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DDT v43(627) - Warnings and Hints
This version of DDT contains all development work currently
planned. Following is a list of hints, aspects, and
hitherto undocumented features, and a brief discussion of
useful information in DDT's Program Data Vector.
1. DDT v43 is not officially supported on TOPS-20 5.1
or 4.1 systems. However, user DDTs may be used on
a 5.1 system which has installed the following
Autopatch tape #8 includes edit 3122 to TOPS-20
which modifies the PDVOP% JSYS. This edit changes
the monitor's interpretation of the .PVNAM word of
the Program Data Vector, to agree with LINK and
DDT. In order to use DDT v43 successfully on a
TOPS-20 5.1 system, you must either install tape #8
or install the following patch:
ponam+6/ TLNN T1,777777 tlne t1,400000
2. Monitor symbols from MONSYM and MACSYM can be made
available from XDDT by typing the command
which causes DDT to select its own symbol table for
use. This is equivalent to running SDDT in v42.
Note that this symbol table may be selected at any
time, even when debugging another program; the
program's symbol table may be restored with the
3. Users of VT200-series terminals will note that the
grave character (`) is equivalent to the escape in
DDT commands. This change does not affect use of
the grave in character strings.
DDT'S PROGRAM DATA VECTOR
XDDT has a Program Data Vector associated with it, named
"DDT%". This PDV has several useful pieces of information
o A symbol table vector, pointing to symbol tables
loaded from MONSYM and MACSYM.
o An "exported information" vector, containing
pointers to useful DDT internal locations.
As noted above, DDT's symbol table may be selected with the
command $$:/DDT%/. This causes symbols defined in MONSYM
and MACSYM to be available for use.
The "exported information" vector is pointed to by word
.PVEXP in the PDV. This is a counted vector with the
DDTEXP: EXP EXP.L ;LENGTH OF BLOCK
IFIW DDT ;DDT'S START ADDRESS
IFIW $0BPT ;UNSOLICITED BREAKPOINT ADDRESS
IFIW $5M ;SYMTAB LOCATION INFO
IFIW SECUDD ;SECTION OF UDDT STUB
This vector may be used, for example, to enter DDT at the
unsolicited breakpoint. Assuming that your program and DDT
are both in non-zero sections, and that T1 contains the
address of DDT's PDV, the following code sequence could be
XMOVEI T2,@.PVEXP(T1) ;GET ADDRESS OF EXPORT VECTOR
JSR @2(T2) ;ENTER AT UNSOLICITED BREAKPOINT
DDT's exported information vector is reserved to Digital.
Customers wishing to make use of DDT's PDV for other
purposes should use word .PVCST of the PDV.