Patch to Solve conflicts between Snk games and 4Mb

[shinhoshi]

As you probably know, gamess like Kof 96, Kof 97, Metal Slug, Samurai Shodown 4 or Real Bout Garou Densetsu Special have problems when used with the official SEGA cart (4MB cart). They only seem to work properly with the 1Mb cart from SNK.

Could a patch be made in order to solve these problems ?¿??

 

[Butane Bob]

The only snk game that acts like that is King of Fighters 95, and that's because the cart that comes with it is a ROM cart not a RAM cart.

 

[shinhoshi]

If you are using the 4MB cart (the official one from CAPCOM-SEGA), I can assure you that the games don't work properly. A lot of frames are lost and instead of them you can see black quads on screen. Something very ugly.

 

[Tagrineth]

Originally posted by shinhoshi@Jun 17, 2003 @ 07:38 PM

As you probably know, gamess like Kof 96, Kof 97, Metal Slug, Samurai Shodown 4 or Real Bout Garou Densetsu Special have problems when used with the official SEGA cart (4MB cart). They only seem to work properly with the 1Mb cart from SNK.

Could a patch be made in order to solve these problems ?¿??

You'd have to reprogram the games.

SNK's 1MB and Capcom/Sega's 4MB expansions are wired differently.

 

[mal]

So how does an AR4M+ cope with both?

 

[Shakey Jake33]

Originally posted by mal@Jul 1, 2003 @ 10:32 AM

So how does an AR4M+ cope with both?

I seem to remember the cart itself auto-switches, as in cuts some circuits and opens some others.... the actual hardware itself changing.

 

[mal]

But how does it 'know' if it should be 1MB or 4MB?

 

[Jaded God]

Originally posted by mal@Jul 1, 2003 @ 02:47 AM

But how does it 'know' if it should be 1MB or 4MB?

that's a good question Mal, :agree

 

[ExCyber]

The only documentation I have on the RAM expansion carts suggests that Sega specced both the 1MB and 4MB carts, and I've seen no indication that the AR4M Plus can actually "auto-switch" anything; the carts are very similar but not identical. AFAICT from the docs, the only way for the AR4M Plus to "know" would be to hash the game header, check the title / product number, or something similar

 

[Tagrineth]

Well, think that the 1MB expansion is more or less solely used by SNK. Could be a quick vendor ID check or something...

 

[SegaSaturnDDR]

ahem, also i know that kof 97, Real bout special, and metal slug DO work with an official cart, but those others refuse to recognize the cart, and the graphics get reaaaaaal strange.

 

[antime]

Just a suggestion, but maybe the SNK cart behaves differently from Sega's when accessing outside the designated area. Inspection of the code would reveal if SNK's games are using the cartridge in some odd way. (There might also be a difference in how the game sets up the CS0 RAM refresh - if it is set to a lower value than specced by Sega the official carts may simply be losing the loaded contents. Wait states is another possible culprit.)

 

[ExCyber]

Another possibility is that the SNK games access 4MB carts differently from 1MB carts (based on the 5C vs. 5A ID byte), and the bugs are in the game code. I seem to remember several people with the older AR4M Plus hardware (which always identifies as a 1MB cart) saying that they had no problems with SNK games...

 

[SegaSaturnDDR]

it sounds likely, since usualy games that need ram wont boot if they dont find it.

 

[M3d10n]

I got a weird cart, that works as both 1MB and 4MB cart, and has a switch.

The switch has 3 settings (?). The left one is 1MB, the right one is 4MB, the middle one... I dunno. But 4MB games boot fine with the middle setting.

This cart has some weird behaviors... SNK games rarely boot with the 1MB setting. I need to set the cart into 4MB, or the middle setting, to get them to work. But if I leave the cart like that, I might get those errors (some characters get corrupted as player 2). Things go back to normal if I set the cart to 1MB while the game is running.

 

[Tagrineth]

Originally posted by ExCyber@Jul 1, 2003 @ 10:01 AM

Another possibility is that the SNK games access 4MB carts differently from 1MB carts (based on the 5C vs. 5A ID byte), and the bugs are in the game code. I seem to remember several people with the older AR4M Plus hardware (which always identifies as a 1MB cart) saying that they had no problems with SNK games...

The wiring is different.

The AR4M+ has a 4MB RAM with appropriate connections for both the SNK 1MB and Capcom/Sega 4MB add-ons... so it can work with both. I'm sure the games themselves have some kind of flag by which the 4M+ can tell if it'll need 1MB or 4MB.

 

[antime]

The wiring is different how? Saying the wiring is different implies to me that the memory map is different, but the Action Replay at least has RAM from 0x22400000 to 0x227FFFFF, just like specced by Sega. Accesses outside that area do not touch the memory but the games still work.

 

[Tagrineth]

Originally posted by antime@Jul 1, 2003 @ 10:49 PM

The wiring is different how? Saying the wiring is different implies to me that the memory map is different, but the Action Replay at least has RAM from 0x22400000 to 0x227FFFFF, just like specced by Sega. Accesses outside that area do not touch the memory but the games still work.

The connections between the RAM chip, the circuit board, and the cartridge logic.

 

[ExCyber]

The connections between the RAM chip, the circuit board, and the cartridge logic.

As far as I can remember, on my Action Replay 4M Plus, the address bus on the cart slot is just connected to the DRAM through a pair of muxes. This would not provide the same memory map as what would be on the 1MB cart specced by Sega - if a game just used the 1MB RAM where it was officially mapped it should work fine since they overlap, but any access outside the RAM area for 1MB can't be guaranteed to be compatible (it probably mirrors on a real cart, while it would just read/write normally on a 4MB one).

 

[WiseMan]

does the AR4+ have the 1mb & 4mb ram types separate from each other within the cart or does it just use 4mb that is accessible through both methods?