Search found 94 matches

by byuu
Wed May 22, 2019 7:34 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

it seems like the CDD status is initialized then stays to 0x0 (stopped) until a TOCT request command is sent (0x2:0x4), which only then causes a CDD status transition to 0x9 (read TOC) if there is a disc in the tray (0xb otherwise). Ah, so then ... how does the BIOS get correct TOC information if t...
by byuu
Tue May 21, 2019 6:09 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

After implementing more of the CDD ... Genesis Plus GX seems to start in the "reading TOC" (0x9) mode when the system is reset and a disc is inserted. The BIOS then sends a "stop" (0x1) command, which GX lets the BIOS read back once, and then it switches to "reading TOC" mode again. I don't see any ...
by byuu
Tue May 07, 2019 8:13 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

nobody has shared CD images that attempt to do so. Indeed, I really need some examples of sectors in the full channel frame format and in the final decoded format, so that I can try to implement these conversion functions. I don't even have example data of what CIRC encoded bytes should even look l...
by byuu
Mon May 06, 2019 8:46 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

A thing I've promoted in higan via icarus for a long time now is a separation of concerns: We should have one set of archival images: things in an optimal, clean format with as consistent-as-possible SHA256 sums so that we ensure the data is not lost. And we should also have emulator images: things ...
by byuu
Sun May 05, 2019 4:25 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

I'm trying to build a support function library to transform between F1 frames and channel frames. So far, I have EFM working in both directions (hopefully with no table transcoding errors), scrambling working (although I don't have any test scrambled data to verify I implemented it right ...), EDC g...
by byuu
Sat May 04, 2019 2:08 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

I'm not opposed to splitting the subcode data, but my question is then, where do we stop? Should we split data sectors' 304 bytes of extra data to take 2352-byte sectors to 2048-byte sectors, and then have a separate .ecc file? They would probably compress better without the error correction data. T...
by byuu
Sat May 04, 2019 5:49 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

You are correct that TOC is stored in q-channel within the lead-in. Pretty sure the cd ripper programs that extract subchannel data don't even include this, but that info is stored in the cue file to be recreated. So then as I presume the Mega CD BIOS expects to be able to read the raw TOC data, it...
by byuu
Fri May 03, 2019 4:45 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

Could someone with a working Sega CD emulator please share a CDC + CDD command log for booting a game from the BIOS? Just up to the game running its own loaded code would be perfect. What I see right now is: CDC: 0xF RESET CDC: 0xF RESET CDC: 0x1 IFCTRL CDC: 0x8,0x9 WA CDC: 0xC,0xD PT CDD: 0x0 NOP C...
by byuu
Fri May 03, 2019 12:31 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

Okay, here's my implementation of the graphics ASIC without look up tables. Many thanks to the Genesis Plus GX code for this. I feel like there's ways to simplify it more ... First thought was store a mapMask of 0xffffff when stamp.repeat=0, save the conditional and mask on load from vector table + ...
by byuu
Fri May 03, 2019 6:16 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

I don't want to promise the world here, but ... if I can get the Mega CD supported, and I can get all of the requisite information and content to emulate the Mega LD, then I'm all for supporting that as well. I was very happy to learn you were working on preserving those games. I've looked all over ...
by byuu
Thu May 02, 2019 5:59 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

I really don't have a clue how to emulate this. The big mystery to me is, how do regular CPU reads and writes work? If it's really just the work RAM being slow, wouldn't it take just a touch too long to respond to regular reads as well? And even in the case of DMA, won't the address lines get increm...
by byuu
Thu May 02, 2019 4:49 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

That was it, thank you Sik and Eke! https://i.imgur.com/RJsVbrgm.png Man, I keep thinking this system can't get any flakier and yet it keeps managing to impress me. I have no clue how to emulate this cleanly. I can't implement it as a one-time action inside writes to VDP register 1 (which sets the D...
by byuu
Wed May 01, 2019 7:48 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

It could very easily be a bug elsewhere in the Mega Drive emulator. I would have thought if DMA were broken that we'd have an issue with most cartridge-based games, and yet I'm not currently aware of any. Granted I have not extensively tested the library. But if it's specific to just Mega CD word RA...
by byuu
Wed May 01, 2019 2:14 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

Well, I almost have graphics working (pretty much directly lifted from Genesis Plus GX for now, extremely helpful code!) But one last issue is kicking my tail again >_> https://i.imgur.com/kXjqtEDm.png Larger: https://i.imgur.com/kXjqtED.png Gone over the code like 50 times. I'm sure it's a simple m...
by byuu
Wed May 01, 2019 1:29 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 17421

Re: Questions on writing a new Mega CD emulator

Thank you very much, this is incredibly useful information. Don't mind the shortcuts with the registers, if it works it works. I just wanted to confirm them before copying the same approach ^-^;; In unrelated news, I looked into the 4-bit MCU more. The Sega CD model 2 uses the NEC uPD75006G. Unfortu...