Search found 860 matches

by Sik
Wed May 01, 2019 7:38 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 7621

Re: Questions on writing a new Mega CD emulator

Everything looks shifted by one word… you sure it isn't a DMA problem rather than ASIC? I recall there's a pretty big problem with DMAing from word RAM where the first access wouldn't be correct and games had to compensate for it. Forgot the exact details tho, although it should show up somewhere in...
by Sik
Wed May 01, 2019 5:01 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 7621

Re: Questions on writing a new Mega CD emulator

In light of that, the JVC X-Eye seems to be our best shot. That uses the Hitachi HD404019, which does seem to have a program read-out mode. But we would be analyzing a third-party hardware system instead of something from Sega themselves. It could still lead to some insights, like what if anything ...
by Sik
Mon Apr 29, 2019 4:00 am
Forum: Megadrive/Genesis
Topic: Z80 bus + I/O mapping redux
Replies: 7
Views: 1023

Re: Z80 bus + I/O mapping redux

For TMSS, I am mapping a11400 + a11402 and only recognizing word writes. No mirroring is done. $A14000 and $A14002 :​P I don't know how to emulate a11000 yet (ROM/DRAM cartridge select), and I don't know what happens on reads, or how it affects timings. For now, it doesn't seem super important to w...
by Sik
Sat Apr 27, 2019 3:34 am
Forum: Megadrive/Genesis
Topic: Z80 bus + I/O mapping redux
Replies: 7
Views: 1023

Re: Z80 bus + I/O mapping redux

byuu wrote:
Fri Apr 26, 2019 1:42 pm
Sometimes I read that a10000-a10fff (12-bit range) is really just a10000-a100ff (8-bit range.) Might these blocks go further and fill in bxxxxx as well?
It doesn't, $B00000-$BFFFFF hang up the bus access (unless the cartridge itself decides to assert /DTACK to let it proceed).
by Sik
Sat Apr 27, 2019 2:38 am
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 7621

Re: Questions on writing a new Mega CD emulator

*Super* bizarre the Z80 can write to the main 68K's CPU RAM, but not read from it, meh. Seems like they tried getting it to work but couldn't fix it in time, from what I recall the problem is that some signals end up with the wrong timing and hence the Z80 ends up seeing garbage? (also don't get fo...
by Sik
Thu Apr 25, 2019 11:47 pm
Forum: Mega/SegaCD
Topic: Questions on writing a new Mega CD emulator
Replies: 112
Views: 7621

Re: Questions on writing a new Mega CD emulator

And that thing the CDC documentation does with the /BIT settings (eg logic low = enable/active, logic high = disable/inactive) is the most maddening thing in the world. Name the damn variables the inverse. If it's /ENABLE then call it DISABLE. It makes it so much more difficult when I have to perfo...
by Sik
Thu Apr 25, 2019 4:21 pm
Forum: Sound
Topic: Some beginner questions concerning YM2612
Replies: 24
Views: 2646

Re: Some beginner questions concerning YM2612

Angles, or derivates (i.e. tangent of angles) ? That's more the meaning of "rate" for me (and it is different if angle isn't small). I know very few bout electronics, but I guess a device full of oscillators may not have much more difficulties in handling trigonometrics functions than simple accumu...
by Sik
Thu Apr 25, 2019 5:07 am
Forum: Demos
Topic: MD-NICCC - a 3D Mega Drive experience by TiTAN
Replies: 56
Views: 4946

Re: MD-NICCC - a 3D Mega Drive experience by TiTAN

The VRAM equipped on the Mega Drive is 8-bit though, so VRAM writes take twice as long as CRAM and VSRAM writes do. That's precisely why 128KB VRAM would have been awesome: what that mode does is set the VRAM bus to 16-bit instead, which in turn doubles the bandwidth (not just the available memory)....
by Sik
Wed Apr 24, 2019 9:56 pm
Forum: Demos
Topic: MD-NICCC - a 3D Mega Drive experience by TiTAN
Replies: 56
Views: 4946

Re: MD-NICCC - a 3D Mega Drive experience by TiTAN

Yes, you do. MD has more VDP bandwidth than the SNES homonym, nearly twice if my memory serves me well. They even go to only 50hz (PAL) to maximize it. That's what really counts on this demo. Um, wrong, even assuming H40, the bandwidth is only somewhat larger (around 7KB vs around 6KB, if memory se...
by Sik
Wed Apr 24, 2019 1:09 pm
Forum: Demos
Topic: MD-NICCC - a 3D Mega Drive experience by TiTAN
Replies: 56
Views: 4946

Re: MD-NICCC - a 3D Mega Drive experience by TiTAN

Yeah, but the SNES version was also using precomputed polygons instead of any 3D calculations (the challenge was to recreate the demo using its original data and that data was already in 2D format), so that excuse still doesn't apply. This is also why MD-NICCC was letterboxed, the source material is...
by Sik
Wed Apr 24, 2019 12:59 pm
Forum: Super 32X
Topic: Using 32x as a 3rd plane, possible?
Replies: 28
Views: 3867

Re: Using 32x as a 3rd plane, possible?

Unless you set RV=1, in which case the 68000 mapping is mostly¹ restored (albeit the SH-2s won't be able to access cartridge area until RV becomes 0 again). Not useful if you want the SH-2s to access ROM tho. ¹The 68000 vectors keep pointing to the banked area so you still need to account for that, ...
by Sik
Wed Apr 24, 2019 12:54 pm
Forum: Sound
Topic: Some beginner questions concerning YM2612
Replies: 24
Views: 2646

Re: Some beginner questions concerning YM2612

The limit for AR is 31 tho. It's also instantaneous in that case anyway (since it's the maximum value). Also AR/DR/SR/RR all represent slopes (i.e. the angles). Not sure the exact way to measure them, but higher value = steeper slope (and 0 = stays flat… something you should probably avoid in AR's c...
by Sik
Sat Apr 20, 2019 1:13 am
Forum: Video Display Processor
Topic: Help scale and rotation sega genesis
Replies: 33
Views: 3915

Re: Help scale and rotation sega genesis

I forgot, are the possible switch points even contiguous or are they spread over a few pixels? Because if the latter that reduces the possible split points that won't cause trouble even more. We're talking about something that needs to be cycle perfect here. I guess DMA bitmap could help give some i...
by Sik
Thu Apr 18, 2019 5:37 pm
Forum: Cartridge
Topic: Size limits
Replies: 35
Views: 7288

Re: Size limits

Wait, it's for that shmup where you were using a map photo for the background? I mean, huh, dunno, but maybe it'd be better for you to use pixelart and reuse tiles as needed. There's no reason why you should be spending that much on a scrolling background unless you go full Silpheed with its prerend...
by Sik
Wed Apr 17, 2019 7:40 pm
Forum: Video Display Processor
Topic: Help scale and rotation sega genesis
Replies: 33
Views: 3915

Re: Help scale and rotation sega genesis

In terms of DMA transfer, you end up using the same time yeah (transferring a 256px wide buffer in H32 mode will take as long as transferring a 320px wide buffer in H40 during vblank). What you reduce is CPU usage when doing software rendering — in particular, you only need to render 80% as many pix...