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DDT command

The DDT command loads  or  merges  a  debugging  program  into  memory
(unless one is already there), then starts it.




     /switch   is one or more of the following:

                    /OVERLAY       allows pages of the DDT program  to
                                   be  loaded  over  pages occupied by
                                   the existing program in memory

                                   specifies the memory section  (from
                                   0  to  37  octal)  into  which  the
                                   debugging program is to be  loaded,
                                   run, or merged


     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

     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          The UDDT program run by the DDT command has been replaced by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.


     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

     DEBUG                    for loading your program  along  with  a
                              particular  debugging  program  (such as
                              FORDDT or COBDDT).

     FORK                     for selecting the current fork.

                              for  displaying  the  numbers  of  pages
                              occupied by the program in memory.


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


     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]


              >> ^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



              >> START

              THIS IS A TEST.

              END OF EXECUTION
              CPU TIME: 0.04  ELAPSED TIME: 0.33

               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.

                  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
                  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