Turbografx Emulation

[notaz]

Like a lack of horizontal interrupt support causing mid-frame palette switches to fail; classic example being water coloration taking up the whole screen in Sonic 2/3 as soon as you touched water...

You sound fairly outdated.

... the MD has 3 major components; Yamaha Ym2612 for FM synthesis, a custom sound generator previously used in the Master System, based on a Texas Instruments part, that does more basic waveforms, and a DAC. There's also the 3.58 MHz Z80 coprocessor that is typically used by games for audio handling..... pretty fancy.

Actually DAC is is a part of YM2612, and Z80 is fully emulated and should not affect audio quality as long as the timing is right (and I think it is).

 

[Exophase]

Stealth Bagel; The few times I used PicoDrive it sounded perfect, I don't think you have any business talking about it when you haven't used it in such a long time.

DaveC; This is what I can tell you about sound in my PCE emulator.. it supports DDA (direct audio) and noise. IMO in a lot of games that actually work sound sounds good, but in a few games that otherwise work fine it sounds terrible. So there are some bugs, but nothing overall missing. I'm still trying to find a game that actually uses the LFO.

It's a good thing Genesis does have that Z80 or else I don't see how it'd do digital sound at all because it has no timers, which is not good at all. It needs a CPU to sit there and poll external variables while processing audio. If it had a timer IRQ then it wouldn't need a second CPU. I think Sega's solution to everything is "throw a CPU at it" (look at Saturn).. maybe there's some other technique for games that drive it with the 68k, I dunno.

 

[Tobriand]

No; having compared the gp2X MD emulators to the real deal, a MegaDrive model 1 system, the difference is night and day.... the biggest problem is the YM2612 emulation which is quite a tricky chip to imitate effectively. Sure for a portable solution they get the job done but with all the extra CPU time at the programmers' disposal on the new handheld I'd prefer to see it shaped up a good bit.

It can't be *that* big a difference - after all, DaveC is about as close to a true perfectionist as you can get, and if *he* says he's happy, it's got to be pretty darn close!

 

[sam fisher]

The difference is probably caused by the GP2x's shitty as hell speakers.

 

[kfuse]

yea but thats a double edge sword...

both hardware have to be on equal footing for anything to be gained.

 

[halo9]

The difference is probably caused by the GP2x's shitty as hell speakers.

!
yep

 

[notaz]

It's a good thing Genesis does have that Z80 or else I don't see how it'd do digital sound at all because it has no timers, which is not good at all.

Actually there are 2 pollable timers provided by YM2612 (no irqs though, flags are set when they expire).

 

[Exophase]

It's a good thing Genesis does have that Z80 or else I don't see how it'd do digital sound at all because it has no timers, which is not good at all.

Actually there are 2 pollable timers provided by YM2612 (no irqs though, flags are set when they expire).


Yeah, I know, that's what I meant by "external variables." At least it means an emulator doesn't need super high instruction cycle accuracy just to get things sounding right..

I guess I only consider something a real timer if it generates IRQs. I can't really imagine writing code that uses timers without them, aside from wasting an entire second CPU on it.

 

[DaveC]

Stealth Bagel; The few times I used PicoDrive it sounded perfect, I don't think you have any business talking about it when you haven't used it in such a long time.

DaveC; This is what I can tell you about sound in my PCE emulator.. it supports DDA (direct audio) and noise. IMO in a lot of games that actually work sound sounds good, but in a few games that otherwise work fine it sounds terrible. So there are some bugs, but nothing overall missing. I'm still trying to find a game that actually uses the LFO.

Do you think maybe it could be of use to look at Ootake to see what is done there? Maybe it would help you find the sound bug. Ok I know it sucks to try to understand and use someone else's code, but just a thought.

It would be interesting to see though. Considering the amazing work you did on the GBA emu I would think TG would be relatively simple for you.

What is the LFO? Low Freq Oscillator?

The difference is probably caused by the GP2x's shitty as hell speakers.

They aren't that bad. They are tinny like most small devices but are clear. The F200 does sound better though.

 

[StealthBagel]

Stealth Bagel; The few times I used PicoDrive it sounded perfect, I don't think you have any business talking about it when you haven't used it in such a long time.

I understand. I was under the impression though that most of what Notaz did was speed things up and add support for new features like Mega CD support-- but I never heard about audio improvements.... correct me if I'm wrong.

I'd love to try a PC port if one exists and see how it sounds. For example Genesis Plus (which is derived from PicoDrive) has a PC version since it uses SDL. Thought it would be worth a shot to ask.... Last time I tried PicoDrive the audio was a good bit off.... the pitch was a bit off in some places, and some effects were just way out there. A really good test is the Ecco games.... especially Tides of Time where the dash sound and the sound of hitting a wall becomes a loud irritating screech ... the BG music is also unusually complex and it doesn't even sound right in Kega Fusion.

It's a good thing Genesis does have that Z80 or else I don't see how it'd do digital sound at all because it has no timers, which is not good at all. It needs a CPU to sit there and poll external variables while processing audio. If it had a timer IRQ then it wouldn't need a second CPU. I think Sega's solution to everything is "throw a CPU at it" (look at Saturn).. maybe there's some other technique for games that drive it with the 68k, I dunno.

