAT.., and PATCH, in that order.
If you do not enter expr, and DDT finds none of the default symbols,
DDT uses the value contained in JOBDAT location .JBFF as the address
to begin the patch. If expr is a symbol (or the default), DDT updates
the symbol table when you terminate the patch, so that the symbol
identifies the first word after the patch that you just terminated.
o
If there is no open location when you initiate the patch, DDT displays
"?" and sounds the terminal buzzer or bell.
NOTE
If expr is an AC address, or resolves to a value less
than 0,,140, DDT displays "?" and sounds the terminal
buzzer or bell.
8-1
INSERTING PATCHES WITH DDT
When you issue a command to start a patch, DDT saves the address of
the open location, closes the open location, changes the current
location to the first word in the patching area, and opens that word.
DDT also displays the address and contents of the first word of the
patching area. For example:
<ESC><
PAT../ 0
You can now enter the patch, using deposit instructions (the expr<LF>
format is probably most useful). DDT updates the current and open
locations according to the rules for the command that you use.
To terminate the patch, enter:
{expr}<ESC>{n}>
where expr is the last word of the patch you are entering, and n is
the number of returns possible from execution of the patch. The
default for n is 2, allowing for a return to 1 + the address of the
instruction being replaced, and for a "skip return" to 2 + the address
of the instruction being replaced.
When you terminate the patch, DDT deposits the instruction being
replaced into the first location following the current location,
unless:
o display is not suppressed by ! AND
o the current location is zero AND
o the current location is closed OR you omitted expr
in which case DDT deposits the instruction being replaced into the
current location. This prevents the patch from containing unintended
null words.
DDT deposits n JUMPA instructions in the locations immediately
following the one in which it deposited the original program
instruction. The first JUMPA instruction has 1 in its A field, and
jumps to 1 + the address of the replaced instruction, the second JUMPA
instruction has 2 in its A field and jumps to 2 + the address of the
replaced instruction, and so on. The AC numbers are used for
identification purposes only. Any JUMPA instruction beyond the
sixteenth contains 17 in its A field.
DDT then changes the current location to the location that was open
when you initiated the patch, deposits in the current location a JUMPA
instruction to the first word of the patch that you entered, and
displays the address, original contents, and new contents of the
current location. The current location is "open", and can be modified
by your next command.
8-2
INSERTING PATCHES WITH DDT
If you default expr, or enter a symbol in the {expr}<ESC>< command,
when you terminate the patch, DDT redefines the symbol that identifies
the start of the patch. If DDT used the value contained in JOBDAT
location .JBFF as the address of the patching area, DDT changes the
values contained in .JBFF and the left half of JOBDAT location .JBSA.
In all cases, the new value is the address of the memory location
after the last word of the patch.
By default, there are 100 (octal) words in the patching area. DDT
does not check whether your patch overflows the patching area. You
can control the size of the patching area with the /PATCHSIZE switch
in LINK.
NOTE
DDT allows you to use other DDT commands while you are
in the process of entering a patch. DDT does not
check whether the current and open locations are in
the patching area, or whether you are entering patch
instructions in sequence. When you terminate the
patch, DDT deposits the instruction being replaced in
the current location regardless of whether the current
location is in the patching area.
To insert a patch that will be executed after the instruction at the
open location, enter:
{expr}<ESC><ESC><
where expr is the address of the patching location (PAT.. is the
default). The results are the same as inserting the patch before the
instruction as above, except:
o When you open the patch DDT deposits the replaced instruction
in the first word of the patch.
o When you terminate the patch, DDT deposits the first JUMPA
instruction (rather than the instruction being replaced) in
the first location following the current location unless:
> display is not suppressed by ! AND
> the current location is zero AND
> the current location is closed OR you omitted expr
in which case DDT deposits the first JUMPA instruction in the
current location. This is to prevent the patch from
containing unintended null words.
8-3
INSERTING PATCHES WITH DDT
NOTE
If expr is an AC address, or resolves to a value less
than 0,,140, DDT displays "?" and sounds the terminal
buzzer or bell.
Figure 8-1 illustrates the patching function. The program being
patched is X.MAC (see Figure 2-1). The patch inserts a SKIPN
instruction that is to be executed after the instruction at START+4.
Figure 8-1: Annotated Patching Session
DDT OUTPUT USER INPUT EXPLANATION
START+4/ MOVE 2(IDX) As a result of your last
command, DDT displays the
contents of START+4.
| <ESC><ESC>< Enter <ESC><ESC>< to start
| the patch.
|
| PAT../ 0 MOVE 2(IDX) DDT displays the address
| and contents of the first
| word of the patch area, and
| deposits the instruction from
| START+4 in the first word of
| the patch.
|
| PAT..+1/ 0 DDT displays the address
| and contents of the next word
| of the patch area.
|
| pat..= Check the address of PAT.."
| (the first word of the patch
| area).
14432 DDT displays the current
address of "PAT..".
| skipn 1,0<ESC>2> Enter the new instruction,
| and terminate the patch with
| a normal return and one skip
| return by entering <ESC>2>.
|
| PAT..+2/ 0 JUMPA 1,START+5 DDT displays the next word
| of the patch area, then
| deposits a JUMPA instruction
| to 1 + the address of the
| replaced instruction.
8-4
INSERTING PATCHES WITH DDT
| Figure 8-1: Annotated Patching Session (Cont.)
|
|
| DDT OUTPUT USER INPUT EXPLANATION
|
| PAT..+3/ 0 JUMPA 2,START+6 DDT displays the address
| and contents of the next word
| of the patch area, then
| deposits a JUMPA instruction
| to 2 + the address of the
| replaced instruction.
START+4/ MOVE 2(IDX) JUMPA STACK+10
DDT displays the address
and original contents of the
replaced instruction, then
deposits and displays a
JUMPA instruction to the
first word of the patch.
START+4 is the current
location, and is "open".
pat..= Check the address of the
patch area.
14436 DDT updated "PAT..".
Figure 8-2 shows the terminal display as it actually appears when you
insert the patch described above. Your input is in lowercase.
Figure 8-2: Terminal Display of Patching After an Instruction
| START+4/ MOVE 2(IDX) $$<
| PAT../ 0 MOVE 2(IDX)
| PAT..+1/ 0 pat..=14432 skipn 1,0$2>
| PAT..+2/ 0 JUMPA 1,START+5
| PAT..+3/ 0 JUMPA 2,START+6
| START+4/ MOVE 2(IDX) JUMPA STACK+10 pat..=14436
| Figure 8-3 shows the terminal display when inserting the same patch
| before the instruction at START+4. You enter the instruction in the
| form expr<LF> (user input is lowercase). Note the use of the patch
termination command without expr and without n.
8-5
INSERTING PATCHES WITH DDT
Figure 8-3: Terminal Display of Patching Before an Instruction
| START+4/ MOVE 2(IDX) $<
| PAT../ 0 .=14432 skipn 1,0
| PAT..+1/ 0 $>
| PAT..+1/ 0 MOVE 2(IDX)
| PAT..+2/ 0 JUMPA 1,START+5
| PAT..+3/ 0 JUMPA 2,START+6
| START+4/ MOVE 2(IDX) JUMPA STACK+10 pat..=14436
To abort the patch you are entering, enter:
<ESC>0<
DDT displays 3 spaces (or a tab, depending on the TTY control mask)
and changes the current location to the location that was open when
you initiated the patch. The symbol that denotes the start of the
patching area is unchanged. Any deposits that you made as part of the
patch remain in the patching area. This allows you to restart the
same patch, or to write over the patch with a new one.
8-6
CHAPTER 9
FILDDT
9.1 INTRODUCTION
FILDDT is a utility used to examine and change disk files and physical
disk blocks. You can also use FILDDT to examine monitor crash dumps,
and to examine the running monitor. With FILDDT, you can look at .EXE
files as if they had been loaded with the monitor GET command, or as
if they were binary data files.
