Search found 773 matches

by Nemesis
Sun May 05, 2019 1:57 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 43
Views: 8291

Re: I'm officially building a microcode-level 68000 core

Tool generated would certainly explain why it's so incomprehensible, thanks for taking a look.
by Nemesis
Sat May 04, 2019 11:06 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

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. ...
by Nemesis
Sat May 04, 2019 10:34 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

If you can get three or more rips of each disk (preferably more like five or six), you can reconcile these errors and cancel them out, to get a true image of the disk as it really is, apart from surface damage or smudges on the disk surface that are interfering that is. If you can get three or more...
by Nemesis
Sat May 04, 2019 12:39 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

What Eke says is true, and no existing games rely on subcode data, but if you want to emulate/preserve the hardware itself rather than just the games, and if you want to support homebrew, all the subcode data is made available to programs running on the system, and should be properly supported for c...
by Nemesis
Sat May 04, 2019 9:25 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

Well, you know me (probably, anyway.) I've already dealt with this and the unacceptable way Famicom Disk Images are currently stored, I'll handle this the same way. I'll support a new image format that contains all data: lead-in, pregap, postgap, lead-out, subchannel data, etc in scrambled form. Un...
by Nemesis
Sat May 04, 2019 8:30 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

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 Nemesis
Sat May 04, 2019 6:06 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 43
Views: 8291

Re: I'm officially building a microcode-level 68000 core

Does anyone here know how to get in touch with Olivier Galibert? I've found he's put together... something at https://github.com/galibert/m68ksim , but there's no comments, no readme, no documentation of any kind, and apparently no reference to it anywhere on the internet. There's also a bit of a fo...
by Nemesis
Sat May 04, 2019 12:08 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

I'll add that you're right though, the lead-in and lead-out areas "degenerate" towards the edges, as the laser power level drops from the writing process. For the MegaLD images, I'm reconstructing the full data to the edges from the known data before it starts fading.
by Nemesis
Sat May 04, 2019 12:05 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

The next level down from this that I consider "valid" is to store data with the frames decoded and PQ error correction already performed, but with mode 1 sectors still scrambled and ECC/EDC correction not yet applied, and the subchannel data retained. All that you've done here is to decode the fram...
by Nemesis
Fri May 03, 2019 11:59 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

I'm gonna laugh if we end up redumping every single CD from scratch using a Mega CD/LD simply because it's capable of dumping all that. It's probably going to happen actually. The work that's been done with the Domesday Duplicator ( https://www.domesday86.com/?page_id=978 ) I expect will probably p...
by Nemesis
Fri May 03, 2019 10:25 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

Speaking of, where exactly is the TOC? If my reading up on CD formats is correct, is this part of the ~150-sector lead-in, repeated throughout it, and something that needs to be recreated from the CUE file? (well, not that we'd have to create the exact bits on the disc, just return the correct info...
by Nemesis
Fri May 03, 2019 11:35 am
Forum: Megadrive/Genesis
Topic: I'm officially building a microcode-level 68000 core
Replies: 43
Views: 8291

I'm officially building a microcode-level 68000 core

I've flirted with the idea of doing this on and off for years now, but this evening I've decided I'm going to focus on a microcode-level 68000 emulation core, and I'm going to continue with it until it's a reality. The sheer amount of data and work involved in this space feels a bit overwhelming rig...
by Nemesis
Fri May 03, 2019 5:22 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

I should mention, I also know of two people who have a bunch of official docs, containing lots of technical bulletins that have never been scanned/released publicly before. I'm hoping to be able to get at least one of them to scan and share these documents at some point in the near future, as there ...
by Nemesis
Fri May 03, 2019 5:16 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 114
Views: 14234

Re: Questions on writing a new Mega CD emulator

While MegaCD emulation is still very much on my to-do list, I have compiled a fair few resources for it over the years. There's one largely untapped resource you should take a look at. I own a couple of these Cross Product MegaCD dev units: https://segaretro.org/SNASM_Mega-CD . This has as part of i...
by Nemesis
Fri Apr 26, 2019 5:43 am
Forum: Exodus
Topic: Load roms externally?
Replies: 6
Views: 1382

Re: Load roms externally?

One thing that makes it slightly more complex is how ROM loading works. Exodus can't actually load a ROM. A ROM is just a blob of arbitrary data. Out of context, it means nothing. Exodus doesn't have anything about a Mega Drive hard-coded at all, as the system itself is just defined by a bunch of po...