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The Memotech MTX Series |
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CP/M DDT
The Dynamic Debugging Tool
You can find the complete DDT manual on my
CP/M Documents page
Courtesy of
Oscar Vermeulen, here is a list of DDT
sub-commands :-
CP/M Commands. Excerpt from David E.
Cortesi – Inside CP/M © 1982
DDT – Dynamic Debugging Tool
DDT is used to debug programs written in
assembly language. It also finds use as a special utility
program for building program images, and in applying patches to
fix programs.
See the USER command for an example of using DDT to load the
image of a command. An assembly-language program can be built
from different modules, each assembled at a different, known
origin. For example, a main program might contain a reserved
space for a terminal driver subroutine. Different terminal
drivers can be prepared, each customized for a particular
terminal type. The correct driver can then be incorporated in
the main program with DDT:
ddt main.com load image of main program
-iterm120.hex prepare to load driver for Soroq IQ120
-r read terminal driver to its origin
-g0 warm start, leaving merged program
save 37 main120.com save customized command program
DDT{ fileref }
The DDT command initializes a debugging session. The code of
the debugger is loaded and moved to the top of the Transient
Program Area. replacing the CCP. The address of the end of the
Transient Program Area in low storage is changed to protect the
debugger.
If fileref is specified, that file is loaded
into the Transient Program Area. The reference must be explicit
and have a filetype of either .HEX or .COM. A .COM file is
loaded at 0100h: a .HEX file is loaded at its assembled origin.
The debugger then prompts with a hyphen and waits for a
subcommand. A table of DDT subcommands follows this topic.
The command is ended by a warm start. One may be obtained
either by typing control-c or by entering the G0 (go to zero,
i.e., to the warm start jump) subcommand.
Summary of DDT Subcommands
| Syntax |
Description |
| A start |
Assemble into storage: DDT prompts
with successive addresses from start. Enter
operation names, and register names or hex values as
operands. End the process with a null entry. |
| D {start} {, end} |
Display storage: DDT displays
storage in hex and ASCII, 16 bytes per line. The
display begins with start if given, or where the
prior D left off, or with the HL value of the last
instruction traced. It ends with end if given, or
after 12 lines. Use any key to end the display
early. |
| F start, end, xx |
Fill storage: DDT replicates xx in
every byte from start through end. Caution: DDT will
happily fill right over itself and the BDOS if told
to do so. |
| G {start}{,b1{,b2}} |
Execute program: DDT transfers
control to start if given, or to the test program's
PC. If one or two break addresses are given, DDT
makes each an RST 7 instruction: control returns to
DDT if the program reaches one and the instructions
are restored. |
| H first, second |
Hex arithmetic: DDT responds with
two numbers, first ^ second and first-second. |
| I fileref |
Initialize FCB: fileref is set in
the default FCB at 5Ch. Any drivecode is ignored.
The FCB may be used by the test program: more often
it is used by the R subcommand. Use S to set up a
drive number. |
| L {start}{,end} |
List instructions: DDT displays
storage as instructions in assembler format, from
start if given, or where the last L left off, or
from the PC address of the last traced instruction.
The display ends with end if given, or after 11
lines have been typed. Use the delete key to stop
the display. |
| M start, end, to |
Copy storage: DDT copies the block
of storage from start through end to the address to. |
| R {bias} |
Read program: The file named in the
default FCB at 5Ch is loaded as a program. The
filetype must be .COM (load address is OlOOh+^f'a.?)
or must have the .HEX format. In that case the bias
is added to the load address in each line, causing
the file to load away from its assembled origin. The
highest load address this session and the current PC
value are displayed. |
| S start |
Modify storage: DDT prompts with the
address start and that byte's contents in hex. Enter
a new value, or CR alone, to leave it unchanged. DDT
prompts with the next address; enterperiod, CR to
end. |
| T {count} |
Trace program: An instruction is
traced. The test program PC provides its address;
use X to set it. The register state and the
instruction are shown before the instruction is
done; use X to see the instruction's effect. If
count is given, DDT continues for that many
instructions; use the delete key to stop it early. |
| U {count} |
Trace without display: Instructions
are traced as for T but no state display is typed.
|
| X |
Display program state: The test
program registers and the instruction addressed by
its PC are shown. |
| X register |
Modify register: DDT prompts with
the contents of the named register or flag. Enter CR
alone to leave them unchanged, or enter a new value.
The registers are A, B, D, H, S (for SP), and P (for
PC). Flags are C, Z, M, E, and I. |
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