In selecting a disk file, a disk, or the monitor with FILDDT, you are
really establishing the virtual address space that FILDDT accesses.
When discussing the contents of that virtual address space, where the
contents can be any of the above objects, this chapter uses the term
target.
Once you have accessed a target, you can examine and modify it with
the DDT examine and modify commands (you cannot modify the running
monitor with FILDDT), and then save it with your modifications. You
can use all of DDT's commands for examining and modifying memory, but
you cannot use any commands that cause the execution of program
instructions, such as <ESC>X, <ESC>G, and so on. If you attempt to
execute a program instruction, FILDDT sounds the terminal buzzer or
bell.
9.2 USING FILDDT
There are two command levels in FILDDT. This document refers to these
two levels as FILDDT command level and DDT command level.
FILDDT command level accepts FILDDT commands to control session
parameters and to select the target. FILDDT command level employs
TOPS-20 command recognition and help. When at FILDDT command level,
FILDDT displays the prompt:
FILDDT>
9-1
FILDDT
Once you access a target, FILDDT enters DDT command level. At DDT
command level, use DDT commands to examine and modify the target.
The syntax of a FILDDT command-level command is:
command {file-spec{/switch...}}
where command is a FILDDT command-level command, file-spec is a
TOPS-20 file specification, and switch invokes a specific function or
parameter about the function that you can perform (enable patching,
for example). You can use FILDDT commands to invoke functions and
parameters that are invoked by analogous FILDDT switches.
With a FILDDT command you can:
o request HELP on FILDDT
o specify the target to be examined
o invoke FILDDT functions
o establish certain parameters about the functions that you can
perform
o enter DDT command level
o exit FILDDT
A FILDDT command can have more than one of the above effects.
The commands and switches are described in detail in the rest of this
chapter.
To start FILDDT, enter the TOPS-20 command:
FILDDT
FILDDT enters FILDDT command level and prompts:
FILDDT>
You can now use the FILDDT commands described on the following pages.
9-2
FILDDT
9.2.1 FILDDT Commands
There are two classes of FILDDT-level commands; those that select the
target that FILDDT is to access and those that establish what function
FILDDT is to perform for the target (enable patching, extract symbols,
and treat an .EXE file as data). The following are the targets
(virtual address spaces) that FILDDT can access, and the commands that
select them:
TARGET COMMANDS
Disk files GET
Disk structures DRIVE, STRUCTURE
The running monitor PEEK
To examine and patch disk structures, you must have WHEEL, OPERATOR,
or MAINTENANCE privileges enabled. To examine the running monitor,
you must have WHEEL or OPERATOR privileges enabled.
Following are the parameters you can invoke for the target and the
commands and switches that select them:
FUNCTION COMMAND SWITCH
Treat file as pure binary data ENABLE DATA-FILE /DATA
Enable patching ENABLE PATCHING /PATCH
Enable thawed access ENABLE THAWED /THAWED
Load symbol table only from file LOAD /SYMBOL
To get HELP, enter:
HELP
FILDDT displays a very brief description of the FILDDT commands and
redisplays the FILDDT> prompt.
To return to TOPS-20 command level from FILDDT command level, enter:
EXIT
9-3
FILDDT
9.2.2 Symbols
To enhance performance, FILDDT uses a symbol table that it builds in
its own address space, rather than one which exists in the target
address space.
FILDDT automatically extracts symbols to build its internal symbol
table from the first .EXE file it loads during a session. Once FILDDT
has an internal symbol table, it ignores any symbols in subsequently
loaded .EXE files unless you use the LOAD command or the GET command
with the SYMBOL switch.
9.2.3 Commands to Establish Formats and Parameters
ENABLE DATA-FILE
If you specify an .EXE file, DDT (by default) loads the file in
virtual memory as if it were to be executed. You can use the
ENABLE DATA-FILE command to look at an .EXE file as if it were a
data file. FILDDT then loads the entire file (including the .EXE
directory block) as a binary file, starting at virtual location
zero. You can accomplish the same thing by appending the /DATA
switch to the file-spec when you use the GET command.
ENABLE PATCHING
The ENABLE PATCHING lets you modify the target. You can also
enable patching by appending the /PATCH switch to the file-spec
when you use the GET command. If you do not enable patching, you
can only examine the target. If you attempt to modify the target
but have not enabled patching, FILDDT displays:
? Patching is not enabled
Note that you cannot enable patching in FILDDT with the <ESC>W
command.
ENABLE THAWED
The ENABLE THAWED command lets you examine and modify (if you
enable patching) files that require thawed access. You can also
use the /THAWED switch when loading the file with the GET
command.
9-4
FILDDT
LOAD
The LOAD command tells FILDDT to copy the symbol table from
the file named by file-spec. Once FILDDT has built its
internal symbol table, FILDDT displays:
[Extracting symbols from file file-spec]
[n symbols loaded from file]
where n is the number of symbols that FILDDT extracted from
the file. FILDDT then again prompts you with FILDDT>.
You can also load symbols from the file you specify in the
GET command by appending the /SYMBOL switch to the
file-spec.
If the file you specify is not an .EXE file, FILDDT
displays:
% Not in .EXE format -- Data file assumed.
[Extracting symbols from file file-spec]
? Symbols cannot be extracted from a data file
FILDDT then redisplays its prompt.
9.2.4 Commands to Access the Target and Enter DDT
DRIVE
The DRIVE command allows you to access a physical structure
directly. This may be useful if the home block has been
damaged. To access disk structures with FILDDT, you must
have WHEEL, OPERATOR, or MAINTENANCE privileges enabled.
If you wish to be able to patch the disk structure, you must
give the ENABLE PATCHING command before using the DRIVE
command.
To access the disk structure, enter:
DRIVE c k u
where c is the channel, k is the controller, and u is the
unit, in decimal.
9-5
FILDDT
If the unit is part of a mounted structure, FILDDT displays:
[Unit is part of structure name]
where name is the logical name of the disk structure.
If FILDDT successfully access the unit, FILDDT enters DDT
command level and displays:
[Looking at unit u on controller k on channel c]
where c is the channel, k is the controller, and u is the
unit, in decimal.
GET
The GET command tells FILDDT to load the file you name,
invoke any parameters for which you specify switches, and
enter DDT command level. Legal switches are /DATA, /PATCH,
/SYMBOL, and /THAWED, and correspond to the ENABLE
DATA-FILE, ENABLE PATCHING, LOAD, and ENABLE THAWED
commands, respectively.
If FILDDT extracts symbols and builds an internal symbol
table, it displays:
[Extracting symbols from file file-spec]
[n symbols loaded from file]
where n is the number of symbols loaded.
When FILDDT has loaded the file, it displays:
[Looking at file file-spec]
where file-spec is the TOPS-20 file specification of the
file.
If FILDDT does not find the file, it displays:
? Invalid file specification, message
where message is a TOPS-20 error string.
9-6
FILDDT
PEEK
Use the PEEK command to examine the running monitor. To use
FILDDT to examine the running monitor, you must have WHEEL
or OPERATOR privileges enabled.
Once you have invoked FILDDT, if you wish to be able to use
monitor symbols when looking at the running monitor, you
must use the LOAD command first, as:
LOAD SYSTEM:MONITR.EXE
You cannot patch the running monitor with FILDDT.
To examine the running monitor, enter:
PEEK
FILDDT displays:
[Looking at running monitor]
and enters DDT command level.
NOTE
You cannot use FILDDT to PEEK
at the running monitor unless
you are using normal virtual
addressing. If you are
PEEKing the monitor and change
memory mapping to a mode other
than normal virtual addressing
with the n<ESC>0U, n<ESC>1U,
n<ESC>2U, or $$U commands,
FILDDT does not give an error.
However, every page in the
monitor then appears to DDT to
be non-existent. In this
case, most attempts to
reference memory causes DDT to
display ?, sound the terminal
buzzer or bell, and set the
error string to "CAN'T PEEK
PHYSICAL". Searches do not
cause errors, but never
discover matches.
