Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!rutgers!apple!vsi1!daver!lynx!m5
From: m5@lynx.uucp (Mike McNally)
Newsgroups: comp.unix.i386,comp.sys.intel
Subject: FPP initialization
Summary: Confusion, confusion, confusion
Message-ID: <5504@lynx.UUCP>
Date: 26 Apr 89 23:16:41 GMT
Reply-To: m5@lynx.UUCP (Mike McNally)
Distribution: na
Organization: Lynx Real-Time Systems Inc, Campbell CA
Lines: 47

I'm in some serious confusion over detection and initialization of a
floating point coprocessor in 386 AT compatibles.  So many things
confuse me that this message may prove very difficult to compose.

FIRST QUESTION:

What does your typical BIOS or setup program do when it "configures"
the floating point processor type (i.e., 287 or 387)?  Why does it
need to do this at all; the 386 is supposed to be able to figure that out
automatically!  Does it ignore the initial value of ET in CR0 and set
it to whatever it's told?

SECOND QUESTION:

What are the ramifications of using the FPP when ET is incorrect?  Like,
let's say I want to start from scratch after BIOS has done whatever
damage it thought appropriate.  I'd like to do something like this:

	Turn ET on, so we make believe we've got a 387
	Do an FNINIT
	Check the status and control words
	If the words are ugly, change ET and try again

OK, fine.  Of course, it doesn't work; at some point, after the whole
process completes, the initialization sequence does a WAIT and hangs.
Attempts to clear any errors via the magic OUT to F0 don't seem to
work.  In any case, the FNSTSW and FNSTCW seem to work regardless of
the state of ET.  The sequence finds nice status and control words on
my 287 and 387 machines with ET=1.

THIRD QUESTION:

What in the heck could a PC do to completely disable a coprocessor?  I've
got an NEC PowerMate 386 box with a 387 in it.  I can't find a setup
program, so I figure "well, I'll just hit on the FPP anyway."  No dice.
It's as if it's not even there.  I strongly suspect that AST machines
have a similar deal.  (Most of the machines I use are from Mylex.)


Anybody who has any experience with this stuff will receive my gratitude
for any pearls of wisdom.  

-- 
Mike McNally                                    Lynx Real-Time Systems
uucp: {voder,athsys}!lynx!m5                    phone: 408 370 2233

            Where equal mind and contest equal, go.