I'm sure you know the Z80 is there for SMS compatibility.... attach the Power Base Converter and you can run SMS games on the MD courtesy of the SMS-compatible VDP, SMS-compatible audio generator and Z80. Also some custom sound engines can use the Z80 to amazing effects.... one guy I know wrote an engine that plays PCM using the Z80 and DAC at over 90 KHz! Sounds better than PCM in any other MD game I've played.....

Looking at Saturn I get the impression they had 3 groups working on different systems and lumped them together at the last minute..... like one making a 2D game console, one making a 3D game console, and one making an audio CD/MPEG video CD player.... Sega's very weird like that.

The difference is probably caused by the GP2x's shitty as hell speakers.

I always used headphones.... decent ones too.... although the 2x liked to turn its speakers back on whenever it felt like it .... :rolleyes:

 

[kfuse]

QUOTE
Looking at Saturn I get the impression they had 3 groups working on different systems and lumped them together at the last minute..... like one making a 2D game console, one making a 3D game console, and one making an audio CD/MPEG video CD player.... Sega's very weird like that.


wasn't just those. Don't forget the sega cdx... man I wish I still had one of those. It could play legit cd's and act as a walkman. even though majority of people didn't like the system that much.

 

[Exophase]

I'm sure you know the Z80 is there for SMS compatibility.... attach the Power Base Converter and you can run SMS games on the MD courtesy of the SMS-compatible VDP, SMS-compatible audio generator and Z80. Also some custom sound engines can use the Z80 to amazing effects.... one guy I know wrote an engine that plays PCM using the Z80 and DAC at over 90 KHz! Sounds better than PCM in any other MD game I've played.....

The z80 is there for sound, backwards compatibility is just an extra perk. Few games don't use it for sound, and if you use the DAC w/o the z80 you're basically adding a ton of complexity and extra CPU time since you have time slice all your algorithms to fit within a few hundred cycles per iteration. If Genesis didn't have the z80 I bet we'd be seeing a lot fewer games with DAC output.

 

[Exophase]

I was gone for a few days but I didn't miss anything so that's good. For those people who might be interested..

I'm going to start working on ARM code (and getting my emulator on GP2X properly) once basic compatibility is 90+%. I'm getting there, shouldn't be that much longer. Basic compatibility means that the game starts and you can play it for a few minutes and nothing goes wrong, I can't really test more than that.

 

[slaanesh]

I'm interested.

 

[DaveC]

I am interested too, thanks for doing this

 

[Rivroner]

Very happy to read this

 

[halo9]

I can't really test more than that.

That's what we're here for. Keep us posted!

 

[StealthBagel]

Glad to hear that, Exophase. The real benefit of this new handheld should be to make 8 and 16-bit console emulation dramatically more accurate and improve on the experience with better controls/screen/battery life.... that is more important to me than novelties like PSX emulation that some people are so worked up about. A lot of systems like Turbografx/PC engine and SNES are yet to be emulated with decent compatibility and accuracy on a handheld, and even NES emulation is lacking in a lot of areas (most notably speed last time I checked....)

I hope other emulator authors will work to redouble their previous efforts within the capabilities of this new hardware..

 

[Exophase]

Glad to hear that, Exophase. The real benefit of this new handheld should be to make 8 and 16-bit console emulation dramatically more accurate and improve on the experience with better controls/screen/battery life.... that is more important to me than novelties like PSX emulation that some people are so worked up about. A lot of systems like Turbografx/PC engine and SNES are yet to be emulated with decent compatibility and accuracy on a handheld, and even NES emulation is lacking in a lot of areas (most notably speed last time I checked....)

I hope other emulator authors will work to redouble their previous efforts within the capabilities of this new hardware..

I'm not trying to do a super accurate emulator, it's important that it runs very well on GP2X. Fortunately I think you have an exaggerated idea of what's necessary for accuracy in emulation. Usually it doesn't cost much more, although there will usually be a few games that require such a thing.

I am trying to get as many games working correctly as I can but PC-Engine games can be really finicky. Some of what I'm doing is a hack on a kludge on a hack. GBA was a much more ideal platform to emulate than this... I doubt I'll get super amazing compatibility but when the new handheld rolls around someone can just port Ootake or Mednafen (hell, that'd give you like 5 good emulators all at once).

What's so inaccurate about SNES emulation on handhelds anyway? I haven't heard about it myself but I thought it was more that it was slow under certain conditions (which is entirely expected), not inaccurate.

And I really doubt that NES emulation is slow, that goes against everything I've heard on the matter as well, and I just can't see how people would put up with that this long. Are you sure you aren't imagining this, or are you just very, very out of date?

 

[slaanesh]

Glad to hear that, Exophase. The real benefit of this new handheld should be to make 8 and 16-bit console emulation dramatically more accurate and improve on the experience with better controls/screen/battery life....

And I really doubt that NES emulation is slow, that goes against everything I've heard on the matter as well, and I just can't see how people would put up with that this long. Are you sure you aren't imagining this, or are you just very, very out of date?


GPFCE is a brilliant emulator for the NES and is IMHO very accurate. One of the few handheld NES emus that can run Elite correctly. I have had no problem running anything that I throw at it though I have tried Castlevania III which is supposed to be finicky?

One of the most amazing PC Engine emulators I know of is PCEAdvance - PC Engine for the GBA! It's really amazing considering the host system. I know that it makes use of GBA capabilites using native character mode and sprites so there's a big saving in terms of video rendering as the hardware takes care of most of this.

@ Exophase: Are you including CD emulation?