9-7
FILDDT
STRUCTURE
The STRUCTURE command allows you to access a disk structure
by its logical name. To access disk structures with FILDDT,
you must have WHEEL, OPERATOR, or MAINTENANCE privileges
enabled.
If you wish to be able to patch the disk structure, you must
give the ENABLE PATCHING command before using the STRUCTURE
command.
To examine a disk structure, enter:
STRUCTURE name
where name is the logical name of the structure. If the
structure contains more than one physical disk, you can
access the entire logical structure.
If FILDDT successfully accesses the structure, it enters DDT
command level and displays:
[Looking at file structure name]
where name is the logical name of the structure.
9.2.5 Exiting FILDDT
When you are through examining and modifying the target, save the
modified file by entering:
<CTRL/E>
FILDDT closes the file, saving any changes that you have made,
and returns to FILDDT command level.
Any symbol table that you have loaded (explicitly or by default)
remains loaded until you specify another with the LOAD command or
the /SYMBOL switch.
If you have modified symbols, FILDDT also modifies the symbol
table of the disk file, if one of the following occurred:
o FILDDT automatically loaded the symbol table.
o you loaded the symbol table and entered DDT command level by
entering:
GET file-spec/SYMBOL
9-8
FILDDT
| FILDDT sometimes runs out of memory when you use the <CTRL/E>
| command to save files without exiting FILDDT. If FILDDT runs out
| of memory while loading a file, it displays the message:
|
| ? Not enough memory for file pages
|
| If FILDDT runs out of space while building a symbol table, it
| displays the message:
|
| ? Not enough memory for symbols
|
| To reclaim all of your available memory, exit FILDDT with the
| <CTRL/Z> command, and then restart FILDDT with the TOPS-20
| command FILDDT. Note that this technique restores standard
| virtual addressing conditions, as if you had used the <ESC>U
| command. See Chapter 11 (Physical and Virtual Addressing
| Commands) for more information about virtual addressing
| conditions.
To close the file, save all modifications (as with <CTRL/E>,
above) and exit from FILDDT, enter:
<CTRL/Z>
| If you exit FILDDT by entering <CTRL/C>, changes that you make to
| a disk file can still be in FILDDT's output buffer; if so, they
| will NOT be saved.
When you exit FILDDT, you can save FILDDT with its internal
symbol table. This saves time if you often use FILDDT to debug a
specific file (such as the monitor) that has a very large symbol
table. Start FILDDT, load the symbol table, then exit. Use the
TOPS-20 SAVE command to create a copy of FILDDT to be used with
that specific file.
For example (your input is in lowercase):
@filddt
FILDDT>load system:monitr.exe
[34472 symbols loaded from file]
FILDDT>exit
@save
FILDDT.EXE.1 Saved
9-9
10-1
CHAPTER 10
PRIVILEGED MODES OF DDT
NOTE
This chapter makes no attempt to explain
internal monitor mechanisms. This
chapter assumes that you are aware of
various monitor contexts. Certain
monitor contexts may interfere with or
be interfered with by DDT context
switching. It is up to you to be aware
of these. Note also that internal
monitor locations that are used in
examples in this chapter are subject to
change in subsequent monitor releases.
10-1
PRIVILEGED MODES OF DDT
10.1 MDDT
MDDT is used to debug and patch the running monitor during
timesharing, and is an integral part of the swappable monitor. To run
MDDT, you must have WHEEL or OPERATOR privileges enabled.
To invoke MDDT, start DDT and then execute the MDDT% JSYS. For
example (user input is lowercase):
@enable
$ddt
DDT
mddt%<ESC>x
MDDT
You can also invoke MDDT by running a MACRO-20 program that executes
the MDDT% JSYS.
MDDT runs in the executive virtual address space of the process that
executed the MDDT% JSYS. While in MDDT, you are still running in user
context, you are running under timesharing, and your process is
subject to being swapped out, as is any other user process.
If for some reason you cannot access system files, you can enter MDDT
through the MEXEC, as follows:
@enable
$<CTRL/E>QUIT
MX>/
where the / (slash) command to MEXEC enters MDDT.
To exit MDDT, enter:
mretn<ESC>g
or enter:
<CTRL/Z>.
10-2
PRIVILEGED MODES OF DDT
10.2 KDDT
You can run KDDT in executive mode or in user mode. KDDT in executive
mode is used to debug parts of the monitor which can not be debugged
interactively such as those modules that deal with physical memory or
paging. KDDT in user mode is used to debug and patch the monitor .EXE
file, which you can then save for BOOTing at a later time.
KDDT is part of the resident monitor. When running KDDT in executive
mode, you can exercise any normal DDT functions, such as changing
memory and setting breakpoints. When you stop at a breakpoint and
control passes to KDDT, timesharing (if in effect) ceases.
To run KDDT in executive mode use the /E command when BOOTing the
monitor. For example (user input is in lowercase):
BOOT>/e ;Type in /e
[BOOT: LOADING] [OK]
EDDT ;EDDT is loaded and waiting for your command
Your debugging may be easier if you lock the swappable monitor in
core. You can do this by executing the instruction that calls monitor
routine SWPMLK. For example:
CALL SWPMLK<ESC>X
To run KDDT in user mode:
@get system:monitr.exe
@start 140
DDT
You can use KDDT in user mode to patch the monitor (.EXE file) which
will be booted the next time the system is BOOTed up.
After you have started KDDT as above, use the DDT patching commands to
insert your patch. When your patch is complete, exit KDDT with
<CTRL/Z> and use the TOPS-20 SAVE command to save the patched version
of the monitor. For example:
<ESC>< ;ESCAPE key followed by a left angle
;bracket.
....
.... ;Type in the patch.
<ESC>> ;ESCAPE key followed by right angle
;bracket.
<CTRL/Z> ;Exit KDDT
@save system:monitr.exe ;Save the new version.
10-3
PRIVILEGED MODES OF DDT
10.3 EDDT
You can use EDDT to debug user programs that run in executive mode.
You must load EDDT.REL with your program, as follows:
@LINK
SYS:EDDT.REL,PROG/GO
@SAVE PROG
where PROG is the name of your MACRO-20 program.
10-4
10-5
11-1
CHAPTER 11
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
| All TOPS-20 DDTs (including FILDDT) can do their own page mapping.
| The commands described in this chapter allow you to set parameters to
govern the interpretation of the address space which you are
examining. You can control the mapping of the address space you are
examining by choosing to use or bypass the user process table (UPT) or
the executive process table (EPT). You can choose which special pages
table (SPT) to use, and which hardware register block to use. Other
commands allow you to emulate either KI-paging or KL-paging, control
address relocation, and set memory protection limits. In each of the
following commands, the argument (page, addr, n) defaults to zero.
NOTE
The DDT commands <ESC>G, <ESC>P, and <ESC>X have side
effects that affect your control over physical and
virtual addressing. In addition to their normal
functions, these commands also do the following:
o restore normal virtual addressing as if <ESC>U had
been given (<ESC>X does NOT do this)
o set the FAKEAC flag (as if <ESC>U had been given)
o clear the relocation factor (as if 0<ESC>8U had
been given)
o reset the address-protection address to infinity
(377777,,777777)
o restore the active hardware register block to the
one in use before any <ESC>4U command was given
11-1
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
COMMAND EXPLANATION
<ESC>U
This command enables memory mapping by standard TOPS-20 virtual
addressing. When you give this command, DDT restores the virtual
addressing conditions that were in effect before any
{<ESC>}<ESC>nU (where 0<=n<=2) commands were given, and sets
DDT's FAKEAC flag, thereby forcing DDT to interpret memory
addresses 0-17 as DDT's own internal "registers", in which the
user's registers were saved.
<ESC><ESC>U
This command enables DDT to use actual physical addresses when
accessing memory, and clears DDT's FAKEAC flag, causing DDT to
interpret memory addresses 0-17 as the hardware registers 0-17.
