Search found 248 matches

by TascoDLX
Thu Aug 09, 2018 5:43 am
Forum: Exodus
Topic: Incorrect disassembly of LINK instruction
Replies: 7
Views: 645

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: 7
Views: 645

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: 6001

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: 6001

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: 6001

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: 5160

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: 6001

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: 4553

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: 6001

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...
by TascoDLX
Thu Oct 02, 2014 1:56 am
Forum: Megadrive/Genesis
Topic: TMSS help.
Replies: 26
Views: 4553

Thanks for the useful information friend. I corrected the issues you mentioned, and now after reading some of those posts have a feeling there will be more even once this gets running on real hardware. Well... here goes nothing. https://www.mediafire.com/?l8dsi6pyiosyeqh You slightly missed the poi...
by TascoDLX
Wed Oct 01, 2014 4:17 am
Forum: Megadrive/Genesis
Topic: TMSS help.
Replies: 26
Views: 4553

Take a look at your VDP regs initialization. It's probably not a good thing that you're enabling DMA for no reason. Regardless of that, you can crash some systems by writing the DMA regs and NOT triggering DMA. If you really want to init the DMA regs (and you probably shouldn't touch them unless you...
by TascoDLX
Thu May 01, 2014 7:51 am
Forum: Mega/SegaCD
Topic: Reading subcode data on the MegaCD
Replies: 12
Views: 5058

There's no documentation on exactly when you should call the CDCSETMODE routine. I found the only time I could get it to do anything useful was if I called it for each sector, after CDCSTAT reported that a sector was available. Not to quote myself, but... "Calling CDCSETMODE doesn't change the CDC ...
by TascoDLX
Wed Apr 30, 2014 4:04 am
Forum: Mega/SegaCD
Topic: Reading subcode data on the MegaCD
Replies: 12
Views: 5058

I only skimmed your post. I'll come back to it, but this part... I also basically don't understand the way the BIOS reads, buffers, and sends sector data to my code, which doesn't help matters. What do CDCSTAT, CDCREAD, and CDCTRN actually do, in a nutshell, and where is the actual data at each stag...
by TascoDLX
Thu Feb 06, 2014 2:04 pm
Forum: Blabla
Topic: sega.doc legal issues
Replies: 2
Views: 2097

At best, the publication of so-called "confidential" information is a matter of trade secret law. The fact that the information has been public for so long (not to mention it concerns ancient hardware) effectively voids the confidentiality status and nullifies any claim to trade secret. Copyright la...
by TascoDLX
Wed Jan 08, 2014 6:25 am
Forum: Mega/SegaCD
Topic: Reading subcode data on the MegaCD
Replies: 12
Views: 5058

I finally managed to get something out of the hardware last night while testing this stuff, but I had limited time to work on it, so I wasn't able to verify my results, but still, I managed to initialize subcode reading and get something out of the SCDREAD and SCDPQ functions. I'm still not quite s...