[galaga] help with finding memory address of score

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anderson110
Posts: 3
Joined: Mon May 17, 2021 5:13 am

[galaga] help with finding memory address of score

Post by anderson110 »

I'm trying to figure out the memory address that holds the score in MAME galaga.

I've been able to use the cheat debugger to find that the number of shots are stored at 9846, and the number of hits are stored at 9844, but I have had no luck turning up the location of the actual score.

I've been looking in the range 8800-9fff, since according to this page (http://tech.quarterarcade.com/tech/MAME ... spx?g=1042), this is the range that is used as "RAM". But I could easily be missing something or looking in the wrong place.

Any help appreciated.
anderson110
Posts: 3
Joined: Mon May 17, 2021 5:13 am

Re: [galaga] help with finding memory address of score

Post by anderson110 »

I thought it might be a useful strategy to figure out the video RAM address where the score is written, and then use a watchpoint to try to reverse engineer the code when that video RAM gets written, but I haven't been successful in finding that either. I can find most locations on the screen around 8100, but the area near the top of the screen doesn't seem to be contiguous with the memory mapping of the rest of the screen. So I got stuck going that route as well.
anderson110
Posts: 3
Joined: Mon May 17, 2021 5:13 am

Re: [galaga] help with finding memory address of score

Post by anderson110 »

I think I may have figured out one way to get at this. The screen RAM addresses for the score digits are at:

0x83F8 for the 1's place
0x83F9 for the 10's place
and so on.

Values of 0-9 map to themselves, and 24 is the code for a blank.

I'm not sure if the value is stored somewhere else as well, or if it's just updated on the fly in the video RAM.
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