functions of debugger (log, snapshot)

[littbarski]

hello, I am not a developer but only a 90s DOS gamer :). I try to find out little things about some DOS games to perhaps mod them. So now for the first time I used the Debug option in DOSBox-X. But the code is running like hell, no chance to see anything going on when I do for example a mouse click on a certain menu in the game. I tried to reduce the CPU speed but no change.

So my questions are: is there any way to stop the Debug code view by key or mouse click ? (as said I know pretty nothing, so like interrupts may be too difficult already for me) I tried with bp int33h in the code view but I don't see the fast running code stop.

As I guess that my first question will not give me a way to solve my issue: how does the log in debug work, can I somehow export the last 20 or 50 code lines running in ther debug window into file or clipboard?

In general I don't see why the code is so fast as the game example is a 90s soccer manager without happening anything on the screen (no movement visible for me).

[joncampbell123]

If the game is using INT 16h (which is unlikely past the 1980s) you can break on that. If the game hooks the keyboard ISR (which is more likely) you can break on INT 9 (IRQ 1), unless the game is protected mode, where it might have relocated IRQ 1 (use the PIC command to see what those interrupts are and break on whatever IRQ it is).

For the mouse, it may be polling INT 33h, or it may have installed a "mouse interrupt handler", which means you will have to break on the mouse interrupt (IRQ 12) and step into the game's interrupt handler.

You can use the LOG command to run the game with each instruction logged to a file LOGCPU.TXT. LOG fff will log 4095 steps. If it's not clear, log takes the number of CPU instructions as hexadecimal digits.

[littbarski]

thank you very much. I still don't understand enough :).

• do I use the LOG command under Debug > "Show code overview" (I have German texts) ?
• where would I use IRQ 12? I tried bp int 33h in the command but not effect.
• but most important, as the log would be perhaps fine to me: my logcpu.txt is empty after creation by LOG under coder overview, and in general the game is stopping in normal debugging mode, only working in debug "Observation mode", not in the normal "start debugger" or "start normal", in those two cases the game stops and can not be restarted without closing DOSBox-X. So how can I make very fast a log of the last code lines after I clicked something in the game? (shortcut?)

[joncampbell123]

If the debugger interface is under "code overview", then yes, use the LOG command.

The LOG command is not fast, because it's writing to a file for every instruction to log it.

Use the PIC command in the debugger or "code overview" to look at the hardware interrupt vectors.

Look up the vector for IRQ 12, that's usually 0Ch but some protected mode DOS extenders redirect that. Then type "BPINT", space, then the interrupt vector in hexadecimal.

[littbarski]

hello I am still trying to get the debugger work :) . Now I found our more how it works, and get the command enter in the additional Debugger window.

In the main DOSBox-X, I have the options in the menu Run debugger / Run normal / Run watch.

But I only get a chance to enter some command when I choose Run debugger, but then the game is frozen? Is this normal like that perhaps?

When I choose Run Normal and Run watch, I can play the game (it is the On the Ball soccer manager V1) but no command entry possible. With Run Normal, no code is changed on the debug window, with Run watch, it runs like hell.

I would like to see code or write a log when I click in the menu to see why there is always a black screen (with right mouse even as long as I hold...).

[littbarski]

well, where should I usually use those debugger commands? the code overview is the only way I found. But when I put PIC into it then the game and debugger freezes.

[joncampbell123]

The PIC command prints the information in the window at the bottom. If there is more than can be shown at once, it pauses and you need to hit q to break out or ENTER to view more.

When it does this it explicitly says so at the very bottom when it is waiting for q or ENTER.