Search found 864 matches

by Eke
Fri May 10, 2019 6:36 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

hopefully some helpful stuff towards Sega CD emulation. That's a great release, with a lot of interesting manuals but there does not seem to be any unknown Genesis or Sega CD hardware documentation in there (I can not tell for Saturn emulation though). It adds a few Genesis / Sega CD Technical Bull...
by Eke
Mon May 06, 2019 8:14 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

And it raises another question: should the subchannels be stored in the deinterleaved or in the interleaved form? They are interleaved on the CD itself and certain drives are able to output the raw interleaved subs in certain modes. For the record, Mega-CD gate-array stores subcode data in raw (int...
by Eke
Sat May 04, 2019 1:12 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

I agree, and I'm all for supporting a full image format with leadin/leadout sectors if that's ever possible to get these dumped more accurately than current TOC infos reported in cue/ccd/toc/etc files if concerned people ends up with one that is 'perfect' enough for everybody. Personally, I also hav...
by Eke
Sat May 04, 2019 11:59 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

So then as I presume the Mega CD BIOS expects to be able to read the raw TOC data, No, it doesn't. BIOS only reads the TOC data through CDD command/status. Q channel raw data is decoded by CD DSP chip and sent to CDD micro-controller (through SUBQ signal) which extracts the TOC infos from it while ...
by Eke
Fri May 03, 2019 8:44 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

There are a few interesting defines iib that file, to improve CDD emulation accuracy. ;;various timeout values IRQTIMEOUT EQU 2 ;number of ms before HSCK required after IRQ HSCKTIMEOUT EQU 3 ;number of ms to complete status/command sequence H2ITIMEOUT EQU 3 ;number of ms to wait for handshake from t...
by Eke
Fri May 03, 2019 6:47 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

Wow, this is very interesting piece of information, thank you Nemesis ! I just had a look at segaemu.asm file and it indeed seems to be direct emulation of CDD hardware (maybe more ?), including CDCK/HOCK communication protocol with gate-array, handling of commands, status responses, TOC extraction ...
by Eke
Thu May 02, 2019 2:49 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

Indeed you are right; my mistake, that would be on sub-CPU side only.
by Eke
Thu May 02, 2019 6:27 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

I really don't have a clue how to emulate this. Looking at your load() function code, you could easily emulate this by using an alternate read() function to read from cpu space, something like this (also missing mega cd hardware condition check but you get the idea): uint16 VDP::DMA::readbus(uint24...
by Eke
Wed May 01, 2019 10:06 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

I see that GPGX is caching some stuff when starting a new block render Yes, to optimize rendering, I precalculate all the parameters that remain unchanged and initialize address pointers when the gfx operation is triggered rather than recalculating or reading again everything on each line, assuming...
by Eke
Wed May 01, 2019 6:25 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

Re: Questions on writing a new Mega CD emulator

X'Eye and Wondermega1/2 BIOS are compatible with Genesis Plus GX using the exact same CDD emulation model as with other models so I don't think CDD programs are incompatible or even so much different but rather that they are all based on the same source, with some added internal functions to support...
by Eke
Tue Apr 30, 2019 8:56 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 37379

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: 114
Views: 37379

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: 114
Views: 37379

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: 114
Views: 37379

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: 114
Views: 37379

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...