This command is meaningful only when using KDDT in executive
mode, or when using FILDDT to look at the running monitor.
Although DDT accepts <ESC><ESC>U at other times, this command
then produces the same effect as <ESC>U.
The general syntax of the following virtual addressing commands is:
arg<ESC>nU
where n is the function number of the command, and arg is dependent on
the function (see the function descriptions below).
Functions 0, 1, and 2 enable you to control memory mapping by
selecting the executive process table (EPT), user process table (UPT),
or the section map through which mapping occurs. Setting a mapping
condition with any one of these functions (0, 1, and 2) also has the
effect of clearing the effects of any prior use of one of these
functions (0, 1, and 2).
You can also specify the offset into the special pages table (SPT)
with functions 0, 1, and 2 by using the following command:
arg<ESC><ESC>nU
where arg is the SPT offset, and 0<=n<=2. This form is legal only if
KL-paging is in effect.
NOTE
All forms of <ESC>B and <ESC>X are illegal if you have
used the page mapping functions (0, 1, or 2) and have
not restored standard mapping with the <ESC>U command.
11-2
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
COMMAND EXPLANATION
page<ESC>0U
This command causes memory mapping to occur through the executive
process table (EPT) that is located at physical page page.
offset<ESC><ESC>0U
This command produces the same effect as page<ESC>0U (above),
except that offset is an offset (in words) into the SPT.
page1<page2<ESC>0U
This command is an exception to the general syntax, and is legal
only under KI-paging. You can select both the user page table
(UPT) and the executive page table (EPT) with this command, where
page1 is the page number of the UPT, and page2 is the page number
of the EPT. Follow page1 with a left angle bracket (<).
page<ESC>1U
This command causes memory mapping to occur through the user
process table (UPT) that is located at physical page page. With
this command, you can bypass the EPT.
offset<ESC><ESC>1U
This command produces the same effect as page<ESC>1U (above),
except that offset is an offset (in words) into the SPT.
page<ESC>2U
This command causes mapping to occur through the section map at
physical page page. This command is legal only if KL-paging is
in effect.
offset<ESC><ESC>2U
This command produces the same effect as page<ESC>2U (above),
except that offset is an offset (in words) into the SPT. This
command is legal only if KL-paging is in effect.
11-3
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
COMMAND EXPLANATION
n<ESC>3U
This command determines whether DDT interprets references to
memory locations 0-17 as references to hardware registers, or to
DDT's own internal "registers" (which normally contain the
user-program ACs), by setting or resetting DDT's FAKEAC flag.
If n=0, reset FAKEAC flag (use the hardware registers 0-17).
If n is nonzero, set FAKEAC flag (use DDT's internal registers
0-17).
If you enter a nonzero value for n, DDT stores the value -1.
n<ESC>4U
This command tells DDT to copy hardware register block n
(0<=n<=7) to its own internal register block, set the FAKEAC
flag, and use hardware register block n as its own registers. If
the FAKEAC flag is set when you give this command, DDT first
restores the contents of its internal register block to the
hardware register block from which they were copied. This
command is legal in executive mode EDDT and KDDT only. Note that
the microcode uses register block 7, and any attempt to use this
block produces an almost immediate system crash.
addr<ESC>5U
This command copies the 20 (octal) word block located at addr to
DDT's internal "registers" and sets the FAKEAC flag.
addr<ESC>6U
This command sets the special pages table (SPT) to addr.
addr<ESC>7U
This command sets the core status table address (CST) to addr.
addr<ESC>8U
This command sets the address relocation factor to addr. DDT
adds addr to all user addresses that you enter.
addr<ESC>9U
This command read-and-write-protects all addresses above addr
(before adding relocation factor).
11-4
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
COMMAND EXPLANATION
n<ESC>10U
This command controls whether KI paging is enabled or cleared.
If n is nonzero, KI paging is enabled.
If n=0, KI paging is cleared.
If you enter a nonzero value for n, DDT stores the value -1.
| This command is illegal in executive mode EDDT.
n<ESC>11U
This command controls whether KL paging is enabled or cleared.
If n is nonzero, KL paging is enabled.
If n=0, KL paging is cleared.
If you enter a nonzero value for n, DDT stores the value -1.
| This command is illegal in executive mode EDDT.
| 22<ESC>U
| 23<ESC>U
|
| These commands specify the type of CPU on which the program is
| being debugged. 22<ESC>U refers to a KL processor. 23<ESC>U
| refers to a KS processor.
|
| For DDT, this command is meaningless, because DDT uses the
| current CPU type. However, these commands may be useful for
| FILDDT.
You can interrogate DDT to determine the last virtual addressing
command that was given for a specific function. The command:
<ESC>nU
where 0<=n<=11, returns the address of a DDT location that contains
the argument that was given if the command for that function was used,
and returns the default value if that function was not used. If you
entered a nonzero argument to a command that requires zero or nonzero
values (or if the default is nonzero), this location contains -1. You
can use DDT commands to examine this location.
11-5
PHYSICAL AND VIRTUAL ADDRESSING COMMANDS
The command:
<ESC><ESC>nU
where 0<=n<=2, returns the address of a DDT location that contains
information that indicates which function you used, and whether you
set a page address or an offset. You can use DDT commands to examine
this location. This command is illegal for all functions where n>2.
If you did not enter any commands affecting functions 0-2 since the
last <ESC>U command, the right half of this DDT location word contains
zero. Otherwise, the right half contains n+1, where n is the number
of the command function you used. If you set a page address (with
arg<ESC>nU), bit 1 of this word is reset. If you set an offset (with
arg<ESC><ESC>nU), bit 1 of the word is set.
11-6
CHAPTER 12
EXTENDED ADDRESSING
12.1 LOADING DDT INTO AN EXTENDED SECTION
If your program is loaded in a nonzero section, merge DDT with your
program with the TOPS-20 command:
@DDT
DDT is loaded into the highest-numbered free (nonexistent) section.
If your program has a TOPS-10-style entry vector in section zero, the
EXEC merges the UDDT stub into the section that contains the entry
vector, and places that section's JOBDAT symbol table pointers (.JBSYM
and .JBUSY) into the DDT locations pointed to by UDDT locations 770001
and 770002. UDDT then loads XDDT into the highest-numbered free
section. You can load DDT into a specific section with the EXEC's
/USE-SECTION switch, as:
@DDT/USE-SECTION:n
where n is the (octal) section number of a section that does not
already exist.
You can load DDT into an existing section with the /USE-SECTION and
/OVERLAY switches. You must be careful, however, that your program
does not use any pages that DDT uses. See the TOPS-20 COMMANDS
REFERENCE MANUAL for more information about the use of these switches.
12-1
EXTENDED ADDRESSING
12.2 EXAMINING AND CHANGING MEMORY
The commands /, [ (left square bracket), ] (right square bracket), !,
\ and <TAB> (see Section 4.4.3) open a memory location at an address
calculated from an expression typed in or defaulted in the command.
The syntax of the command is
{expr}{<ESC>{<ESC>}}c
where c is the command, and expr is any legal DDT expression (expr
defaults to $Q, the current quantity).
In nonzero sections, you can cause DDT to utilize all indirection and
indexing indicated by EFIWs (extended format indirect words) to
calculate 30-bit global addresses by using the format
{expr}<ESC><ESC>c
This format also recognizes and utilizes instruction format indirect
words (IFIW). These commands are thoroughly described in Chapter 4
(Displaying and Modifying Memory).
12.3 BREAKPOINTS
If DDT is running in a nonzero section, breakpoints can be set in any
section.
12.3.1 The Breakpoint Block
To set breakpoints in a section external to the one containing DDT,
DDT requires an area of contiguous storage in the section containing
the breakpoint. This area is known as the "breakpoint block". The
extra storage is required for saving global addresses for transfer of
control between your program and DDT, and also for the execution of
single-stepped instructions that reference memory locations that are
not in their section.
