SpritesMind.Net

You can still store graphics data in $800000-$9FFFFF if you'd like, you just can't transfer it to the VDP using DMA. Instead you can write 68000 code to transfer the data to the VDP.

If you test it let us know how it works. I think nobody's tried it before, so your results will be interesting.

The ROM3-CE# signal is correct though IC5B doesn't need input A=A23, as A23 is already checked by IC5A, thus when IC5B is decoding A23 is always low. DTACK# can be the same as your ROM3-CE#, but you can run it through a 74HC1G125 buffer like this to make it open drain: Input A : Ground Output enable...

TMSS isn't too bad to deal with, it just takes a little more complexity on your end: 1. Your ROM should contain the ASCII text "SEGA" at offset 0x100. (e.g. the CPLD outputs that hardcoded data when reading that memory range) 2. If your diagnostic software needs to write to the VDP, it has to satisf...

I had a similar kind of experience on a past project and it was helpful to reduce the complexity and just try a simple test case: ignore the SDRAM entirely and output fixed ROM data to run a small program that is only a few words long so it can fit within the CPLD. For example something like: dc.l 0...

Unfortunately it doesn't speed anything up, the access time during V-Blank is the same as when the screen is turned off. However you can get more time to do DMA transfers by "letterboxing" the display, where you turn off V-Blank early (say line 200) and then back on late (say line 8 of the next fram...

I've seen an issue on some flashcarts and my own dev hardware where there are graphical glitches in this game, during the 7 Force battle when you fight the cat robot thing. It's happened with several different Genesis consoles. Here's how it should look: https://youtu.be/AaSsBtFD4Xc?t=182 Now what I...

Wow, great job! Nice to have a very technical post to start the new year. :) About the sprite Y read parts, any idea why it goes up to 15 and not 7 given that there's eight possible sprites per scanline? Or is this a side effect of having to read data in some wider width? (say 16 bits at at time, so...

Mask of Destiny, good catch! I've edited my post for clarity. unlicensed EA games (Budokan, etc.) use H40 mode with the wrong combination of RS1,RS0 set, How does that even work, that should result in an invalid TV signal. For one of the combinations of bits yep, it's a scrambled mess, for the other...

Bart did a good write-up on some poorly documented/undocumented aspects of the 68000 too: https://emu-docs.org/CPU%2068k/68knotes.txt Other quirks include: MOVEM reading one address past the source location: http://gendev.spritesmind.net/forum/viewtopic.php?f=13&t=2010&p=25882 CLR to memory being re...

When doing DMA from the 68K address space to VRAM, what happens when the Z80 tries to read banked RAM memory during a long transfer? I'd assume the Z80 is halted until DMA is over, but I think this would affect sample playback. Is there a priority system where the Z80 can always complete an access f...

The Game Genie disables all the user-accessible registers when it is running a game. The only thing you could do is checksum the ROM and verify if it is bad or not, which would indicate the Genie was patching one or more locations. I can't remember if the Genie software fully clears out RAM and VRAM...

I'd try gently pressing on around the edges of each of the surface mount chips to see if anything changes. That would indicate a bad solder joint where a pin isn't contacting the pad on the PCB well. Or press gently on the PCB to flex it a bit and see if there's any changes. I know the cables and Ge...

If the Z80 is held in the reset state (by $A12000) then busreq will never be asserted and the loop will never exit. This is because the Z80 reset logic has a higher priority than the bus request logic. Maybe check for any unintended writes to $A12000 in the sound/joypad routines and verify the Z80 i...

Wow, very nice! Also impressed to hear music and some SFX too.
Given the limitations of the Genesis, the title screen came out well.

I opened a few carts today. I can confirm that at least Phantasy Star IV and Sonic 3 do not implement the write protect bit in either game. I wonder which other games would be candidates to look at? Off topic: My Super Street Fighter II cartridge had a modification compared to db-elec's, there's a 0...