Search found 27 matches

by Kabuto
Thu Nov 09, 2017 3:48 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 370318

Re: New Documentation: An authoritative reference on the YM2612

I can confirm this large ladder gap from measurements of DAC output levels: https://docs.google.com/document/d/e/2PACX-1vQ6CEUtCM3U6KKFD3i4lbMaF8muGQ5dez27OcpZOWRP2GgJviklr9rLIQut-LdoGfU4InazlIcbCvlG/pub (scroll down to YM2612 and zoom in on those 2 diagrams). Also, further discontinuities exist, es...
by Kabuto
Sat Apr 29, 2017 12:52 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Cool :)

Regarding those remaining glitches, please check what I wrote here about re-fetching of sprite Y coord and size:
viewtopic.php?f=22&t=2604&start=15#p31287

Looks like it affects your emulator as well
by Kabuto
Sat Apr 29, 2017 8:47 am
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Eke wrote:Strange. This is what I got, not sure where this comes from...
This looks like you still need to invert address bit 0 after converting the target address for 128k mode emulation.

No idea what causes the vertical stripes in the 3rd pic, though, incorrectly emulated illegal plane modes maybe?
by Kabuto
Thu Apr 27, 2017 8:31 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

I've been meaning to do some proper tests (though I'm sure someone else already has at some point), but it's good to have another data point. IIRC invalid horizontal size always gives you 32x1, invalid vertical size with valid horizontal size will behave as if vertical size was set to 32. On an unr...
by Kabuto
Thu Apr 27, 2017 12:26 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Another possible issue: subsequent link field writes are done shortly before the sprite table address is changed. If this word is emulated to be written out too late then your emulated VDP might see it as not being written to the current sprite table as its address will have changed by then. As a re...
by Kabuto
Wed Apr 26, 2017 11:05 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Yes, this code does indeed try to avoid FIFO stalls so the Z80 would not be halted when trying to prefetch. Actually, getting the timing right was not that difficult, I just adjusted NOPs until I got no more FIFO stalls (measured indirectly because FIFO stalls stabilise the timing on screen as measu...
by Kabuto
Tue Apr 25, 2017 7:52 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

1) no per column vscroll changes here, just per rasterline vscroll changes in the zoomer, no vscroll changes at all when it twists 3) yeah, this part requires halfway precise timing (but it's actually kinda relaxed since this routine also has to account for cycles stolen by the Z80) 4) we call them ...
by Kabuto
Mon Apr 24, 2017 6:14 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

I have another question regarding the debug mode when sprite plane is forced active (bits 8,7 = 0,1) : what happens for pixels where there hasn't been any sprite pixel (transparent or not) rendered in the line buffer ? The sprite buffer pixel color value is normally 0 in this case (same as a low-pr...
by Kabuto
Sun Apr 23, 2017 4:15 pm
Forum: Demos
Topic: wolfenstein demo for sega genesis
Replies: 361
Views: 130604

Re: wolfenstein demo for sega genesis

Awesome progress! Just wanted to point out the byte granularity DMA trick as explained in here , it might or might not give you a speed boost, depending on how your rendering works. All mega drives support it in one way or another, and some emulators already emulate it as well. MD1 and MD2 do as des...
by Kabuto
Sat Apr 22, 2017 11:17 am
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Some questions about V28/V30 bit trick': - it makes HINT still occurring during vborders but also whole vblank i.e all 313 lines possibly ? yes. HINT runs continuously. Set register $F to 0 and you get a HIRQ on each of the 313 rasterlines. Set it to 156 and you get a HIRQ before raster line 156 th...
by Kabuto
Sat Apr 22, 2017 1:20 am
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

Lots of work was spent on getting rid of all the unwanted garbage, but 2 effect makes explicit use of what one would normally consider garbage ;) So based on a comment/question from alk on IRC, I'm guessing one of those is the dissolve of the white border in the post-Titancade screen. What's the ot...
by Kabuto
Thu Apr 20, 2017 5:08 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Re: Titan's Mega Drive tech docs including Debug Register

- Sprites processing: ... ypos and size were read a second time during "phase 2" ... This could indeed be abused to produce tricky sprite behavior but more as a way to stress emulators than improving sprites capacity so I don't know if this was used in the demo ? --> yes, that behaviour is utilised....
by Kabuto
Wed Apr 19, 2017 6:20 pm
Forum: Video Display Processor
Topic: Titan's Mega Drive tech docs including Debug Register
Replies: 36
Views: 9910

Titan's Mega Drive tech docs including Debug Register

This is our first item in a series of follow-ups about the making of Overdrive 2: everything we figured out about the Mega Drive hardware. I hope this will clear many things up and inspire more people to play with this platform! Just ask right here on the boards if there are any questions, or join u...
by Kabuto
Sun Dec 14, 2014 10:01 pm
Forum: Demos
Topic: wolfenstein demo for sega genesis
Replies: 361
Views: 130604

During "Overdrive" development we ran across a strange DMA related bug which later went away after a rewrite of that code section, but nonetheless I did some digging to find it, following an IRC chat. The code in question initiated CRAM DMA with pre-loaded registers as in "move.l d7, (a6)" (d7 = $C0...
by Kabuto
Sun Dec 07, 2014 2:08 pm
Forum: Exodus
Topic: Bug reports?
Replies: 48
Views: 18382

Exodus seems to be about the only emulator that denies 68k -> z80 bus accesses while the z80 bus isn't fully acquired yet - pretty nice for debugging. But there's an implementation bug. In my case I'm just using z80 instructions with 4T maximum, so theoretically the 68k just needs a pause of 11 cycl...