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Paulko64
Registered: Jul 2010
Posts: 24 |
Reverse debugging in emulator?
Hi all,
I'm currently working on a game-project that has high irregular CPU load during each frame. I've coded everything in such a way that all this irregular code is ran during a mainloop and starting of the routines is regulated during raster-irqs (besides the multiplexor and music calls).
Now this all works perfectly except for once in a few minutes my game crashes (CPU-jam), because it apparently jumped to a strange adres (ZP in my case). I'm not sure what happened but maybe I didn't end the irqs well enough, or perhaps I used the same ZP-adres for indirect adressing in both main and irq-code, which then screws up code if an irq fires at exactly the right (wrong!) moment...
Anyhow, this proves to be very hard to troubleshoot. So I thought, isn't there an emulater that supports some kind of "reverse debugging"? I.e. when I get a CPU-jam can I trace back what instructions were used just before? Or maybe an emulator that supports writing all instructions executed to a textfile which I can then trace back? Although this last option will probably generate a HUGE trace-file.
Does anybody know how to accomplish something like this?
Thanks,
PaulKo64 |
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MagerValp
Registered: Dec 2001
Posts: 1078 |
Quote: Hmms.. configure && make worked quite nicely for me on Mac OS Mountain Lion. Although I have all the dev tools installed from xcode etc... perhaps that was your issue?
This was on 10.7.3 with Xcode 4.2 (with command line tools installed). Specifically it failed compiling the library dependencies but I don't remember which one.
I should try in a fresh VM with 10.8.1 and Xcode 4.4 and see what happens... |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: This was on 10.7.3 with Xcode 4.2 (with command line tools installed). Specifically it failed compiling the library dependencies but I don't remember which one.
I should try in a fresh VM with 10.8.1 and Xcode 4.4 and see what happens...
OSX v10.8.1 with xcode 4.4.1 here. |
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Paulko64
Registered: Jul 2010
Posts: 24 |
Martin: Thanks for your "Tweaked" VICE! The "chis" command works beautifully! However, my next question is how to scroll upwards in the VICE-monitor, or how to save the history to a file? At the moment I can't see the point where it exactly went wrong :-( |
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Endurion
Registered: Mar 2007
Posts: 73 |
You could try with the remote monitor, this way you can get all the output. |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
you can't scroll backwards in the windows gui? wow =) |
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Norrland
Registered: Aug 2011
Posts: 14 |
Quote: you can't scroll backwards in the windows gui? wow =)
No :P I had the same kind of problem while debugging some stuff just earlier today..
Therefore, this remote monitor sounds interesting. I've searched the vice manual and the web but haven't managed to get it up and running. I've tried "-remotemonitor" on the commandline but is obviously missing something.. I would appreciate if someone could point me in the right direction. |
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Perplex
Registered: Feb 2009
Posts: 255 |
Quoting H MacaroniI've tried "-remotemonitor" on the commandline but is obviously missing something.. I would appreciate if someone could point me in the right direction.
To connect to the remote monitor from a separate terminal on the same machine, use "telnet localhost 6510". You can of course also connect from a different computer, provided there's no firewall blocking the port.
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Martin Piper
Registered: Nov 2007
Posts: 722 |
The version of VICE you have (from me) doesn't have the telnet feature enabled, the source is too old. But the CPU history of instructions is limited to the last 64 instructions.
If you can I would recommend trying to spot a pattern where the crash comes from in the CPU history and setting a breakpoint earlier until you start tyo discover where the wrong code is coming from.
Or if you suspect wrong memory is being accessed then use watch with a memory range.
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Martin Piper
Registered: Nov 2007
Posts: 722 |
OK, because I'm a nice chap I expanded the CPU history to be 256 instructions and also added the "telnet localhost 6510" debug log stuff.
You can get it from:
http://www.wellytop.com/VICEtweaked2.zip
You won't be able to type commands into the telnet window so you still need to use the monitor window.
Also you'll need to open the monitor window before trying to connect ot localhost port 6510.
Sources: https://github.com/martinpiper/VICE/
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Paulko64
Registered: Jul 2010
Posts: 24 |
Yeah, finally solved the bug! I couldn't have done it without the "chis" command.
What happened was that due to a negative offset an unrelated routine corrupted the hi-byte in one of my jump-tables. Now minutes later when actually using this particular jump-adres I ended up in zero-page where after some random instructions it encounterd a BRK instruction and crashed soon thereafter!
So luckily I can now continue with the rest of the game.
Thanks all!
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