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Date: Wed, 17 Dec 1997 14:28:37 -0600 (CST)
From: Dave Bodenstab <imdave@mcs.net>
Message-Id: <199712172028.OAA18268@base486.home.org>
To: questions@FreeBSD.org
Subject: Cyrex floating point problem?
Sender: owner-freebsd-questions@FreeBSD.org
X-Loop: FreeBSD.org
Precedence: bulk


I've got a new pc (built from used parts) and it has a Cyrix cpu.
Everything is working (dos/windows/fbsd 2.2.5) with one glaring
problem.  When I run a floating point intensive program such as
povray, I get intermittent SIGFPE core dumps.  The same input,
the same program, etc. sometimes works, and other times core
dumps.  

If I just run pov and don't touch the machine until it finishes,
my success rate increases.

My guess is that there's some problem with context switching and
saving/restoring the FP state.  Or else there's some problem
handling masked FP exceptions...

Any ideas?

Here are snippets from the boot probes and kernel config:

/var/log/messages:
  Dec 17 02:09:20 base586 /kernel.new: Copyright (c) 1992-1997 FreeBSD Inc.
  Dec 17 02:09:20 base586 /kernel.new: Copyright (c) 1982, 1986, 1989, 1991, 1993
  Dec 17 02:09:20 base586 /kernel.new: 	The Regents of the University of California.  All rights reserved.
  Dec 17 02:09:20 base586 /kernel.new: 
  Dec 17 02:09:20 base586 /kernel.new: FreeBSD 2.2.5-RELEASE #4: Wed Dec 17 01:44:04 CST 1997
  Dec 17 02:09:20 base586 /kernel.new:     bin@base586.home.org:/usr/src/sys/compile/base586
  Dec 17 02:09:20 base586 /kernel.new: CPU: Cyrix 6x86 (486-class CPU)
  Dec 17 02:09:20 base586 /kernel.new:   Origin = "CyrixInstead"  DIR=0x1631  Stepping=1  Revision=6
  Dec 17 02:09:21 base586 /kernel.new:   CPU cache: write-through mode
  Dec 17 02:09:21 base586 /kernel.new: real memory  = 33554432 (32768K bytes)
  Dec 17 02:09:21 base586 /kernel.new: avail memory = 30474240 (29760K bytes)
  Dec 17 02:09:21 base586 /kernel.new: Probing for devices on PCI bus 0:
  Dec 17 02:09:21 base586 /kernel.new: chip0 <Intel 82437VX PCI cache memory controller> rev 2 on pci0:0
  Dec 17 02:09:21 base586 /kernel.new: chip1 <Intel 82371SB PCI-ISA bridge> rev 1 on pci0:7:0
  Dec 17 02:09:21 base586 /kernel.new: chip2 <Intel 82371SB IDE interface> rev 0 on pci0:7:1
  Dec 17 02:09:21 base586 /kernel.new: vga0 <VGA-compatible display device> rev 1 int a irq ?? on pci0:10
  Dec 17 02:09:21 base586 /kernel.new: Probing for devices on the ISA bus:
  Dec 17 02:09:22 base586 /kernel.new: npx0 on motherboard
  Dec 17 02:09:22 base586 /kernel.new: npx0: INT 16 interface

kernel config:
  machine	"i386"
  cpu		"I486_CPU"
  options	"AUTO_EOI_1"
  options	BOUNCE_BUFFERS
  device	npx0 at isa? port "IO_NPX" iosiz 0x0 flags 0x0 irq 13 vector npxintr


The comments in LINT about the npx flags imply that they do not apply
to me since I do not have "I586_CPU" as an option.

Dave Bodenstab
imdave@mcs.net