Re: [hatari-devel] 68040/68060, external FPU?

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 09/07/2025 à 12:29, Eero Tamminen a écrit :
> Hi,
>
> On 6.7.2025 18.13, Uwe Seimet wrote:
> > I noticed that Hatari accepts configuring an external FPU when using a
> > 68040/68060 processor. As far as I know neither 68040 nor 68060 
> > support an
> > external FPU.
>
> On quick googling I didn't find any definitive statement on that, but it 
> seems to be so.
>
> > Wouldn't it be better to reject such a configuration?
>
> Hatari cannot really reject it because there's no separate setting for 
> enabling FPU for 040/060 and selecting FPU type for 030.
>
> Because initial config values coming from config file, and user being 
> able to give CLI options in any order, it would be bad to reject:
>      --fpu internal --cpulevel 4
>      --fpu 68882 --cpulevel 3
> But accept:
>      --cpulevel 4 --fpu internal
>      --cpulevel 4 --fpu 68882
> Depending what was in config file, or earlier in command line.
>
> Changing config value for FPU type, once machine/CPU type is known, has 
> issues too, but maybe it would make sense to output a warning about it.
>
> What the warning says, would depend on whether WinUAE CPU core already 
> ignores non-internal FPU setting for 040/060 though.  I haven't checked.
>
> Nicolas?

Hi

it all depends if we speak of FPU as a logic part of the setup, ie sthg 
that can do floating point or as a real stand alone HW component.

In all cases, the cpu core from WinUAE can have the following values for 
fpu_model : 68881, 68882, 68040 and 68060.

and in M68000_CheckCpuSettings() we already warn if user chooses fpu 
internal for cpu <= 030.  Maybe a similar warning would be needed if 
user chooses fpu 68881/82 (ie not internal) on cpu >= 040.