Each section within your program space that contains a breakpoint must
have one breakpoint block. Breakpoint blocks are located at the same
relative local address within each section (the default is 777700),
and are 100 (octal) words in size.
Each breakpoint block is always contiguous within one section.
Breakpoint blocks never extend across section boundaries and never
"wrap around" the end of a section to the beginning of the section.
12-2
EXTENDED ADDRESSING
DDT creates a breakpoint block in each section as required, if
inter-section breakpoints are enabled (see below).
You (or your program) can reference memory within a breakpoint block,
but any information stored there can be overwritten by DDT.
12.3.2 Enabling and Disabling Inter-section Breakpoints
The section-relative (18-bit) address of the breakpoint block(s) is
stored in an internal DDT location. The command <ESC>4M returns the
address of that DDT location. The symbol $4M refers to the DDT
location at the address returned by <ESC>4M. Inter-section
breakpoints are enabled as long as $4M contains the address of the
breakpoint block. At startup, DDT enables inter-section breakpoints
by default.
To change the address of the breakpoint block, enter:
n<ESC>4M
where n is the address of the breakpoint block, and can be any legal
DDT expression (20<=n<=777700). DDT uses only the right half of n,
and changes only the right half of the DDT location at $4M.
By default, the section-relative breakpoint block address is 777700,
placing the breakpoint block at the top of the section. To display
the address of the breakpoint block, enter:
<ESC>4M/
Inter-section breakpoints are disabled when $4M contains zero.
NOTE
In MDDT, $4M defaults to MDDBLK. In
KDDT, $4M defaults to EDDBLK. Each
symbol denotes the start of a 100-word
(octal) block contained in page zero of
the monitor. Page zero of the monitor
is mapped into every section that
contains monitor code.
To disable inter-section breakpoints, enter:
0<ESC>4M
12-3
EXTENDED ADDRESSING
While inter-section breakpoints are disabled, you cannot set a
breakpoint in a section external to DDT, and any breakpoints already
set in such a section are lost when you begin program execution with
<ESC>G, or continue program execution with <ESC>P. For each
breakpoint lost, DDT displays:
% CAN'T INSERT $nB - IN NON-DDT SECTION
where n is the breakpoint number.
While inter-section breakpoints are disabled, DDT cannot execute the
<ESC>X command when:
o you try to execute the instr<ESC>X command, and the default
section is not the section that contains DDT.
o you try to single-step a dangerous instruction and the
user-program PC is not in the section that contains DDT.
| In these cases, when you try to use <ESC>X, DDT rings the terminal
| bell or buzzer and sets its error message text to:
|
| Intersection reference and no $4M global breakpoint/execute block
12.4 DISPLAYING SYMBOLS IN NONZERO SECTIONS
DDT normally uses right-halfword values when searching symbol tables
for symbols to display. However, code linked in a nonzero section has
symbols defined with the section number in the left-halfword. DDT
uses a 30-bit value when searching for a symbol in the following
circumstances:
o when displaying the address of a location
o when displaying the contents of a location as an address
o when displaying the Y field of an instruction
When displaying an address, DDT searches for a symbol defined with the
30-bit value of the address. If such a symbol is not found, DDT
displays the address in halfword format.
When displaying the Y field of an instruction, DDT searches for a
symbol defined with a 30-bit value consisting of:
o the section number of the address of the word being displayed
o the section-relative address contained in the Y field of the
instruction
12-4
EXTENDED ADDRESSING
If DDT does not find a symbol defined with that 30-bit value, it looks
for a symbol defined with the 18-bit value contained in the Y field of
the instruction.
Assume a program with the following conditions:
Symbol LABL1 is defined as 0,,300
Symbol LABL2 is defined as 3,,300
Location 1,,300 contains 3,,300
Location 1,,301 contains 2,,300
Location 3,,400 contains 200040,,300
(MOVE contents of location 300 to AC 1)
When displaying the contents of location 1,,300, DDT displays:
1,,LABL1/ LABL2
When displaying the contents of location 1,,301, DDT displays:
1,,LABL1+1/ 2,,LABL1
When displaying the contents of location 3,,400, DDT displays:
LABL2+100/ MOVE 1,LABL2
12.5 DEFAULT SECTION NUMBERS
To reduce the need to type in the section number as part of the
address when you specify a location, DDT uses a default section number
when you do not specify one. DDT has two section defaulting options:
o permanent default section
o floating default section
The command <ESC>6M returns the address of an internal DDT location
that contains section default information. The symbol $6M refers to
the DDT location at the address returned by the command <ESC>6M.
When DDT is in section zero, the default section number is always
zero, regardless of the contents of $6M.
NOTE
When you use KDDT in user-mode, $6M
defaults to 0,,0. In all other cases,
$6M defaults to 1,,0.
12-5
EXTENDED ADDRESSING
12.5.1 Permanent Default Section
| If the value contained in $6M is non-negative (bit zero is reset), the
permanent default section option is in effect. DDT then takes the
left half of $6M as the section number of any address that you type in
without a section number.
Set the permanent default section by entering:
n,,0<ESC>6M
where n is the section number, and can be any legal DDT expression.
12.5.2 Floating Default Section
If the value contained in $6M is negative (bit zero is set), the
floating default section option is in effect. This is the default
option (at start-up, DDT initializes $6M to -1). DDT selects the
floating default section as follows:
o If you enter DDT from its normal start address, DDT sets the
default section to:
> the section that contains the program entry vector (if
there is one) OR
> section zero.
o If you enter DDT from a breakpoint, DDT sets the default
section to the section that contains the breakpoint.
o If you open a local address between 20 and 777777, DDT sets
the default section to the section that contains the open
address.
o If you type in an address that contains a section number
(including a symbol that is defined with a section number),
DDT sets the default section to the one in the address you
entered.
If you exit DDT with <CTRL/C> or <CTRL/Z>, and then reenter DDT, the
current location does not change. If you give a command that takes
the current location as its default address argument, DDT sets the
floating default section to the section of the current location.
In the following example, the DDT screen display is on the left, and
explanatory comments are on the right. The entry vector is in
section 1. Symbol START is not defined with a section number. User
input is in lowercase.
12-6
EXTENDED ADDRESSING
SCREEN DISPLAY USER INPUT EXPLANATION
3,,place/ Examine location 3,,PLACE.
LABL1 DDT displays the contents.
<LF> Type in <LF> to examine
the next location.
3,,PLACE+1/ LABL1+2 DDT displays the next
location. The floating
default section = 3.
<CTRL/C> Exit with <CTRL/C>.
The current location is
3,,PLACE+1.
@ TOPS-20 prompts you.
@ddt Reenter DDT.
DDT DDT is loaded and ready
for your command. The
floating default section is
1, because the entry vector
is in section 1.
<LF> Type in <LF> to examine
the next location.
3,,START+2/ LABL1+4 DDT displays the address
and contents of the next
location. DDT doesn't use
the floating default section,
because your <LF> command
defaults addr to the current
location, and uses its
section number (3).
start/ Examine location START.
DDT uses the floating default
section number because symbol
START is defined with no
section number.
JFCL 0 DDT displays the contents.
<LF> Type in <LF> to examine
the next location.
1,,START+1/ MOVE 1,LABL1 DDT displays the address
and contents of the location.
12-7
EXTENDED ADDRESSING
12.6 EXECUTING SINGLE INSTRUCTIONS
Instructions that are executed by means of the command
instr<ESC>X
where instr is the instruction for DDT to execute, are executed within
the current default section. If that section is not the one that
contains DDT, DDT uses the breakpoint block in that section to execute
instr. If the floating default section option is in effect and you
are unsure of the current default section, use the addr/ command to
open a location in the section in which you wish DDT to execute instr.
This sets the default section to the section specified by addr.
If DDT is to execute the instruction in a section other than the one
that contains DDT, inter-section breakpoints must be enabled.
