home PDP-10 TOPS-20 Commands Reference Manual Top: Chapter 2 Command description

DDT

Loads or merges a debugging program into memory (unless one is already there), then starts it.

Format

@DDT/switch(es)

where:

Characteristics

If a Debugging Program is Already Loaded

If you have already loaded a debugging program into memory along with your program, the DDT command starts the debugging program.

If Your Program, But Not a Debugging Program, is Already Loaded

If a program containing symbols is in memory without a debugging program, the DDT command merges SYS:XDDT.EXE into memory, then starts this debugging program. However, if some of XDDT's pages include some of the same pages as the existing program in memory, then the DDT program is not placed into memory, and you receive the error message, "?Illegal to overlay existing pages." To force the pages to be overlaid, reissue the DDT command using the /OVERLAY switch.

If There is No Current Program

If you do not have a program in memory, or if no program in memory is in the current fork, or if your program does not contain symbols, the DDT command puts SYS:XDDT.EXE into memory and starts it.

Compatibility with Previous DDT Versions

The UDDT program run by the DDT command has been replaced by the XDDT program. For compatibility with programs that reference UDDT, a stub program named UDDT references the XDDT program.

Hints

Using DDT to Create a Program

You can use DDT to begin typing instructions directly into memory, without first putting the instructions into a file for later compilation and loading. Give a RESET . (period) command to clear the current fork, then the DDT command. This will load the SYS:XDDT.EXE program. Then you can give commands within XDDT to create your own program. When using the XDDT program, you can use all the symbols in the system parameter file MONSYM.MAC.

See the TOPS-20 Monitor Calls Reference Manual for more information about MONSYM.MAC. This method of writing a program is most useful for testing special cases, or for learning to use TOPS-20 monitor calls.

Special Cases

Using COBDDT

If you put COBDDT into memory along with a COBOL program, the DDT command starts the UDDT program, not COBDDT. Use the REENTER command to start COBDDT in this case.

Effect on Memory and Terminal

The DDT command merges the SYS:UDDT.EXE program into the current fork and starts it, or loads and starts SYS:XDDT.EXE. If you have already loaded a debugging program, the DDT command starts this program.

Related Commands

Examples

1. Give the DDT command to begin debugging a program in the current fork in memory.

   @DDT DDT
   

2. Give the DEBUG command to debug a FORTRAN program; type a CTRL/C to return to TOPS-20 command level so you can find out the current load averages and number of jobs for the system. Return to your debugging program (FORDDT in this case) by giving the DDT command.

   @DEBUG TESTF1
   LINK:   Loading
   [LNKDEB FORDDT Execution]
   
   STARTING FORTRAN DDT
   
   >> ^C
   @SYSTAT SYSTEM
    Fri 20-Apr-79 13:50:01  Up 36:47:55
    35+14 Jobs   Load av (class 0)   0.72   0.81   1.33
   
   @DDT
   
   STARTING FORTRAN DDT
   
   >> START
   
   THIS IS A TEST.
   
   END OF EXECUTION
   CPU TIME: 0.04  ELAPSED TIME: 0.33
   EXIT
   @INFORMATION MEMORY-USAGE
   
    66. pages, Entry vector loc 0 len 254000
   0-12     Private   R, W, E
   400      Private   R, W, E
   401-466  <SUBSYS>FOROTS.EXE.3  3-70   R, CW, E
   

3. Display the programs in memory with the INFORMATION FORK-STATUS command. Then use the FORK command to make the CLIP program the new current fork. Verify this with INFORMATION FORK-STATUS and then merge the UDDT program with the CLIP program.

   @INFORMATION FORK-STATUS
       EMACS (1): Kept, HALT at 50340, 0:00:03.6
       CLIP (2): Kept, HALT at 70363, 0:00:00.2
    => UNITS (3): HALT at 162, 0:00:00.9
   @FORK CLIP
   @INFORMATION FORK-STATUS
       EMACS (1): Kept, HALT at 50340, 0:00:03.6
   =>  CLIP (2): Kept, HALT at 70363, 0:00:00.2
       UNITS (3): HALT at 162, 0:00:00.9
   @DDT
   DDT