M68K for DC

[Stef]

[quote author=Clessy link=board=dcemu;num=1083323639;start=15#18 date=05/03/04 at 14:42:10]Not to be negitive but I dont see this going anywhere because hardly any coders actually know Sh4 ASM. Now even if you use the S4h book and look up string by string conversions you SH4 may be less optimized than the C core because it will most likly be sloppy if you're not use the the language.
[/quote]

I'm not a master of SH-4 assembly but i believe that it is quite simple to do a faster M68K core in SH-4 ASM than in C.
- First because a CPU emulator is really something where ASM will always keep a big advantage compared to C. For instance, emulating a ROR instruction with the correct flags need many C instructions where a few of ASM ones does the job...
Generally, just because of flags calculation stuff, ASM performs a lot better than C in CPU emulation.
- Second : the only SH-X C compiler we can use here is GCC, and unfortunatly it isn't the best C compiler for this CPU :-/ Generated code is somewhat a mess ... some values written in registers are never used later ...

IMO, a good knowledge of fast CPU emulation methods is more important than a good knowledge of SH-4 assembly

Also even once you have this core in asm we all know this isnt the end all solve all problem for coding. DreamSnes is the best example of this. Writing the core in ASM gave extremly lack luster speed ups compared to what they thought it would. Most of the processing power is killed in sound and video. This is a huge problem because you cant use the same video code for every emu without having to change some of the code correct? And if you have to change SH4 code wouldnt that make it so only about 3 of you would be able to use these cores as only 3 of you know a hand full od Sh4....

That's true, almost time video code is the bottle-neck.
But i don't think ASM can bring a big speed boost here compared to CPU emulation. Just have to optimise code and maybe use hardware acceleration where it's possible

BTW 600MB sound's exstordanily big for a simple core.....

I agree
I upgraded memory on my laptop just for that *:P

[Propeller]

I totally agree with Stef.

One of the "outputs" of this project is going to be a quick manual to SH4 newbies, in an effort to provide the scene with more people familiar to SH4 asm. It's a necessary condition that would eventually guarantee the quality of the results of the Dreamcast scene in the next couple of years.

Propeller

[DemoniusX]

I just want to comment on a couple things, I am all for this project, but I don't think
amiga 500 would work on DC, I mean with full speed and sound because the amiga (this and
commodore 64 are best of the 80's cpus IMO} is too complex, but I can see atari ST and maybe
MAYBE the Apple but I don't see that either, not to be negative but I for one would be up on
amiga like a woman *whistles* but I just don't think the DC can handle a perfect amiga emu
if so I will so be shocked :}

[Clessy]

Let's be serious here son the DC and play PSX games with super Ehanced graphics and you dont think it can handle a 80's pc....? I Sadly think your mistakin. Once everyone knows Sh4 your gonna see alot of kick ass emu support for DC game almost like a rebirth.

[wraggster]

Its only a matter of time until we many coders who know sh4asm like the back of their hand.

wouldnt it be fitting for the homebrew scene to release something thaat stuns the software world.

Just remember what the donkey kong country games did for the snes.

Its like having a car and tweaking it everywhere to squeeze the perfomance out of it.

One day we will see smoe amzing releases, the neogeo cd emu is one such release.

[DemoniusX]

ok, if fullspeed and sound amiga emulation happens of the DC, I will probably have a heart
attack, cuz what I wouldn't do to play risky woods on the DC, Ian micheal knows how much I
love the amiga, heh. I tried using the amiga emu called "winUAE" (sorry for being offtopic}
and I cannot get the fudging thing to work right, it sux. I hope the "rebirth" if it is a reality
happnens, to play "never thought possible" on dc, that would be definately a dream on DREAMcast
:}.

[Ian_micheal]

Hmm i think your forgeting how complex the amiga is here. Your have to have cycle perfect emulation it's more complex then a snes in some ways more then a psx. Im sorry to say i dont beleive it could be done at a playable speed. Just because it's a 80's pc means nothing.. SH4 asm is not going to totaly fix or help you port a very complex emu that uses lots of c++ kos does not support.

I can go throu in detail if you dont beleive me but amiga cant be underclocked or messed around with has to be perfect emulation. *I dont think you guys know how complex an amiga is compaired with an atari st. It has masses of custom hardware the amiga for video and sound and many cpu's much like the saturn.

[Stef]

[quote author=Ian_micheal link=board=dcemu;num=1083323639;start=15#26 date=05/05/04 at 06:05:09]Hmm i think your forgeting how complex the amiga is here. Your have to have cycle perfect emulation it's more complex then a snes in some ways more then a psx. Im sorry to say i dont beleive it could be done at a playable speed. Just because it's a 80's pc means nothing.. SH4 asm is not going to totaly fix or help you port a very complex emu that uses lots of c++ kos does not support.

I can go throu in detail if you dont beleive me but amiga cant be underclocked or messed around with has to be perfect emulation. *I dont think you guys know how complex an amiga is compaired with an atari st. It has masses of custom hardware the amiga for video and sound and many cpu's much like the saturn.[/quote]

Having CPU cycle emulation will improve a lot compatibility, but it's always possible to do a scanline based amiga emulator.
I think it's possible to have a full speed amiga emulator (without extras chips) with 80% software compatibility on Dreamcast... but is it really interesting to have a standalone amiga 500/600 emulator with only 80% compatibility rate ?
Remember Genecyst (a genesis emulator), Sardu made some choices, he volontary faked severals hardware features but then, he got about 85% of games playables at full speed with sound on a simple Pentium 100.
It was at this period the best choice

[Ian_micheal]

Beleive it when i see it Stef. But ive run a lot of tests doing that breaks almost 80% of games not the other way around still was not fullspeed or even close to it.


Much easyer to do a gba emu then this. Amiga you need cycle perfect emulation or all games break not just a few like the genesis.

[Stef]

Well i though that WinUAE used a dynarec for the M68K CPU, how it can do perfect cycle emulation with a dynarec ? and WinUAE does work at fullspeed on old machine (i speak about amiga 500 or 600)...

Anyway i don't know the amiga hardware much... so you're probably true.