[hatari-devel] Long mail : new cpu cores + 2 questions.

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I've played around with the new winuae cores for the last days.

There are 6 cores available :

cpuemu_0 : a generic 68x00 cpu (used when no prefetch nor cycle exact config in the GUI), both for 68000 and 68030 emu
cpuemu_11 : same as before, but for prefetch mode and 68000 only
cpuemu_12 : this one is for the 68000 cycle exact mode only
cpuemu_20 : this one is for the 68020 emulation prefetch + cycle exact
cpuemu_21 : this one is for the 68030 emulation prefetch + cycle exact
cpuemu_31 : this one is for 68040 and 68060 emulation

Actually, I can let run quite correctly the following cores:
cpuemu_21 (I'll have to send a patch soon for this one)

2 cores are still not running :
cpuemu_12 (very strange code behing it)
cpu_emu31+MMU activated (TRY/CATCH/RETRY) to recode first

First : Core updating.
I've tried to upgrade the cores to latest winuae source, but I broke things.
There are few changes in the cores between the 2 versions, but patching must be done carefully.
I'll try it another time later.

ST emulation :

For ST emulation, the closest core to our actual oldcpu core are cpuemu_0 or cpuemu_11 (very close to each other, only prefetch differs).

If we want to retrieve the actual old cpu compatibility, we have 2 possibilities :

- using cpuemu_11 as the main 68000 core, and patch gencpu.c to rollback the different patchs Nicolas added there. For example, getDivs68kCycles and getDivu68kCycles are only called with cpuemu_12, so, we'll have to reintroduce them into gencpu.c

- let the cpuemu12 running (it may be harder, and I don't understand everything here).

I think we should only concentrate on 1 cpu and forget the others, as Nicolas has proved that the cpuemu11 can reach a good level in accuracy. I can do this job if you want to try to get as close as possible to the actual CPU ( I don't think it'll be that long and difficult, as we've got the old gencpu as example).

Falcon emulation :

2 cores are running :

cpuemu_0 : the generic 68000 core is used for 68030 and 68030 + prefetch emulation. It runs 68030 data and register caches and 68030 MMU code. the problem with this core is that is uses the 68000 cycles. I get the best results with this one actually (I run it with prefetch).

cpuemu_21 : the cycle exact core. I've got some results with it now, but it seems to be less accurate than the cpuemu_0 core. Some demo freeze with this one, but runs well with cpuemu_0. It's not completly "cycle exact", as for example the divs, divu and divl cycles are computed with the worst cycles value instead of the accurate value.
It let works 68030 caches and 68030 MMU too.

My suggest: for Hatari emulation, we could keep only 3 cores :

cpuemu_11 for ATARI 68000 core and repatch it to reach the actual level of compatibility. cpuemu_0 for FALCON emulation with a lot of changes in it (cycles, ...) to let it be closer to a 68030 or cpuemu_21 (but the code is much more complex and accuracy is lower for now).

We would only run hatari in accuracy mode for the ST, in best accuracy for the 68030 Falcon and generic accuracy 68060 for later. No more GUI with a lot of options like prefetch, ... (I don't think the speed difference is noteable with or without prefetch nowadays)
No more 68000 running with a MMU or a DSP.
We could only choose ST, ST, TT, FALCON (and later accelerated falcon) and choose the with/without copro or DSP.

Or we can continue to offer many parameters in the GUI and in the emulator, but 6 cores are a great effort to maintain and cpuemu_0 is used both for generic 68000 and Falcon, wich means a lot of "IF" to add everywhere in gencpu.c to keep accuracy for all cpus.

One day or the other, we'll have to make some choice with the new core and make some improvements and changes into it. If I keep it "compatible" with winuae without changing anything, falcon emu won't improve anymore.

But in the same time, I think I reach the limits of my knowledges here with Motorola CPU. Falcon gets quite well emulated, but there are still a lot of little problems here and there (accuracy, sound noise, ...) I think DSP is running quite well, everything is emulated. Crossbar is here too.
I lack of documentation (as I had for the DSP for example).
And I'm not such an expert of 68x00 processors.

I can patch the 68030 cycles according to motorola's docs (or better, Mikro's doc when he finished it) to help.
Maybe you could give me ideas of things to do in hatari to improve it.

Other point : videl emulation:

I've done some work with videl emu (I still have the code here on my hardisk). But separating video.c and videl.c implies huge changes I don't want to do lonely.
video.c in integrated everywhere in hatari (psg.c, mfp.c, ...)
It would be nice to have an interface to call in all parts of hatari that would run either with video.c or videl.c. I would have to reintegrate timer A, B, C, D, HBL, VBL into videl.c (I've already done some of them).

I don't want to add "if FALCON ..." everywhere in the code (as I've done into my actual code). It was easy to separate the sound (crossbar VS stedma sound), but video is too glued everywhere in ST mode.

Last point : cpu speed.

Is dividing the cycles by 2 (or 4) to let the 68000 run at 16 or 32 Mhz is the only way to do it ? My 68030 falcon should run natively at 16 Mhz (1 instruction cycles shoudn't be divided). I should have more cycles for each VBL, crossbar should run with the 68030 cycles (not divided by 2 nor 4), same for DSP.

Isn't there a "more beautiful" way to do the frequency emulation (keeping the cycles intact and having twice more cycles for each VBL for example).

Maybe this point is perfect and doesn't need any change, but it always "annoys" me to have the 68030 cycles divided by 2.

I stop here.
Thanks to read it to the end (and sorry for my approximate english)



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