Best CPU and FPU settings

[Bloodwych]

I've always wondered which are the best CPU and FPU options to choose for best compatibility, since speed in emulation is a mute point (ie an emulated 020 can be faster than a 060).

Leaving aside JIT disabled and Cycle Exact enabled, which out of the CPU/FPUs is the best combination? Just want to know the best CPU and FPU settings to use in my ClassicWB UAE pack configurations.

I'd imagine it's either of the following as the fastest and most complete/compatible:

68020+68881
or
68020+68882

Also is it worth setting the more compatible options under CPU and FPU? Does it fix much and how much of a speed penalty does it incure?

[Toni Wilen]

68020+6888x (1 or 2, only difference is FPU version byte in stack frame)

CPU more compatible = prefetch emulation, not much difference in 68020+ modes. Required in 68000 mode to handle self-modifying code (but today it is usually better to use cycle-exact mode) Don't remember what the FPU option does..

68020 is also good idea if you plan to use cycle-exact mode, 68030+ and cycle-exact is is even more approximate (and slower due to more complex caches) than 68020 CE.

In my opinion the best choice is to have 68020+6888x in JIT mode and have script (if non-whd game) or executestartup/cleanup (if whd) to switch JIT (and possibly cycle-exact) on/off on the fly when running hd-installed games or dems. Very fast WB but still compatible with most non-system friendly programs.

[Bloodwych]

Very useful info Toni, much appreciated thank you.

I agree the executestartup/cleanup option is excellent, as is the in-Workbench control, and more people should be made aware of it and set their games accordingly in WinUAE.

[Bloodwych]

Oh yeah and another thing -

Does pushing the CHIPRAM setting above 2MB real Amiga limit break anything in terms of compatibility?
Any disadvantage to using Z3 fast over normal 8MB fast?

If not I might as well give the configs 4/8MB CHIPRAM.

EDIT: Found this quote from you Toni so I'll assume it doesn't break any compatibility in comparision to 2MB:

8M is supported because it is easy to do and it is still very compatible.

More than 8M requires extra code. DMA emulation uses only one memory "bank" (it has to emulate wraparound and aliasing correctly), >8M requires two banks. "Normal" chip ram at address zero and extra bank in Z3 space. In other words: it requires extra code in low level emulation that should not be there in the first place Can do done but this is not good enough reason, at least not now..

[Toni Wilen]

Does pushing the CHIPRAM setting above 2MB real Amiga limit break anything in terms of compatibility?

I don't think so. (Of course there can be exceptions but they most likely already break if chip RAM size is >512K )

Any disadvantage to using Z3 fast over normal 8MB fast?

I think the only possible disadvantage is 32-bit CPU requirement (68EC020 or older won't work)

btw, your quote is obsolete because >8M Chip RAM is already implemented

[Bloodwych]

I never noticed that about the 8MB - you work wonders Mr Wilen.

[Bloodwych]

Originally Posted by Toni Wilen

to switch JIT (and possibly cycle-exact) on/off on the fly when running hd-installed games or dems. Very fast WB but still compatible with most non-system friendly programs.

Do you know the command to switch on cycle exact?

I tried:

uae-configuration cycle_exact true

What line would be the most compatible using uae-configuration before running games? WHDLoad has this set in its startup file:

uae-configuration cpu_speed real cachesize 0

[Toni Wilen]

Originally Posted by Bloodwych

Do you know the command to switch on cycle exact?

I tried:

uae-configuration cycle_exact true

I assume you had JIT enabled? You need to first disable JIT, set CPU speed setting and then set cycle-exact. (GUI does extra checks, directly changing config options does not check all possible conflicting options, there are too many..)

Something like: uae-confiugration cachesize 0 cpu_speed real cycle_exact true (and back on: cycle_exact false cpu_speed max cachesize 8192)

Hmm.. Maybe this system should support some kind of temporary variables so that it is possible to return back to real original settings.

What line would be the most compatible using uae-configuration before running games? WHDLoad has this set in its startup file:

uae-configuration cpu_speed real cachesize 0

This should be fine for most games. (Better disable JIT first and then set cpu speed. JIT without fastest possible is not exactly supported combination)

[Bloodwych]

Thanks Toni, just what I needed. Looking to use this in the ClassicWB UAE pack to better support WinUAE from within Workbench.