Search found 283 matches

by Charles MacDonald
Mon Jul 31, 2017 2:06 am
Forum: Blabla
Topic: Alien Soldier graphic glitch
Replies: 2
Views: 243

Alien Soldier graphic glitch

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...
by Charles MacDonald
Mon Jan 02, 2017 2:42 am
Forum: Video Display Processor
Topic: Mode 4 VRAM Timing
Replies: 4
Views: 676

Re: Mode 4 VRAM Timing

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...
by Charles MacDonald
Thu Aug 18, 2016 8:27 pm
Forum: Megadrive/Genesis
Topic: Questions on developing a Mega Drive emulator
Replies: 39
Views: 3798

Re: Questions on developing a Mega Drive emulator

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...
by Charles MacDonald
Thu Aug 18, 2016 4:21 pm
Forum: Megadrive/Genesis
Topic: Questions on developing a Mega Drive emulator
Replies: 39
Views: 3798

Re: Questions on developing a Mega Drive emulator

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...
by Charles MacDonald
Mon Jun 27, 2016 3:08 am
Forum: Megadrive/Genesis
Topic: Z80 and DMA
Replies: 1
Views: 680

Z80 and DMA

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...
by Charles MacDonald
Tue Jun 14, 2016 3:14 am
Forum: Megadrive/Genesis
Topic: A few questions :)
Replies: 15
Views: 2749

Re: A few questions :)

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...
by Charles MacDonald
Tue Jun 14, 2016 3:10 am
Forum: Hardware
Topic: GBS-8220 fuzzy and green
Replies: 7
Views: 1285

Re: GBS-8220 fuzzy and green

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...
by Charles MacDonald
Sun Apr 24, 2016 10:34 pm
Forum: Megadrive/Genesis
Topic: Alright dudes, I need your help! (soft-reset bug)
Replies: 37
Views: 3478

Re: Alright dudes, I need your help! (soft-reset bug)

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...
by Charles MacDonald
Sat Mar 12, 2016 8:59 pm
Forum: Demos
Topic: Virtua Worm for SEGA Genesis
Replies: 3
Views: 1139

Re: Virtua Worm for SEGA Genesis

Wow, very nice! Also impressed to hear music and some SFX too.
Given the limitations of the Genesis, the title screen came out well. :D
by Charles MacDonald
Sun Feb 14, 2016 1:05 am
Forum: Cartridge
Topic: SRAM write protect
Replies: 5
Views: 1436

Re: SRAM write protect

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...
by Charles MacDonald
Sat Feb 13, 2016 8:35 pm
Forum: Blabla
Topic: The calendar. Birthdays members of the forum.
Replies: 3
Views: 1015

Re: The calendar. Birthdays members of the forum.

Happy birthday! Thanks for all your contributions to this forum. :)
by Charles MacDonald
Fri Jan 15, 2016 6:30 pm
Forum: Cartridge
Topic: SRAM write protect
Replies: 5
Views: 1436

Re: SRAM write protect

It's in the 32X documentation that's floating around. Also I noticed Beyond Oasis (and perhaps others?) write to these Sega-defined mapper registers despite not actually having one (I checked a real cart), presumably as the development hardware had it. Since the functionality isn't present in the ca...
by Charles MacDonald
Fri Jan 08, 2016 12:19 am
Forum: Cartridge
Topic: Add feature to a cart
Replies: 10
Views: 2100

Re: Add feature to a cart

- how is it possible to generate DTACK ? I understood it means address is available on the address bus but who defined it (when it's ready) ? You assert DTACK when you detect the address range you want is being accessed, meaning /AS is low and the address lines match the address range you want. For...
by Charles MacDonald
Thu Dec 24, 2015 4:59 pm
Forum: Cartridge
Topic: Add feature to a cart
Replies: 10
Views: 2100

Re: Add feature to a cart

Sometimes you see communication methods where there is no handshaking (acknowledgement or status indicators) and I don't know how they are supposed to work reliably. :) I realized since the circuit has a 74HCT74 there's a 2nd flip-flop we can use, so I expanded the schematic a little. Now when you w...
by Charles MacDonald
Thu Dec 24, 2015 6:33 am
Forum: Cartridge
Topic: Add feature to a cart
Replies: 10
Views: 2100

Re: Add feature to a cart

So, if I want to add an AVR on a cart and to control, from it, several others modules (ex: bluetooth for faster serial transfert) how could I power it ? It's OK to just use the +5V from the cartridge port directly, it seems unlikely what you are adding will use more current than is available. Other...