If you try to execute instr outside DDT's section while intersection
breakpoints are disabled, DDT sounds the terminal buzzer or bell,
displays "?" and sets its error string to:
| Intersection reference and no $4M global breakpoint/execute block
12.7 ENTERING PATCHES IN EXTENDED SECTIONS
You cannot enter a patch if a patching area does not exist in the
section that contains the word to be replaced. To ensure that there
is a patching area for each section that contains user-program code,
do one of the following:
o reserve the same part of each section for patches, and define
the patch symbol as 0,,addr, where addr is the local address
of the patching area
o use only one patching area and map it into all the sections
that contain user-program code. Define the patch symbol as
0,,addr, where addr is the local address of the patching
area.
o define a different symbol for each section's patching area,
and use the symbol appropriate to the section being patched
If the left half of expr is zero, DDT defaults the section to the
section that contains the open location. If the left half of expr is
a value that is not the section that contains the open location, DDT
displays:
?CAN'T PATCH ACROSS SECTIONS
12-8
APPENDIX A
ERROR MESSAGES
DDT and FILDDT display error messages to indicate the results of your
commands. DDT sometimes (and FILDDT usually) displays these messages
on the screen, and at other times displays only a question mark. When
only a question mark is displayed, a location internal to DDT usually
points to a text string that is the error message. To display the
error message, enter the command:
<ESC>?
o
Following is a list of DDT messages together with explanations of what
the messages indicate.
? ABOVE PROTECTION REGISTER LIMIT
The address of the location you tried to display or modify is
above the protection register limit, which is set by n<ESC>9U.
? ACTUAL REFERENCE FAILED
A memory reference failed unexpectedly (the page exists and is
readable, but the reference failed anyway).
? ADDRESS GREATER THAN 777777
An address to be mapped through a section table has a nonzero
section number. This can occur only if you specified a section
table with the n<ESC>{<ESC>}2U command.
A-1
ERROR MESSAGES
| ? ADDRESS BEYOND END OF PHYSICAL MEM
|
| You attempted to examine a physical memory location beyond the
| end of physical memory. This error occurs only if you have used
| the <ESC><ESC>U command to enable physical addressing.
? Bad format for .EXE file
You specified a file that appears to have an .EXE directory, but
the directory is badly formatted or DDT cannot read it because of
some other reason.
? BAD $4M VALUE
You used the n<ESC>4M command where 777700<n<20.
? BAD POINTER ENCOUNTERED
DDT does not recognize the type code contained in a page map
pointer. This can occur only if you are trying to do your own
virtual address mapping, and used the expr<ESC>{<ESC>}nU command,
where 0<=n<=2.
? CAN'T BE WRITE ENABLED
Even though you have automatic write-enable turned on, DDT is
unable to write-enable a page that exists and is write-protected.
? CAN'T CREATE PAGE
DDT attempted to create a page and failed, or else cannot attempt
to create the page (see the <ESC>1W command).
? CAN'T DEPOSIT INTO SYMBOL TABLE BECAUSE .....
You tried to define or kill a symbol, but DDT was unable to
modify the symbol table. Look up the second part of the error
message in this appendix.
? CAN'T DEPOSIT INTO SYMBOL TABLE BECAUSE DEPOSIT FAILED
You tried to define or kill a symbol, but DDT was unable to
modify the symbol table, and cannot identify the specific reason.
A-2
ERROR MESSAGES
% CAN'T INSERT $nB BECAUSE .....
DDT is not able to access the location where you inserted your
breakpoint. Look up the second part of the error message in this
appendix. This situation occurs before DDT tries to execute
<ESC>G, <ESC>P, <ESC>X, or <ESC><ESC>X.
% CAN'T INSERT $nB BECAUSE BREAKPOINT IS IN DIFFERENT SECTION
DDT is not able to access the location where you inserted your
breakpoint because inter-section breakpoints are not enabled
(<ESC>4M contains zero). This error occurs before DDT tries to
execute <ESC>G, <ESC>P, <ESC>X, or <ESC><ESC>X. To enable
inter-section breakpoints, deposit the breakpoint block address
in the location addressed by the command <ESC>4M.
% CAN'T INSERT $nB BECAUSE MEM REF FAILED
DDT is not able to access the location where you inserted your
breakpoint. DDT is not able to identify the reason. This occurs
before DDT tries to execute <ESC>G, <ESC>P, <ESC>X, or
<ESC><ESC>X. A typical occurrence is when you have a breakpoint
set in the swappable monitor (set in KDDT in executive mode), but
the swappable monitor is not locked in memory.
? CAN'T PATCH ACROSS SECTIONS
You tried to insert a patch in a section other than the one that
contains the patching area.
? CAN'T PEEK PHYSICAL
You attempted to PEEK at the monitor but have specified other
than normal virtual addressing (FILDDT only).
% CAN'T REMOVE $nB BECAUSE .....
DDT is not able to access the location where you inserted your
breakpoint. Look up the second part of the error message in this
appendix. This error occurs when your program enters DDT from a
breakpoint.
A-3
ERROR MESSAGES
% CAN'T REMOVE $nB BECAUSE BREAKPOINT IS IN DIFFERENT SECTION
DDT is not able to access the location where you inserted your
breakpoint. because inter-section breakpoints are not enabled
(<ESC>4M contains zero). This error occurs when your program
enters DDT from a breakpoint. To enable inter-section
breakpoints, deposit the breakpoint block address in the location
addressed by the command <ESC>4M.
% CAN'T REMOVE $nB BECAUSE MEM REF FAILED
DDT is not able to access the location where you inserted your
breakpoint. DDT is not able to identify the reason. This error
occurs when your program enters DDT from a breakpoint. A typical
occurrence is when you have a breakpoint set in the swappable
monitor (set in KDDT in executive mode), but the swappable
monitor is not locked in memory.
% CAN'T SET BREAKPOINT, $4M NOT SET
You attempted to set a breakpoint in a section other than the one
containing DDT while inter-section breakpoints were not enabled.
| ? FAILURE ON SWITCHING ADDRESS SPACE
|
| EDDT (Executive mode EDDT only) encountered an error while trying
| to access the virtual address space where monitor symbols are
| kept.
? Garbage at end-of-command
FILDDT encountered extra text at a place in the command where
there should have been only <RET>.
|
|
| Intersection reference and no $4M global breakpoint/execute block
|
| Inter-section breakpoints are not enabled, and one of the
| following is true:
|
| o you tried to execute the command instr<ESC>X but the default
| section is not the section that contains DDT.
|
| o you tried to single-step a dangerous instruction but the
| user-program PC is not in the section that contains DDT.
A-4
ERROR MESSAGES
? I/O error
Some kind of I/O error occurred when FILDDT attempted to read or
write to the unit specified in a DRIVE or STRUCTURE command.
? Illegal channel number
You entered a DRIVE command that contained an illegal channel
number.
? Illegal controller number
You entered a DRIVE command that contained an illegal controller
number.
? Illegal unit number
You entered a DRIVE command that contained an illegal unit
number.
? Incorrect symbol table pointer
FILDDT is unable to read the symbol table specified by the symbol
table pointer in the file.
? Input device must be a disk
The device you specified is not a disk.
? Insufficient memory to read EXE file directory
FILDDT does not have enough free memory to read in the directory
section of the .EXE file that you specified.
A-5
ERROR MESSAGES
? Insufficient memory to read PDV list
FILDDT does not have enough free memory to read in the list of
PDVs in the .EXE file that you specified.
NOTE
FILDDT sometimes runs out of memory
when you use the <CTRL/E> command
to save files without exiting
FILDDT. If this is the case, exit
with the <CTRL/Z> command, and then
restart FILDDT with the TOPS-20
FILDDT command.
? INVALID DDT INTERNAL ADDRESS
You addressed an internal location that is not defined. This is
most likely to occur after you use a command that returns a value
(such as <ESC>M) to examine a DDT location and then use <LF> or
<BKSP> to look at nearby memory.
? Invalid file specification, message
where message is a TOPS-20 error string. FILDDT could not parse
a filespec given to a LOAD or GET command.
