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by TmEE co.(TM)
Sat Aug 22, 2020 5:02 am
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

That's something I didn't know, I mainly only commented among the actual consoles (except MD2 VA2, which I would like to get and a VA0 MD1). Discrete YM3438 has longer busy bit cycle from what I remember reading from nukeYKT core notes, compared to 2612 and ASIC which would be another way to detect ...
by TmEE co.(TM)
Fri Aug 21, 2020 5:30 pm
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

YM3438 only appeared as a block integrated in the MD2 ASIC, which first appeared in MD1 VA7 (the awful sounding MD1s lol).
by TmEE co.(TM)
Tue Aug 18, 2020 2:56 pm
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

Originally I saw it with CRAM yeah, but dedicated test used VRAM DMA. I will dig up the stuff hopefully in not so far future, there's currently bunc hof work stuff getting in the way (retro PC sound hardware stuff)...

I haven't actually ever experienced the DMA bug you describe.
by TmEE co.(TM)
Mon Aug 17, 2020 9:12 pm
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

Originally I saw it when I was doing very precise raster effects, where DMA triggering was in two writes to win time, but with Z80 running I noticed that I had failing DMAs every once in a while (in that case palettes didn't get updated). Then I made a specially crafted thing, where I deliberately s...
by TmEE co.(TM)
Sun Aug 16, 2020 4:16 pm
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

DMA doesn't fail and load garbage, it is outright cancelled, the transfer does not happen and you can measure the time won from that and determine if DMA happened or not, or read VRAM instead.
by TmEE co.(TM)
Sat Aug 15, 2020 1:40 pm
Forum: Megadrive/Genesis
Topic: List of every detectable difference in Mega Drive revisions?
Replies: 17
Views: 2396

Re: List of every detectable difference in Mega Drive revisions?

There is some small difference in timing of Z80 bus crossings between MD1 VA0...MD2 VA3 (MD1 chipsets, 315-5487/5660/5700/5708), MD1 VA4/Genny3 VA1(515-5960) and Genny3 VA2(315-6123). No clue about MD2 VA2.x with 315-5685/5786, I have none to play with. I was exploring what happens when DMA was done...
by TmEE co.(TM)
Mon Aug 10, 2020 6:47 am
Forum: Blabla
Topic: Genesis Music Composers?
Replies: 2
Views: 1477

Re: Genesis Music Composers?

You can find a lot of them frob Battle of the Bits community : http://battleofthebits.org/
by TmEE co.(TM)
Mon Jul 20, 2020 4:48 pm
Forum: Mega/SegaCD
Topic: mcd-verificator (CD core accuracy tests)
Replies: 24
Views: 4576

Re: mcd-verificator (CD core accuracy tests)

32X does pass the audio lines on both models (cart + 32X > MD, using chip normally found in Nomad and MD2 VA3), !DTACK is supposed to be connected with a wire from IO board to CPU board but that was never installed in any of the production hardware... I guess they deemed one extra wire for a signal ...
by TmEE co.(TM)
Sun Jun 21, 2020 9:02 pm
Forum: Sound
Topic: YM2612 & distorted sound output
Replies: 7
Views: 1649

Re: YM2612 & distorted sound output

The output is a pulsetrain, with YMCLK / 144 clocks per sample and 24 clocks per pulse (with differing duty cycle and amplitude for 3438 and 2612). There's harmonic content going into MHz range in there so you need fairly good opamps to deal with it effectively. The output is also very weak and shou...
by TmEE co.(TM)
Sun Jun 14, 2020 4:17 pm
Forum: Sound
Topic: YM2612 & distorted sound output
Replies: 7
Views: 1649

Re: YM2612 & distorted sound output

YM2612 and YM3438 have pulse train based outputs where all channels are sent sequentially. On 2612 the pulses are very narrow and also have fairly low amplitude while 3438 has much wider and bigger pulses, allowing for better SNR. What you see on your scope is mainly due to aliasing, when you up the...
by TmEE co.(TM)
Sun May 17, 2020 11:30 am
Forum: Megadrive/Genesis
Topic: VDP 8x16 Interlace Mode
Replies: 7
Views: 1811

Re: VDP 8x16 Interlace Mode

Possibly but these are buried into past that is many years ago...
by TmEE co.(TM)
Fri May 15, 2020 10:41 am
Forum: Megadrive/Genesis
Topic: VDP 8x16 Interlace Mode
Replies: 7
Views: 1811

Re: VDP 8x16 Interlace Mode

It is good for still images, you see markedly higher detail. When things begin to move there will be various interlacing related artifacts appearing.
Here's couple experiments I made a while ago :
http://www.tmeeco.eu/SMD/HIRES.BIN
http://www.tmeeco.eu/SMD/INTERLAC.BIN
by TmEE co.(TM)
Thu Apr 30, 2020 9:39 am
Forum: Sound
Topic: SN76489 polarity
Replies: 4
Views: 1536

Re: SN76489 polarity

There's no negative polarity on TI/VDP PSG and most other PSG type sound chips. You do get stuff settle below ground level when you highpass filter the final chip output as it is done on all hardware outside the sound chip itself. On the TI/VDP PSG, outputs start high and toggle between 0 and a high...
by TmEE co.(TM)
Sun Mar 08, 2020 11:09 pm
Forum: Mega/SegaCD
Topic: Best solution for anime VisualNovel
Replies: 3
Views: 2746

Re: Best solution for anime VisualNovel

When you play CDDA you lose access to the CD drive more or less so whatever you want to show will have to fit in the RAM, and you have limited amount of that.