Re: [hatari-devel] Hatari FPU support

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 06/12/2020 à 21:42, Eero Tamminen a écrit :
> Hi,
>
> On 12/5/20 6:11 PM, Jerome Vernet wrote:
> > Wich CPU/FPU combination are usable ?
> >
> > Even thru the SDL GUI, I can select 68000/6882, Hatari ask to restart,
> > but no FPU is shown..
> >
> > There is now way to have a 6882 with a 68000 ?
>
> Hatari manual "The CPU Dialog" section says:
> "The FPU settings are also only available with
> the "WinUAE" builds of Hatari. They can be used
> to select the type of floating point unit of CPUs
>  >= 68020."
>
> Looking back to old discussions on 68000 FPU
> support, they apparently work very differently
> and would be hard to emulate & undocumented.
>
> See:
> * Thorsten: 
> https://listengine.tuxfamily.org/lists.tuxfamily.org/hatari-devel/2015/12/msg00008.html 
>
> * Toni: 
> https://listengine.tuxfamily.org/lists.tuxfamily.org/hatari-devel/2015/12/msg00007.html 
>
>
>
> Nicolas, I think FPU should be listed in Hatari
> manual HW matrix, but I'm not sure what notes
> I should add for each machine type.  Any suggestions?

Hi

FPU line could be added to the matrix. 68881/82 can be used with 
68020/030. With 68040/60, FPU is included in the cpu (but as these cpu 
were not natively used in atari's machine, it's not an issue for the HW 
matrix).

As christian wrote, 68000/10 can't use the 68881/82 directly ; note that 
Winuae's cpu core has a hack mode to use the FPU with 68000/10 anyway, 
but we don't use it in Hatari for now.

So, in the end, I think that FPU emulation should be marked as available 
i the matrix only for TT/Falcon (ie 68030 CPU). Other machines are using 
a 68000, so it should not be considered as possible (at least for Hatari 
at the moment, even if some HW modifications could be made, as described 
by Christian)

Nicolas

> SDL, macOS & Python GUI should probably also note
> that FPU selection is 020+ specific.
>
> (And I guess I should move FPU accuracy note from
> Features section to CPU dialog section.)
>
>
>      - Eero