Search found 773 matches

by Nemesis
Fri May 23, 2008 5:32 am
Forum: Pico
Topic: Emulating Sega Pico
Replies: 33
Views: 25457

I've got a query about one thing notaz. How sure are you about the following info: The 68000 uses following hardware interrupt autovectors: level 2 - seems to be available, but most games put empty handlers here. level 3 - PCM interrupt? Probably occurs when PCM hardware needs more data, and exact c...
by Nemesis
Fri May 23, 2008 4:55 am
Forum: Pico
Topic: Emulating Sega Pico
Replies: 33
Views: 25457

I think you'll find the PCM chip is the Sega branded 315-5641. It takes all 16 data lines (which according to the memory map the PCM chip does), and it's the only device on that board I can't identify.
by Nemesis
Wed May 21, 2008 4:22 am
Forum: Sound
Topic: PCM Playback on PSG
Replies: 10
Views: 21282

I wasn't aware of the specs for the MSX; I've never looked into it. Well, reading the thread on the MSX forum, it looks like they had the same problem initially. The initial implementation took 447 T-cycles for each sample, giving a max of around 8KHz playback. Obviously they managed to improve on t...
by Nemesis
Wed May 21, 2008 3:15 am
Forum: Sound
Topic: PCM Playback on PSG
Replies: 10
Views: 21282

Wow, that sample is impressive. I wonder if the Z80 in the Mega Drive would be fast enough to make the changes at the required rate though. At 44.1kHz, the Z80 would only have around 27 cycles to update each channel. That's 27 cycles to load the next sample data from the source, and write it to the ...
by Nemesis
Tue May 20, 2008 2:22 pm
Forum: Mega/SegaCD
Topic: Technical Manuals location
Replies: 8
Views: 6920

Christuserloeser wrote:
Nemesis wrote:And as a sidenote, it seems the URL tag doesn't work, and we can't use HTML in posts, so I can't see any way to create a link to a URL that has a space in the path. :?
You could use %20 for spaces. I can't remember what works with brackets though.
Thanks, I didn't think of that.
by Nemesis
Tue May 20, 2008 2:18 pm
Forum: Mega/SegaCD
Topic: Technical Manuals location
Replies: 8
Views: 6920

Oh, you're the guy who did the transcriptions. Kudos for that man. That must have been a hell of a lot of work. Personally, I find I tend to prefer to read from the original scans, but there's one thing the transcriptions are invaluble for, and that's ctrl+f. I've considered doing a new transcriptio...
by Nemesis
Tue May 20, 2008 2:12 pm
Forum: Mega/SegaCD
Topic: Technical Manuals location
Replies: 8
Views: 6920

Yeah, I've got the transcription. Still, it's nice to have the reassurance of the original scans to refer to. In that many pages, there has to be at least one typo.
by Nemesis
Tue May 20, 2008 1:59 pm
Forum: Mega/SegaCD
Topic: Technical Manuals location
Replies: 8
Views: 6920

As of this exact moment they're uploading, but the following links will work in a couple of hours: http://nemesis.hacking-cult.org/MegaDrive/Documentation/Sega_Genesis_Manual.zip http://nemesis.hacking-cult.org/MegaDrive/Documentation/Sega_CD_Manual.zip http://nemesis.hacking-cult.org/MegaDrive/Docu...
by Nemesis
Tue May 20, 2008 1:01 pm
Forum: Video Display Processor
Topic: VDP registers timings
Replies: 34
Views: 24585

[here's how I once retrieved the correct value, your formula is not correct as it has nothing to do with 50hz/60hz: one line is approx. 63.69 us hdisplay is 63.69*256/342 = 47.67 us (same for both modes) this gives you : H32 (worst case is 8 words for VRAM) : 47.67/8 = 5.96 us H40 (worst case is 10...
by Nemesis
Tue May 20, 2008 4:13 am
Forum: Video Display Processor
Topic: VDP registers timings
Replies: 34
Views: 24585

About the FIFO, the documentation give the max number of permitted CPU access to V-RAM by line (btw, data rate is likely the dma rate) , as well as the max waiting time for the FIFO to execute one command, did you figured the exact slot timesharing between VDP & CPU ? Can we consider taht a VRAM wr...
by Nemesis
Mon May 19, 2008 12:17 am
Forum: Video Display Processor
Topic: VDP registers timings
Replies: 34
Views: 24585

Writing to CRAM during frame will cause some colored dots appear... I have no idea what happens when other things are written to. Oh, just to confirm, after thorough testing, the only kind of access to the VDP which causes these kind of glitches that I've observed are writes to CRAM. Registers, VRA...
by Nemesis
Mon May 19, 2008 12:02 am
Forum: Video Display Processor
Topic: VDP registers timings
Replies: 34
Views: 24585

Actually, the dots that appear are the colour of the value you write. Essentially, when you write to CRAM, the single pixel that is being drawn at that moment displays the colour you were writing to the CRAM at that moment, regardless of the colour that should have been displayed. This occurs even w...
by Nemesis
Mon Mar 10, 2008 9:04 pm
Forum: Cartridge
Topic: The not so famous /YS signal
Replies: 28
Views: 17600

If you're interested, the oscilloscope I'm using is the Hantek DSO 2150. You can view the product on their website at http://www.hantek.com.cn/english/produce_list.asp?unid=63 It's a dual-channel Digitial Storage Oscilloscope, with completely PC-based controls. It has a pretty high sampling rate, an...
by Nemesis
Mon Mar 10, 2008 1:04 am
Forum: Cartridge
Topic: The not so famous /YS signal
Replies: 28
Views: 17600

Just wanted to let you know, I was doing some much more thorough testing on this matter, and I got some results which contradicted tests I'd done previously. This was about 4 days ago now. I've been trying to get the time to go back and complete my testing, but I don't have a lot of free time right ...
by Nemesis
Tue Mar 04, 2008 10:24 am
Forum: Cartridge
Topic: The not so famous /YS signal
Replies: 28
Views: 17600

Wow, I took awhile to write that. Your post wasn't there when I started. If you read further: .... It is clearly stated that acknowledge cycle only occur when the interrupt is not masked, and this seems logical to me, it is how most processors are working... Hmm. Well, it does seem to suggest that, ...