Subject: Re: 501-1105 FPA
To: Miod Vallat <>
From: Robert F Schaefer <>
List: port-sun3
Date: 01/09/2001 16:06:43
On Tue, 9 Jan 2001, Miod Vallat wrote:

>> > The ``Floating-Point Programmer's Guide for the Sun Workstation'' manua=
>> Know offhand where I might be able to get a hold of one? =20
>No. But I can xerox it and send it to you via snail mail, it's a bit
>more than 100 pages... hope Sun won't mind.

That would be great.

>> Hmmm.  PIO access to it?  Now I'm *really* interested in finding out
>> exactly what it does.  It would have to be fast at *something*, to be
>> worth going thru that much trouble for it!

>Basically it's designed to do fast matrix computation, and a few other
>operations useful for fortran programs. Every FPA instruction is a movel
>involving a memory address in the FPA mapping range. Given that the FPA
>can serve 32 different applications, there is likely to be some magic

Applications, as in concurrent processes?  I was wondering about that. 
I'm about 99 percent sure that it would be, uhhh, counterproductive to try
and save the FPA state during a context switch.  I would imagine it's the
drivers' responsibility to keep track of who gets what results.

>arithmetic involved in the mapping operation...
>Also, even weirder is the fact that, for ``regular'' floating point
>computation it doesn't handle, it sends FPE trap, to tell the system to
>dispatch this operation to the regular FPU ; that's why the FPA doesn't
>work at all if you don't have any FPU in your machine... and that
>enables an application compiled for FPA+ to work with the older FPA,
>with some speed penalty. This happen often because every computation
>which generates an ieee exception is aborted and passed back to the FPU,
>which does a better job at handling those.

Hmmm.  the FPU+ has an onboard '88[12]?

>Somewhat messy.
>> Would the _Programmers_ _Guide_ also have info about the other accelerato=
>> like the sky FFP, & FPA-2?
>Yes. But there isn't much on the sky, at least in my edition, as it was
>only supported on the Sun2s. Yet this is revision A, FCS, so I suppose
>there isn't much Sun official docs on the sky. The ``references''
>section mentions a ``Fast Floating-Point Processor Integration Manu=E6l''
>from Sky Computers which would probably fill the holes.

Ah.  How many FPA's (of whatever type) are there for the sun3 line?  FPA,
FPA+, FPA-2, some TI thing, any others?  Most likely, they would all
operate pretty much the same.