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DEBUGGING SIMULA PROGRAMS WITH SIMDDT
SIMDDT is an interactive program that is used to debug SIMULA programs.
SIMDDT allows the user to:
a) set up to 20 breakpoints in the program [STOP] AT [module:] nn ...
b) continue from a breakpoint PROCEED
c) display the current breakpoint settings [STOP] BREAKS
d) remove a breakpoint setting REMOVE [AT n]
e) change the contents of a variable INPUT x:= ...
f) display the contents of a variable OUTPUT x, ...
g) display all variables in the storage pool VARIABLES [/switches]
h) display the dynamic operating chain CHAIN
i) display all scheduled processes SCHEDULED
k) switch output to a disk file e.g. a.bug USE a.bug
l) display the source code DISPLAY [module:][m:n!m,n]
m) move SIMDDT viewpoint : to object x INSPECT x
to SIMDDT interrupt point INSPECT/START
to CLASS or PROCEDURE generation point INSPECT/RETURN
to viewpoint before last RETURN INSPECT/RESET
to statically enclosing block INSPECT/UP
n) close open files [STOP] CLOSE
o) read SIMDDT control file e.g. x.cmd @x.cmd
p) terminate execution EXIT
1. LOADING AND STARTING SIMDDT
The SIMDDT program is self-relocating and it is read from disk by a
SIMRTS routine when requested. The SIMULA compiler switches I
(IDENTIFICATION, produces a line number table) and D (DEBUGS, produces a
symbol table) must have been set during compilation if the program is to
be debugged with SIMDDT. The switches are set by default but if they
were set off, SIMDDT will give incomplete information to the user.
If the source file has extension SIM or the /SIMULA switch is used,
the DEBUG monitor command will ensure that SIMDDT is read into low
segment core and started before the SIMULA program execution
1.2 LOAD, SAVE, GET, REENTER
The monitor commands LOAD plus SAVE will save the user program not
including SIMDDT on disk. If issued directly after LOAD (+SAVE) or
GET, the REENTER command will cause SIMDDT to be read into low
segment core and started. The START monitor command will start
user program execution directly.
1.3 ^C - REENTER
After the SIMULA program has started to execute without the
debugging system it is usually possible to invoke SIMDDT. One or
two ^C commands will stop execution and return the terminal to
monitor mode. The REENTER monitor command will load and start
SIMDDT, which will give the number of the source program line which
corresponds to the statement which was interrupted by ^C. This is
very useful when the program is looping. ^C can also be used if
SIMDDT is already loaded.
1.4 Program errors
SIMDDT will be called to write the error message and information on
where the error occurred.
1.5 CONTINUE after program exit
The CONTINUE monitor command can be used to start SIMDDT after a
normal program exit. The variables in the storage pool can be
displayed with the VARIABLES command.
1.6 REENTER after program exit
The REENTER command should be used to restart the program and
SIMDDT after program exit. Note that all breakpoint settings will
be lost, since the data area is reinitialized. If SIMDDT was not
loaded at execution start, the START command will restart the
program without invoking SIMDDT.
2 SIMDDT COMMANDS
SIMDDT operates in two modes, debug and error mode. SIMDDT is in error
mode when entered after a program error, otherwise it is in debug mode.
2.1 Command syntax
SIMDDT will translate all lower case letters to upper case. The
reserved words in the commands can be truncated to any number of
characters as long as they are unique. The keywords INPUT and STOP
have also been given short forms namely I and ST. A command may
not occupy more than one line.
A line starting with the character ; will be treated as a comment
The user identifies a breakpoint with a source program line number.
In the command descriptions below the notation <LINE> is used.
<LINE> has the form [<MODULE>:] <NNNNN>.
<MODULE> is MAIN or the SIMULA name of a separately compiled
procedure or class. MAIN indicates the main program. If <MODULE>:
is omitted, the current module is used by SIMDDT, that is MAIN at
program start and later the module in which the current breakpoint
<NNNNN> is a line number in the source program. The line should
contain the beginning of an executable statement. If not found the
first higher numbered line on which a statement starts will be
In the commands the user references a source variable with the
notation <IDENTIFICATION> or <IDENTIFICATION2>.
<IDENTIFICATION> ::= <IDENTIFICATION1>
[QUA <CLASS IDENTIFIER>] !
<IDENTIFICATION1> ::= <IDENTIFIER> !
THIS <CLASS IDENTIFIER>!
