Search found 256 matches

by TascoDLX
Sat Jun 09, 2012 6:55 am
Forum: Megadrive/Genesis
Topic: m68k subtraction and absolute value
Replies: 18
Views: 5789

So I attempted to port this: http://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm#Simplification over to the genesis but for some reason it does not work correctly I have looked at each line of code at least 10 times each if not more and I can not understand what the problem is. In general, if...
by TascoDLX
Wed May 23, 2012 4:55 am
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

What I don't understand is what triggers those CDC host reads. I guess it's initially coming from a ROMREADxxx command sent to the BIOS but I can't seem to find what make the BIOS initialize CDC (CDCSTART command ?), enable buffer RAM writes for a few sectors then suddenly stop it (CDCSTOP command ...
by TascoDLX
Tue May 22, 2012 8:18 am
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

Excellent! In that case, I will add that I now have a fully working PAC -- Thanks to BlueBMW -- so I should be able to do minor testing should the need arise. Otherwise, I await the continued dumping efforts of Nemesis. ;)
by TascoDLX
Tue May 22, 2012 8:07 am
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

Well, I was wrong: in fact, running opcode by opcode does not make any good, the only thing that somehow made it go past the black screen on startup was to significantly increase either the number of SUB-CPU cycles executed per line (I forgot I still had this slightly modified in my previous test.....
by TascoDLX
Sun May 06, 2012 12:37 pm
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

So what you mean is that there is actually two values for DMNA, the one that can be read and the one that is written ? Yes, I would say there are different values across the board. As far as reads go: - RET and DMNA in 2M mode reflect the wordram assignment as usual. - RET bit in 1M mode reflects t...
by TascoDLX
Sat May 05, 2012 9:45 pm
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

I also have a question regarding Word-RAM and mode switching: to which part is assigned Word-RAM when switching from 1M to 2M mode ? I assume that if RET bit is set as well, it is set to MAIN-CPU side but is it the default ? What if RET bit is not set when MODE bit is changed from 1 to 0 ? Basicall...
by TascoDLX
Sun Apr 22, 2012 9:06 pm
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

That would be correct if that was to describe 32x32 mode - you need 4 horizontal 8x8 tiles to get 32x32 pixels. However, to make 16 horizontal pixels, you would need four 4x4 tiles. Hopefully any of that made sense. That would make a whole lot more sense if there was such a thing as a 4x4 tile. :P ...
by TascoDLX
Sun Apr 22, 2012 8:39 pm
Forum: Mega/SegaCD
Topic: Scaling hardware?
Replies: 84
Views: 32699

The stamps themselves are NOT laid out like tiles in the MD - the 16x16 stamp is actually laid out as sixteen 4x4 tiles. Each tile is like this 0 1 2 3 4 5 6 7 8 9 A B C D E F That doesn't sound right. Those should be 8x8 tiles (according to the manual). Otherwise, your description of the layout is...
by TascoDLX
Wed Apr 18, 2012 5:30 pm
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

(Tasco, your pac ended up being a LOT worse than it originally appeared to be! I'll get you pics later on. Dont worry, it'll be good when I'm done :) ) Cool. You are the man! Can't wait to see. ;) Also, I had a thought... It might be better to tap the LD video before it even reaches the chip where ...
by TascoDLX
Mon Apr 16, 2012 3:10 pm
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

Based on what I've seen, I would set the same value to 0138 as you do for 0139. I haven't found where 0138 is set, but I'm sure it's there somewhere. The settings I gave for 0139 should be correct.
by TascoDLX
Mon Apr 16, 2012 2:32 pm
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

I think I missed a call for you. 0130 [A0] should set the volume to the correct level. SB is constantly setting the volume with this call, so I don't know if the value gets reset somewhere and this is how they counter it. The video streams A & B should be basically the same, except only one of them ...
by TascoDLX
Fri Apr 13, 2012 11:58 am
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

SHOOT THEIR PHASERS! :D Here's my scouting report for Space Berserker. As far as the data goes, it's just like an ordinary CD game. In fact, Space Berserker uses the same basic disc read routines as at least one other game: Lethal Enforcers. (There are probably a few others that use that code, but I...
by TascoDLX
Sat Apr 07, 2012 5:36 am
Forum: MegaLD
Topic: Emulating Pioneer LaserActive (Mega-LD) games
Replies: 189
Views: 86872

I've finally fixed my dumper program! Huge thanks to TascoDLX for all his help. It's 1AM in the morning here right now, so I won't upload a full iso image of Space Berserker just yet, but watch this space! I'll also work more on the process for ripping the analog video and get that uploaded here in...
by TascoDLX
Tue Mar 20, 2012 8:45 am
Forum: Megadrive/Genesis
Topic: M68000 Microcode-level emulation
Replies: 18
Views: 22095

There's loads of information at www.z80.info, but I'm not entirely sure it gets as detailed as you'd like it. Maybe it's buried somewhere in there -- I don't have much time to go digging. I remember seeing a bit of info on the Z80's T-states within each M-cycle, but nothing comprehensive.
by TascoDLX
Mon Mar 19, 2012 7:07 am
Forum: Megadrive/Genesis
Topic: M68000 Microcode-level emulation
Replies: 18
Views: 22095

In case you missed it, M68000 microcode/nanocode was briefly discussed here . The M68000 patents are very thorough -- mind-numbingly so. They include all the nanocode (see US Patent 4,325,121 ) , somewhat distorted, but nevertheless spot-on. Must be read carefully, though. See also US Patents 4,296,...