? Invalid guide phrase input
where input is a guide (or noise) phrase that you typed in, and
does not match FILDDT's guide phrase.
M
You entered a symbol that is defined in more than one module.
You can select the correct symbol by opening the symbol table
associated with that module, using the command module<ESC>:.
? MDDT BREAKPOINT BLOCK ALREADY IN USE
Only one fork may have breakpoints set in MDDT at one time. You
attempted to set a breakpoint in MDDT while another fork had
already set an MDDT breakpoint.
A-6
ERROR MESSAGES
? Missing or extra units in structure
The number of units with the name supplied in a STRUCTURE command
does not agree with the number of units in the first structure
with that name returned by MSTR%.
? No keyword input
where input is a word that you typed in. You entered ENABLE
without the DATA, PATCHING, or THAWED qualifier.
? NO READ ACCESS
You tried to display a word in a page to which you do not have
read access.
? No such command as input
where input is a word that you typed in. You entered a command
that FILDDT does not recognize.
? No such file structure
COMND% and DEVST% think you supplied a disk name in a STRUCTURE
command, but no unit with that name was returned by MSTR%.
? Not enough memory for file pages
FILDDT does not have enough free memory for its file page
buffers.
NOTE
FILDDT sometimes runs out of memory when you use
the <CTRL/E> command to save files without
exiting FILDDT. If this is the case, exit with
the <CTRL/Z> command, and then restart FILDDT
with the TOPS-20 FILDDT command.
? Not enough memory for symbols
FILDDT does not have enough free memory to read in the symbol
table from the specified .EXE file. See the note above.
A-7
ERROR MESSAGES
? NOT IN CORE
You tried to map through a page map pointer (in a UPT, SPT, or
section table) that addresses a page that is swapped out. This
can occur only if you are trying to do your own virtual address
mapping, and used the expr<ESC>{<ESC>}nU command, where 0<=n<=2.
% Not in .EXE format -- Data file assumed.
A GET command without a /DATA switch or a previous ENABLE
DATA-FILE command specified a file which is not in .EXE file
format. FILDDT assumes it is a data file.
? NOT WRITABLE
You tried to modify a word in a write-protected page. To enable
writing on protected pages, use the <ESC>0W command.
|
|
| ? Null filename illegal
|
| You did not enter a file specification to a command that requires
| one.
? PAGE DOES NOT EXIST
You tried to display a word in a nonexistent page.
? Patching is not enabled
You attempted to modify (with FILDDT) a file, a disk, or the
monitor, but did not use the /PATCH switch or the ENABLE PATCHING
command.
% Patching the running monitor is illegal
You entered an ENABLE PATCHING command and then gave a PEEK
command.
? PEEK FAILED
You tried to PEEK at the monitor, but do not have WHEEL or
OPERATOR privileges enabled.
A-8
ERROR MESSAGES
% Symbols cannot be extracted from a data file
You used the command GET filnam/SYMBOL. Either the file
specified by filnam is not an .EXE file, or you previously used
the command ENABLE DATA-FILE.
? Symbols cannot be extracted from a data file
You used the command LOAD filnam, and the file specified by
filnam is not an .EXE file.
U
You entered a symbol that DDT cannot locate in any symbol table.
Cure this by entering the correct symbol, or by defining the
symbol with the command {expr<}symbol:.
? UNEXPECTED MOVEM FAILURE
DDT could not deposit to memory even though the page exists
exists and is write-enabled.
NOTE
In the following messages, unit is one of the
following:
o "Unit" (if you used the DRIVE command)
o "Unit u on controller k on channel c" (if you
used the STRUCTURE command, where u, k, and c
are the arguments you entered)
% Unit has a bad BAT block
The unit that you specified in a DRIVE or STRUCTURE command has a
bad BAT block.
% Unit has a bad HOME block
The unit that you specified in a DRIVE or STRUCTURE command has a
bad HOME block.
A-9
ERROR MESSAGES
? Unit is off line
The unit that you specified in a DRIVE or STRUCTURE command is
off line.
% Unit is write locked
You used an ENABLE PATCHING command and then specified a
write-locked unit in a DRIVE or STRUCTURE command.
% Update of file's symbol table failed
FILDDT was unable to write the modified symbol table back to the
file after you gave a <CTRL/Z> or <CTRL/E> command. This may
also occur when you use the n<ESC>5M command.
A-10
GLOSSARY
bit
Bit is a contraction of "binary digit". A bit is the smallest
unit of information in a binary system of notation. It is the
choice between two possible states, usually designated as zero
and one. Bits of data are often used as flags to indicate
on/off or yes/no conditions.
breakpoint
A breakpoint is a location in a program's executable code that
has been modified so that if the program attempts to execute
the instruction at that location, control passes to DDT before
the instruction is executed.
current display mode
The current display mode is the mode in which DDT displays the
next word (unless there is an intervening command that changes
the current display mode). Also known as the current typeout
mode.
current quantity
The current quantity is the most recent of:
o the last 36-bit quantity that DDT displayed
o the 36-bit evaluation of the last expression that you
entered as an argument to a command that deposits to memory
This value is often used as the default argument for the next
command. Also known as the last value typed.
Gloss-1
GLOSSARY
current location
The current location is a memory word that has been referenced
by an earlier DDT command. The address of the current location
is the default address for most DDT commands.
current location stack entry
The location that will become the current location as a result
of the next <ESC><RET> command.
current radix
The current radix is the radix in which DDT displays numeric
values.
current typeout mode
See current display mode.
debugging
Debugging is the process of finding and removing programming
errors from programs.
EDDT
EDDT is the DDT variant that is used to debug executive-mode
programs.
FILDDT
FILDDT is the DDT variant that is used to examine and modify
disk files and disk structures. FILDDT is also used to examine
(but not modify) the running monitor.
jiffy
A jiffy is a unit of time defined as one AC (alternating
current) cycle. If your line power has a frequency of 60 Hz.,
a jiffy is one sixtieth of a second (about 16 milliseconds).
If your line power has a frequency of 50 Hz., a jiffy is one
fiftieth of a second (20 milliseconds).
KDDT
KDDT is the DDT variant used to debug the monitor. You can set
breakpoints, single-step instructions, and perform any other
DDT function.
Gloss-2
GLOSSARY
last value typed
See current quantity.
location
A location is a numbered or named place in storage or memory
where a unit of data or an instruction can be stored. This
manual also uses the terms word and memory word.
location counter
The location counter is a memory word that contains the address
of the current location.
location sequence stack
The location sequence stack is a stack in which DDT stores the
addresses of locations used earlier. DDT uses the stack to
access these locations again without having you explicitly
enter the address of each of the locations. DDT references
these addresses in a last-in, first-out manner.
MDDT
MDDT is the DDT mode used to examine and patch the running
monitor.
open location
The open location is a memory word that you can modify with
your next DDT command.
prevailing display mode
The prevailing display mode is a user-defined default display
mode. DDT displays memory words in the prevailing mode unless
you specify a temporary display mode. You can restore the
prevailing mode with the <RET> command. See Chapter 4
(Displaying and Modifying Memory) for a list of other commands
that restore the prevailing display mode.
reset
Reset refers to the zero condition of a bit or flag. A bit
that is zero is said to be reset. To reset is the verb that
refers to the act of turning the bit off, "clearing" the bit,
or making it zero.
Gloss-3
GLOSSARY
set
Set refers to the nonzero condition of a bit or flag. A bit
that is nonzero is said to be set. To set is the verb that
refers to the act of turning the bit on, or making it nonzero.
single-stepping
Single-stepping is the process of executing program
instructions one at a time using DDT, to verify the result of
each instruction.
target
Target refers to the contents of the virtual address space that
FILDDT is accessing. The virtual address space may contain a
disk structure, a disk file, or the running monitor.
temporary display mode
The temporary display mode is a short-term, user-selected
display mode which overrides the prevailing display mode.