<ARRAY IDENTIFIER>(<SUBSCRIPT LIST>)
<SUBSCRIPT LIST> ::= [-] <INTEGER> !
[-] <INTEGER>,<SUBSCRIPT LIST>
<IDENTIFICATION2> ::= <IDENTIFICATION> !
[<IDENTIFICATION>.]<ARRAY IDENTIFIER> !
The <IDENTIFIER> must be a simple variable of type INTEGER, REAL,
LONG REAL, BOOLEAN or CHARACTER or a simple object reference or
TEXT type variable. When the <IDENTIFIER> is a formal parameter
called by name it is not handled by SIMDDT. A formal parameter
with transmission mode by value or by reference will be treated
like a declared variable. The standard procedures SYSIN, SYSOUT,
FIRST, LAST, SUC, PRED, PREV, EVTIME, MAIN, TIME and CURRENT are
accepted by SIMDDT. A type procedure identifier is handled by
SIMDDT if the current block is the procedure block. The identifier
can however not be used in connection with the IFCHANGED and the IF
features in a breakpoint command or on the right hand side in an
The brackets ( ) around the <SUBSCRIPT LIST> can be replaced by a
pair of square brackets, e.g. A[1,2].
In the commands below the notation <STRING> is used. <STRING> is a
string of characters enclosed in " . The first 5 characters in the
string are part of the message that SIMDDT outputs at the
[STOP] AT <LINE> [,<N>] [<STRING>]
SIMDDT ACTION: Identifies a breakpoint and outputs a message every
n:th time the referenced statement is executed. If STOP is given
execution is halted and new SIMDDT commands are accepted. <N>, the
loop counter, is an integer number.
[STOP] AT <LINE> [<STRING>] [IFCHANGED] <IDENTIFICATION2> [,
SIMDDT ACTION: Identifies a breakpoint. If IFCHANGED is specified
SIMDDT will output only changed variable values, otherwise the
values are always given. If IFCHANGED is specified the first time
the breakpoint is reached, the value is compared to 0, FALSE,
NOTEXT, NONE or CHAR(0), depending on its type. * the complete
block indicator and <ARRAY IDENTIFIER> are not allowed when
[STOP] AT <LINE> [<STRING>] IF <IDENTIFICATION>
<RELATION OPERATOR> <VALUE>
SIMDDT ACTION: Identifies a breakpoint. SIMDDT will output the
variable value if the relation is TRUE.
The <RELATION OPERATOR> can be one of > >= < <= = \= == =/= GT GE
LT LE EQ NE EQV IS IN. The <VALUE> can be an <IDENTIFICATION>,
TRUE, FALSE, NOTEXT, NONE, arithmetic constant, character constant,
text value constant or CLASS identifier.
REMOVE [ AT <LINE> ]
SIMDDT ACTION: Remove all breakpoint commands for a specific line
or remove all breakpoints.
SIMDDT ACTION: List all breakpoint commands. The input order is
not kept. If STOP is specified, SIMDDT will halt after each
breakpoint command and allow the user to remove it. When all
breakpoint commands for a line are removed the breakpoint is
OUTPUT <IDENTIFICATION2> [/-TEXT][/-ARRAY]
SIMDDT ACTION: Output the values of the variables. See VARIABLES
for explanation of the switches.
INPUT <IDENTIFICATION> <ASSIGNMENT OPERATOR> <VALUE>
SIMDDT ACTION: Changes the value of the referenced variable to the
value given in the command. The operators are := and :-. See
above for explanation of <VALUE>.
<RANGE> ::= <NNNNN> ! [<NNNNN>]:<NNNNN> ! [<NNNNN>],<NN>
SIMDDT ACTION: Output the indicated source program lines.
INSPECT <IDENTIFICATION> ! /START ! /RETURN ! /RESET ! /UP
SIMDDT ACTION: The point in the program, from which SIMDDT sees
the variables, is moved. This makes it possible to input and
output variables, which are not visible from the block in which the
program execution was interrupted.
SIMDDT will now see inside the CLASS object, to which the variable
refers. It must be an object reference (not NONE).
SIMDDT will again see from the place, where program execution was
originally interrupted and SIMDDT entered. If SIMDDT was entered
via an error or via ^C-REENTER, the initial SIMDDT message is
repeated, giving the reason for entering SIMDDT. Useful with
SIMDDT should be looking inside a procedure or an active CLASS.
/RETURN will make SIMDDT see from the point where the procedure was
called or where the class was generated or called.
