Battery backup RAM - Page 1

Hi,

My Xevious transcode is - by necessity - not doing things "the Neo Geo way". I can't thread the title, attract (demo), coin-up and game modes into the Neo Geo BIOS without completing breaking the core for other systems.

What I've done in the past, and again for Xevious, is basically jump into the program via the Neo Geo demo hook. So it effectively takes over the Neo Geo from there and never relinquishes control. I can still detect coin-up/start etc but it's fair to say that it won't play nice in multi-slot systems. But I'm not concerned with that - I'm not expecting Xevious to be installed in any multi-slot cabs for example!

What I would like to do though is support high score saving to battery-backed RAM in the absence of a memory card. As I understand it, games define backup memory in the cart header and it is loaded/saved automatically when the BIOS calls/returns from game mode respectively. Obviously that never happens in Xevious...

So I'm thinking I can just do it myself within Xevious whenever it is required, just as I am for the memory card. However, I do want to "play nice" and have the process compatible with other games, and not trounce areas that I shouldn't be. I can't find any information on how this should be done, or whether there's any internal BIOS calls that I can make to do this? If it comes down to it, I could RE that area of the BIOS, but I'm hoping someone out there may have done something similar, or at least has some information that would help me in this regard? TIA

Regards,

To answer my own question... I actually found a disassembly of sp-s2 on my hdd that elbarto had done - not sure when, but the file date on my machine is 2013.

I've located the routines that load/save game backup data to/from BRAM but I need to do more reading to work out how the block is allocated to a game when it is first saved. Either way it looks like I can hook in and it won't require lot of code to do so...

Further to my question, for future refence to others...

The solution is trivial.

The BIOS loads from BRAM even before any cartridge code is executed. So by simply setting the correct buffer address & size in the cartridge header, I have my loading done for me. Because I take over the machine in demo mode, the BIOS never loads it again.

For saving, all you need to do is fill the buffer and call $C12322. It reads the address & size from the header, and writes to the appropriate location in BRAM.

I'm supporting both BRAM and memory card load/save. I'm using the same buffer, and the BRAM data format is identical to the memory card data format. So I can use the memory card header information (game name) to determine if valid save data was read from BRAM before patching the high score table. I just need to work out a priority scheme for BRAM vs memory card... I guess memory card should take precedence if it's inserted (for reading)? And maybe I'll always attempt to write to both...

I guess I need to skip BRAM on the AES and skip memory card on the NGCD...

EDIT: don't rush off and implement this just yet... I've discovered it corrupts my title screen after the call...

EDIT: false alarm, the bug has nothing to do with the BRAM routine...

Many thanks for your information about bioscall $C12322!

tcdev (./3):...
I guess I need to skip BRAM on the AES and skip memory card on the NGCD...

The NGCD has a built-in memory card (no BRAM!) which is accessed in the same way as on the MVS/AES, you can use the same memorycard-code for all three machines.

The NGCD has a built-in memory card (no BRAM!) which is accessed in the same way as on the MVS/AES, you can use the same memorycard-code for all three machines.

Ah thanks. I'll have a closer look before the first beta release!

tcdev (./5) :

The NGCD has a built-in memory card (no BRAM!) which is accessed in the same way as on the MVS/AES, you can use the same memorycard-code for all three machines.

Ah thanks. I'll have a closer look before the first beta release!

I've updated the high score load/save; MVS uses BRAM, all platforms use memory card routines. On MVS memory card takes precedence over BRAM, but it saves to both.