September 10th, 2009
Don’t you just hate it when you encounter a very strange bug that can’t be logically explained, you take lots of hours to trace/debug it and you end up finding out that the cause was at most one single line of code? That was the case here.
Some games would fail to “identify” the connected Visual Memory Unit (that’s the Dreamcast equivalent of a memory card with integrated LCD screen and clock). As a result they would not use any of the VMU features, they would still complain that there is no VMU connected and of course they would not be able to save/load game data.
So I took the time to debug the issue… and it turned out that the error was caused by something relatively minor. Wonder if all the games that had similar issues are fixed now. We’ll see I guess.
For the time being here is a pic of the game “Spawn: In the Demon’s Hand” after the bug was squashed.
Tags: card, dc, dreamcast, emulator, fix, memory, nullDC, vms, vmu
Posted in nullDC | 12 Comments »
September 6th, 2009
So there I was the other day taking a look at some of the issues on nullDC (ehm, you know, that Dreamcast emulator).
Of all the known issues the game D2 had one of the strangest ones. The game prompts you to swap discs at predetermined occasions but it fails to detect that the disc swap actually happens.
So I fire up the debugger, start the game and begin stepping/skipping instructions. Nothing comes up so I proceed to step 2, disassembling. After running through the disassembled code for some hours and marking/tracing relevant code I fire up the debugger again and start manipulating the game code… and voila:
Right, now we got the game to “detect” that we inserted the same disc… not really, but at least there is some sort of reaction.
What could be the “right” way to do this? Running through the disassembled code a bit more and taking a look at some documentation is enough to point out the most possible cause. Add to that drkIIRaziel’s code which is full of info messages and there you have the cause and the solution. Adding a quick ugly hack in the GD-ROM code proves that, the problem is solved and the game swaps fine. One problem gone, a billion remaining.
The end result is drk pointing out that the GD-ROM code needs another re-write… yeah, right, maybe next year or something.
Tags: D2, dc, dreamcast, emulator, fix, nullDC
Posted in nullDC | 1 Comment »