Go back to where SIMDDT was looking before the last INSPECT /RETURN
Look directly at the statically enclosing block.
SIMDDT ACTION: SIMDDT will either start program execution or
continue processing at the point where it was interrupted. PROCEED
is not valid after an error from which it is not possible to
continue or after a NOPROCEED command.
USE <FILE SPECIFICATION>
SIMDDT ACTION: SIMDDT output will be written on the file specified
in the command. All output that signals a user action is also
output on TTY e.g. the message "STOP AT MAIN:17 " will be output
both at the TTY and the file at the breakpoint stop. The file is
not closed until a new USE command is given or at the end of
execution. The format of the <FILE SPECIFICATION> is the same as
the one used for the other user files, see chapter 8.2. USE TTY:
will reset SIMDDT output to the terminal.
SIMDDT ACTION: Writes the dynamic operating chain starting with
the current block. Only procedures, class instances and inspected
class instances are given. The name of the block and its
activation line are listed.
SIMDDT ACTION: The complete storage pool is scanned and all
variables that are of a type treated by SIMDDT are listed together
with the name of the dynamic block in which the variables are
declared. Unless /-GC was specified or garbage collection is not
safe, the garbage collector routine (G.C.) will be called before
the storage pool is scanned. When /-ARRAY is specified all array
elements are skipped in the output. When /-TEXT is specified all
text characters are skipped in the output. To reduce output only
variables which do not have their initial values are given. The
amount of data is often very large, and the USE command can be used
to direct the output to a disk or LPT file.
SIMDDT ACTION: For each scheduled process the following will be
EVTIME= scheduled time
Octal address of dynamic area DETACHED <LINE>
ALL [/-ARRAY] [/-TEXT] [/-GC] [/START:[-]<oooooo>]
SIMDDT ACTION: Produces the same information as if the commands
CHAIN, VARIABLES and SCHEDULED had been given. The switches apply
to the implied VARIABLES command, q.v.
SIMDDT ACTION: Lists and closes all open files except SYSIN and
SYSOUT. If STOP is specified SIMDDT will halt and allow the user
to close the file. Answer CLOSE or carriage return.
SIMDDT ACTION: Inhibits the use of the PROCEED command. After
this command it will be possible to use a critical command such as
USE or DISPLAY. Not necessary when stopping at preset breakpoints.
@ <FILE SPECIFICATION>
SIMDDT ACTION: SIMDDT input will be read from the file specified
in the command. The command will be output on the TTY before it is
processed. When end of file found SIMDDT will request input from
SIMDDT ACTION: Returns control to SIMRTS which closes the SYSIN
and SYSOUT files and then returns to the monitor.
SIMDDT ACTION: Lists part of the SIMDDT.HLP file.
2.3 Command examples
STOP AT 55,3
EXPLANATION: Set a breakpoint at first statement on line 55 and
stop processing every third time the statement is executed so that
the user can communicate with SIMDDT.
AT MAIN:30 "LIST" VINT[1,3], VREF.VBOOL
EXPLANATION: Output the values of the variables VINT[1,3] and
VREF.VBOOL each time the first statement on line 30 in the main
program is to be executed. The message will contain the letters
AT 10 IFCHANGED VREAL,VTEXT
EXPLANATION: Output the variable value if any of the variables
were changed since the last time the statement at line 10 was to be
STOP AT 80 IF VREAL>=1.5
EXPLANATION: Stop execution at the statement on line 80 if the
INPUT VTEXT:="TEXT VALUE ASSIGNMENT"
EXPLANATION: Change the value of the text variable. Note that
only the characters may be changed, but not the length.
EXPLANATION: SIMDDT output will be written on file DEBFIL.LPT.
Output in connection with a breakpoint stop will also appear on the
EXPLANATION: Output the source program lines 1 to 10.
EXPLANATION: Output the next 5 lines of the program.
EXPLANATION: Output the next 10 lines (== DISPLAY .,10).
2.4 SIMDDT input and output
The user TTY is normally used for input to SIMDDT . A "*" on the
terminal signals that SIMDDT is expecting a user command. The @
command will cause SIMDDT to read its input from the indicated
The user TTY is used for output from SIMDDT when it is in debug
mode and no USE command has been given.
Both the user TTY and the SYSOUT file are used for output from
SIMDDT when it is in error mode.The output from the ALL command is
only written to SYSOUT but all other output is written on both
If an output file is specified with the USE command it replaces the
[END OF SIMDDT.HLP]