Temporary display mode remains in effect until you enter <RET>
or <TAB>. Also known as the temporary typeout mode.
temporary typeout mode
See temporary display mode.
Gloss-4
INDEX
$, 2-2 ], 4-9, 4-12, 4-13, 4-15,
$$., 5-2, 5-3 12-2
$., 5-2, 5-3 ^, 4-9
Backslash, 4-9, 4-12, 4-13,
ASCIZ strings, 4-19 4-16, 12-2
Automatic page-creation, 4-21 <BKSP>, 2-3, 4-9
Automatic proceed <CTRL/U>, 2-3
terminating, 5-8 <CTRL/Z>, 2-3
Automatic proceed flag, 5-7 deleting, 2-3
Automatic write-enable, 4-20 Equal sign, 4-6
<ESC>, 2-3, 4-12
BACKSPACE key, 2-3 <ESC>", 3-6
<BKSP>, 2-3 <ESC>"5, 3-7
$0BPT, 5-10 <ESC>"c<ESC>, 3-7
Breakpoint block, 12-2 <ESC>., 5-2
Breakpoints, 2-5, 5-1 <ESC>0<, 8-6
conditional, 5-9 <ESC>0T, 4-5
DDT action at, 5-3 <ESC>1:, 7-2
display additional location at, <ESC>1M, 4-23, 4-25
5-4 <ESC>1S, 4-5
display address of, 5-6 <ESC>1W, 4-21
executing command strings at, <ESC>2M, 4-3
5-5 <ESC>3M, 4-3
executing instructions at, 5-11 <ESC>4M, 12-3
executing subroutines at, 5-13 <ESC>5M, 7-6
inter-section, 12-3 <ESC>5T, 4-5
proceeding from, 5-3, 5-6 <ESC>6M, 12-5
removing, 5-6 <ESC>6T, 4-5
setting, 5-3 <ESC>7T, 4-5
single-stepping at, 5-11 <ESC>:, 7-1, 7-2
unsolicited, 5-10 <ESC><, 8-1
Byte pointers, 4-6 <ESC><BKSP>, 4-11, 4-12
<ESC><ESC>., 5-2
<ESC><ESC>1:, 7-7
Commands <ESC><ESC>1W, 4-21
DDT <ESC><ESC>1X, 5-15
, 4-6 <ESC><ESC>:, 7-6
!, 4-9, 4-12, 4-13, 4-16, <ESC><ESC><, 8-3
4-17, 4-18, 12-2 <ESC><ESC>K, 7-3
", 3-5 <ESC><ESC>nU, 11-2
""<""">, 3-6 <ESC><ESC>P, 5-8
., 4-7 <ESC><ESC>Q, 4-8
/, 4-9, 4-12, 4-13, 4-14, <ESC><ESC>U, 11-2
12-2 <ESC><ESC>W, 4-20
;, 4-6 <ESC><ESC>X, 5-14, 5-16
=, 4-6 <ESC><LF>, 4-11
?, 4-19, 4-23, 5-14, 6-3, 7-5 <ESC><RET>, 4-11
[, 4-9, 4-12, 4-13, 4-14, <ESC>>, 8-2
12-2 <ESC>?, 2-3
\, 4-9, 4-12, 4-13, 4-16, <ESC>B, 5-6, 11-2
12-2 <ESC>C, 4-5
Index-1
<ESC>D, 7-3 DDT variants, 1-2
<ESC>E, 6-3 Default section
<ESC>F, 4-5 floating, 12-6
<ESC>G, 5-1, 5-6, 5-16, 11-1 permanent, 12-6
<ESC>H, 4-5 Display mode
<ESC>I, 5-16 C, 4-5
<ESC>K, 7-3 current, 4-3
<ESC>M, 6-4 F, 4-5
<ESC>N, 6-2 H, 4-5
0<ESC>nB, 5-6 O, 4-5
<ESC>nB, 3-4, 5-3, 5-4, 5-6 prevailing, 4-2
<ESC>nI, 3-4 1S, 4-5
<ESC>nM, 3-4 S, 4-5
<ESC>nT, 4-5 symbolic, 4-1
<ESC>nU, 3-4, 11-2 0T, 4-5
<ESC>O, 4-5 5T, 4-5
<ESC>P, 5-6, 5-7, 5-16, 11-1 6T, 4-5
<ESC>Q, 4-8 temporary, 4-2
<ESC>S, 4-5
<ESC>U, 5-17, 11-2 EFIW, 4-13, 4-18
<ESC>V, 4-23 <ESC>, 2-2, 2-3
<ESC>W (search), 6-1 ESCAPE key, 2-2, 2-3
<ESC>W (write-protect), 4-20 Expression operators, 3-7
<ESC>X, 5-11, 5-13, 5-16, Expressions, 3-2
11-1, 11-2 Extended format indirect word,
<ESC>Z, 4-19 4-13
Exclamation point, 4-9, 4-12,
4-13, 4-16, 4-17, 4-18, IFIW, 4-13, 4-18
12-2 Initializing memory, 4-19
Left square bracket, 4-9, Input
4-12, 4-13, 4-14, 12-2 ASCII character, 3-6
<LF>, 2-3, 4-9 ASCII string, 3-5
Period, 4-7 decimal integer, 3-3
<RET>, 2-3, 4-9, 4-10 floating point, 3-3
Reverse slash, 4-9, 4-12, halfwords, 3-10
4-13, 4-16, 12-2 instructions, 3-10
Right square bracket, 4-9, long text string, 3-4
4-12, 4-13, 4-15, 12-2 octal integer, 3-2
Semicolon, 4-6 RADIX50 word, 3-7
Slash, 4-9, 4-12, 4-13, 4-14, SIXBIT character, 3-7
12-2 SIXBIT string, 3-6
<TAB>, 2-3, 4-9, 4-12, 4-13, text, 3-4
4-17, 12-2 value returned by a command,
Underscore, 4-6 3-3
<ESC>L (page access), 4-22 Input to DDT, 3-2
FILDDT Instruction format indirect word,
<CTRL/Z>, 9-9 4-13
CONTROL key, 2-3
CPU type for FILDDT, 11-5 Last quantity typed, 4-8
Current display mode, 4-3 <LF>, 2-3
Current location, 2-4, 4-7 LINE FEED key, 2-3
Current location stack entry, 4-8 Location counter, 2-4, 4-7
Current quantity, 2-4, 4-8 Location sequence stack, 2-4, 4-8
Dangerous instructions, 5-15 $4M, 12-3
Index-2
$5M, 7-6 for address, 6-3
$6M, 12-5 for matching value, 6-1
Mask for non-matching value, 6-2
output byte size, 4-3 terminate, 6-3
search, 6-4 Search mask, 6-4
TTY control, 4-23 Single-stepping, 5-11
Maximum symbolic offset, 4-4 Symbol table
Memory protection, 4-20 closing, 7-2
Memory watch, 4-23 finding name of, 7-2
opening, 7-1
$nB, 5-2 Symbolic debugging, 1-1
Symbols
Open location, 2-4, 4-7 creating undefined, 7-4
Operators defining new, 7-2
in expressions, 3-7 deleting, 7-3
Output byte size mask, 4-3 listing specific, 7-5
listing undefined, 7-5
Page accessibility, 4-22 locating, 7-4
Patch multiply-defined, 7-1
abort, 8-6 reactivating typeout of, 7-3
before instruction, 8-1 redefining old, 7-2
following instruction, 8-3 suppressing typeout of, 7-3
terminate, 8-2, 8-3 TAB key, 2-3
Prevailing display mode, 4-2 <TAB>, 2-3
Proceed count, 5-7 Temporary display mode, 4-2
TTY control mask, 4-23
$$Q, 4-8
$Q, 4-8 Unsolicited breakpoint, 5-10
User-program context, 5-16
<RET>, 2-3
RETURN key, 2-2, 2-3 Watching memory, 4-23
Search Zeroing memory, 4-19
Index-3