Search found 884 matches

by Eke
Tue Apr 30, 2019 8:56 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Is ff8038-ff8041 writable? (CDD status registers.) I am guessing not, and that they're for the CDD to write to them. Indeed they are not. They are written by the ASIC upon receiving CDD status words through the CDD interface (4 bits at a time). The manual says that writing ReceiveStatus[7] generate...
by Eke
Tue Apr 30, 2019 6:24 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Would that apply to the RAM as well? Seems like it would Yes, the main ASIC is handling entire sub-CPU address decoding so this apply to everything mapped in sub-CPU range (no software rely on this though) May I ask which document/page? I'm having trouble finding it. You have to look at registers d...
by Eke
Mon Apr 29, 2019 6:21 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Would that apply to the RAM as well? Seems like it would Yes, the main ASIC is handling entire sub-CPU address decoding so this apply to everything mapped in sub-CPU range (no software rely on this though) May I ask which document/page? I'm having trouble finding it. You have to look at registers d...
by Eke
Mon Apr 29, 2019 9:57 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Oh god, if i had this documentation back in time... i spent so many time (and CD) to RE the MegaCD just for this CDD stuff :D I didn't had any MegaCD back in time and it's Red5 (the guy owning GenesisProject website which was referencing Megadrive emulators compatibility list back in time) who lite...
by Eke
Sat Apr 27, 2019 10:45 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Lastly, about CDD... : $ff8037.d2, HOCK. "Setting this bit causes communication with the CDD to commence." I'm sorry that wasn't vague enough, could you be a little less specific? You have to understand that this register is not supposed to be used by game software developers for which those manuals...
by Eke
Sat Apr 27, 2019 8:48 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

Now, about CDC CDC interrupts: these appear to be an amalgamation of four interrupts. DECI = decoder, DTEI = date transfer end, CMDI = command buffer not empty, SYEIN = sync ... something. It's not documented. I don't know anything about the later or where you get that from but I doubt it exists, IF...
by Eke
Sat Apr 27, 2019 12:30 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

I've seen people say they mirror every $40 bytes and every $200 bytes. That they only map to a120xx/ff80xx or that they map to a12000-a12fff/ff8000-ffffff. Main-CPU side was verified by Charles (see http://gendev.spritesmind.net/forum/viewtopic.php?f=5&t=1276. Afaik, bus arbiter use VA23-VA8 for de...
by Eke
Sat Apr 27, 2019 8:29 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 117
Views: 7603226

Re: Questions on writing a new Mega CD emulator

I will try to answer some of your questions later since I faced similar interrogations when adding Mega CD support in Genesis Plus GX but regarding pending int being cleared when disabled, that's something that was needed in Genesis Plus GX to fix some games freezing in some cases (hence the comment...
by Eke
Sat Apr 27, 2019 6:42 am
Forum: Megadrive/Genesis
Topic: Z80 bus + I/O mapping redux
Replies: 7
Views: 13318

Re: Z80 bus + I/O mapping redux

That's a lot of questions and they adress so many different things... I guess I will pick this one But if a game writes to byte to a10002, what happens? The 68K used in the Genesis per 68000UM.pdf states that D8-D15=D0-D7 for byte writes, and that A0 isn't used. Do the I/O ports bother to check /LDS...
by Eke
Thu Dec 13, 2018 6:25 am
Forum: Controls
Topic: Every peripheral ID?
Replies: 6
Views: 9682

Re: Every peripheral ID?

The numbers (1-8) actually refer to panel number in Activator manuals: 1 corresponds to the panel in front of the player then, in clock order, 2, 3, etc One of the manuals can actually be still found here: http://www.segakore.fr/media/segakore/downloads/systemes/activator_game_guide_u.pdf From my ol...
by Eke
Sun Nov 25, 2018 9:09 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 865
Views: 2150588

Re: New Documentation: An authoritative reference on the YM2612

Nemesis tested the address/data ports relation some years ago http://gendev.spritesmind.net/forum/viewtopic.php?f=24&t=386&start=410 It turns out that writing to an address register stores both the written address, and the part number of the address register you wrote to. You can then write to eithe...
by Eke
Mon Nov 19, 2018 8:25 pm
Forum: Megadrive/Genesis
Topic: Looping access from 68K and Z80
Replies: 25
Views: 29747

Re: Looping access from 68K and Z80

if 68K->Z80->68K was access thought buses it will lock the system at any access not only on VPD access, correct? As said previously, ZA15 is forced low when 68k is accessing Z80 bus so it's not possible to access 68k bank in Z80 memory map upper area ($8000-$FFFF) from 68k since it becomes a mirror...
by Eke
Sun Nov 18, 2018 8:15 pm
Forum: Megadrive/Genesis
Topic: Looping access from 68K and Z80
Replies: 25
Views: 29747

Re: Looping access from 68K and Z80

Well, I/O chip only connects VA1-VA7 and ZA1-ZA7, the rest of address lines are managed by the Bus Arbiter so the most logical is that it sets ZA0 according to !LDS, ZA8-ZA14 with VA8-VA14 and simply forces ZA15 low to prevent access to Z80 bank area, just like it sets VA15-VA23 with bank register s...
by Eke
Sat Nov 17, 2018 5:25 pm
Forum: Megadrive/Genesis
Topic: Looping access from 68K and Z80
Replies: 25
Views: 29747

Re: Looping access from 68K and Z80

Taken both quotes together, it sounds more like the 68000 map decodes mirrors of A00000 for z80 ram, and mirrors of A04000 for FM, and nothing else. He's not sure it does anything at all for the bank address, and freezing for VDP space could just be the mapper not asserting DTACK for an unmapped lo...
by Eke
Fri Nov 16, 2018 11:12 pm
Forum: Megadrive/Genesis
Topic: Looping access from 68K and Z80
Replies: 25
Views: 29747

Re: Looping access from 68K and Z80

Z80 32KB address space is mapped to A0xxxx on 68K. Can Z80 access to its own space using A0 page in upper 32KB? Will it stop 68K while access itself address space because it uses outer loop through 68K? The same opposite question: Z80 has special map of VDP+PSG to 7Fxx address. Can 68K access VDP/P...