Blaze/ATGames Ultimate Megadrive Handheld... GOAC Cart mod

Ask anything your want about Megadrive/Genesis programming.

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Munkyears
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Blaze/ATGames Ultimate Megadrive Handheld... GOAC Cart mod

Post by Munkyears » Sun Aug 12, 2012 5:24 pm

Hey, Obtained a slightly broken AT Games, handheld... With the 20 built in generic list of a few gems, with the added extra of an SD card slot...

Thinking this is exactly the same as everything other handheld, I assume its the same pinout to add the cartridge slot... also, would it not be cheaper to recreate 68000 PU rather than an entirely cheaper and more offcut emulation core which the sound and lack of VDP remove the support.. Plus i miss carrying around my nomad.. That sadly is dying!!, LCD keeps flashing every so offten then needs turning off for a few hour...

How is everyone doing? Just lost pretty much 6 years of my life's data from mega hard drive corruption,

Looking for a project to keep me occupied till i can stomach whats just happened....

Anyway thanks!
To be this good takes ages, To be this good takes Stef, Kanedafr, ChillyWilly & everyone who has helped me discover what hardwork is!

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slobu
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Post by slobu » Mon Aug 13, 2012 7:15 pm

Isn't the AT Games stuff emulation on a 32 bit chip of some sort? "Firecore" or whatever?

cdoty
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Post by cdoty » Sat Aug 18, 2012 7:46 am

slobu wrote:Isn't the AT Games stuff emulation on a 32 bit chip of some sort? "Firecore" or whatever?
I'm not sure if it's an emulator or a genesis on a chip. But, It appears to be similar in concept to the VT 03 NES system on a chip. It supports the normal VDP registers and seems to offer additional modes.

I downloaded the roms from the AtGames site (http://www.mugaatgames.net/Free_Trial.html) and they load up and output music in Fusion and MESS. They show a flash, but then it's a blank screen.

I want to look through the VDP register settings, and see if they're using some illegal bit combinations to allow for an 8 bit graphics pattern, and a larger palette. Sparkling Truffle has too many colors for a normal Genesis display.

Chilly Willy
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Post by Chilly Willy » Sat Aug 18, 2012 6:05 pm

Those are emulator clones, not GOAC. I did a quick disassembly of one those games... it looks like it assumes things like the rom being writable - look at this

Code: Select all

lbW000378	dw	$D94B
00037A	dw	$A852

00037C	MOVE.L	(lbW000378,PC),D0
000380	TST.L	D0
000382	BNE.W	lbC000396
000386	MOVEQ	#$10,D1
000388	LSL.L	D1,D0
00038A	OR.L	($FF8944),D0
000390	MOVE.L	D0,($378)
lbC000396	PUSH	#$BB40E62D
00039C	PUSH	(lbW000378,PC)
0003A0	BSR.W	lbC0003E2
0003A4	ADDQ.W	#8,SP
0003A6	ADDQ.L	#1,D0
0003A8	MOVE.L	D0,($378)
0003AE	LSR.L	#8,D0
0003B0	ANDI.L	#$FFFFFF,D0
0003B6	RTS
The code at 3E2 is a 32bx32b signed multiply. See how it assumes $378 is writable? Who knows what else they assume about the emulation.

Also, for these roms to even start on a TMSS Genesis, you'd need to put 'SEGA' at offset $100. It DOES use the standard startup, including setting the TMSS register to 'SEGA'.

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