Subject: Re: FPU for a Shark
To: Ignatios Souvatzis <ignatios@cs.uni-bonn.de>
From: Richard Earnshaw <rearnsha@arm.com>
List: port-arm32
Date: 05/22/2000 10:45:10
> On Mon, May 22, 2000 at 07:18:02AM +0000, Matthias Scheler wrote:
> 
> > is it possible to equip a Shark with a FPU? It is how do I do it and what FPU
> > do I need?
> 
> No, not really*).

Indeed :-(

> 
> The StrongARM (which would be ARM"10") (like all higher-performance ARM

Eh?  StrongARM (strictly, SA-110) and ARM10 are completely different...

> variants)  does not have the coprocessor bus on external pins, so you can't
> connect the FPA10 hardware to it. Besides, I guess a Strongarm doing
> softfloat calls is faster than the old ARM FPU ;-)

Actually, no.  I believe that ARM7500FE based machines can still out-gun a 
strongarm for heavy FP-based apps.

> 
> I think the last ARM core which had an external coprocessor bus was
> ARM6 (maybe and ARM7?)

ARM6 and ARM7 are just cores, not chips.  All cores have a co-processor 
interface.  The chips with that interface brought out to pins were the 
ARM600 and ARM700.

> *) Of course, you have those two PCI and VLB on strange connector
> connectors...  you could design something that connects there, which is
> accessed as peripheral, and write a specialized compiler that uses
> them, or make the kernel trap for FP instructions and let the kernel
> use the hardware to execute them...
> 
> But I guess that is not what you're prepared to do...

RISC PC users running RISC OS on an ARM6/7 based machine could get some 
software that would make use of an x86 in the second processor slot to do 
FP calculations.  This gave a reasonable performance improvement for them. 
 It isn't worth while for StrongARM though, because of the overhead of 
syncing to the remote CPU.

R.