Search found 254 matches

by TascoDLX
Thu May 23, 2019 6:43 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

Logs below ... any ideas this time? This is likely the last piece before I can boot some stuff :/ It looks like you're not performing the seek for the read command. The CDD treats the READ command as a seek leading into reading data. Contrast this with the SEEK command, which is treated as a seek l...
by TascoDLX
Sun May 05, 2019 8:21 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

Firebell pointed me at a weird issue in Silpheed that I did not understand: http://redump.org/disc/39378/ I didn't totally follow what they wrote about this either. I'll track down the image and take a look. Here's how I read it: Basically, there's a break in the data track. 7508 bytes of zero (pre...
by TascoDLX
Sat May 04, 2019 6:05 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

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? ECC is normally redundant data. Note that the 304 bytes also includes header/sync and CRC data. In most cases, all that data can be faithfully recreated. For ins...
by TascoDLX
Sat May 04, 2019 6:32 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

byuu wrote:
Sat May 04, 2019 5:49 am
If nothing can read it, is the TOC binary format encoded in the lead-in Q-channel even known at this point? ._.
http://www.13thmonkey.org/documentation ... c3r10g.pdf
see pdf page 63
by TascoDLX
Fri May 03, 2019 8:23 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

Timecode is relative to start of the mandatory data track pre-gap, which also factors into the total time, I believe. So, track 1 start will be 00:02:00, and all subsequent tracks are offset accordingly (+2 seconds). You are correct that TOC is stored in q-channel within the lead-in. Pretty sure the...
by TascoDLX
Sun Apr 28, 2019 8:07 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 5019

Re: Questions on writing a new Mega CD emulator

So it turns out the Z80 is driving the YM2612, which is where my audio is missing. It hits this routine and dies: https://github.com/DarkMorford/scd-bios ... g0.z#L1126 It seems to be a bug in the Z80 code that (remarkably) doesn't prevent the program from working properly, but you need to support ...
by TascoDLX
Thu Aug 09, 2018 5:43 am
Forum: Exodus
Topic: Incorrect disassembly of LINK instruction
Replies: 8
Views: 1242

Re: Incorrect disassembly of LINK instruction

Yeah, you don't want to be messing with formatting there. Probably going to break things. :D Actually, the existing code already has a mechanism for treating immediate data as signed, but it's a little hacky itself. Basically, all immediate data is automatically signed-extended and always disassembl...
by TascoDLX
Sat Aug 04, 2018 2:57 am
Forum: Exodus
Topic: Incorrect disassembly of LINK instruction
Replies: 8
Views: 1242

Re: Incorrect disassembly of LINK instruction

Here's the explanation... LINK does the following: - push the source register onto the stack - copy the stack pointer to the source register - fetch an immediate word - add it to the stack pointer Exodus describes the instruction using 3 parameters: source, target, and offset. Target is not specifie...
by TascoDLX
Thu Feb 05, 2015 6:12 am
Forum: Mega/SegaCD
Topic: Disassembling the Digital Pictures media codec
Replies: 15
Views: 7098

Question: How did you know that SUBCODE.BIN gets loaded at $008268? Usually I'd look at the IP/SP -- the startup code for each cpu -- and observe where files get read and copied. That may require decent knowledge of sub cpu functions (cd bios calls, etc), and the code is sometimes not obvious. It's...
by TascoDLX
Wed Feb 04, 2015 8:49 am
Forum: Mega/SegaCD
Topic: Disassembling the Digital Pictures media codec
Replies: 15
Views: 7098

It looks like the program is repointing to a location offset from address $00015DB4. I checked that area of memory using an emulator, and it's always empty. However, using all zeroes in my code leads to graphics glitches in the output. I'm stumped. Can I get some help on this? It's right under your...
by TascoDLX
Mon Dec 29, 2014 10:35 pm
Forum: Mega/SegaCD
Topic: Disassembling the Digital Pictures media codec
Replies: 15
Views: 7098

Do you have any more information on the Sega CD font generator? It's listed in the dev manual under "color calculation". - You write two 4-bit color index values to the first register ($ff804c). Call these color 0 and color 1. - You write a 16-bit bitmap to the second register ($ff804e). This gener...
by TascoDLX
Mon Dec 29, 2014 9:51 pm
Forum: Mega/SegaCD
Topic: Testing boot from CARTRIDGE SLOT at 0x400000
Replies: 14
Views: 5934

I'm currently trying to make heads and tails from LaserActive LD SUB CPU BIOS and figure out how it decides if it should or not load the MEGA-CD/SEGA-CD disc SUB CPU BIOS. Apparently I found the data it uses on the said checking but I can't figure out how it's used yet. For checking discs, the LD S...
by TascoDLX
Sat Oct 25, 2014 10:25 am
Forum: Mega/SegaCD
Topic: Disassembling the Digital Pictures media codec
Replies: 15
Views: 7098

As far as I can tell, the VRAM dump is not byteswapped. The first tiles in Corpse Killer's VRAM are a font, which is easily recognizable in a hex editor. Well, the VRAM dump you posted from Slam City is definitely byteswapped. You can tell by looking at the name table. That's the only reason I ment...
by TascoDLX
Thu Oct 02, 2014 3:28 am
Forum: Megadrive/Genesis
Topic: TMSS help.
Replies: 26
Views: 5200

Well, I have good and bad news. The good: Both ROMs work The bad: Both ROMs work How can you tell which was the fix if they both work? :S Well, they're sorta both the same fix. Writing the last VDP reg (#23) sets the DMA control state of the VDP. It's just that writing $80 doesn't change the state,...
by TascoDLX
Thu Oct 02, 2014 2:45 am
Forum: Mega/SegaCD
Topic: Disassembling the Digital Pictures media codec
Replies: 15
Views: 7098

I totally missed this post. :oops: I don't think it would be too hard, but I never really had any desire to reverse engineer the player. It depends on how much experience you have doing that and how thorough you want to be about it. I don't know how much progress you've made, but I'll take a look at...