.\"	$OpenBSD: npx.4,v 1.12 2003/07/28 20:09:13 jason Exp $
.\"
.\" Copyright (c) 1993 Christopher G. Demetriou
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.\"      This product includes software developed by Christopher G. Demetriou.
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.Dd August 6, 1993
.Dt NPX 4 i386
.Os
.Sh NAME
.Nm npx
.Nd Numeric Processing Extension coprocessor and emulator
.Sh SYNOPSIS
.Cd "option GPL_MATH_EMULATE"
.\" XXX this is awful hackery to get it to work right... -- cgd
.Cd "npx0 at isa? port" \&"IO_NPX0\&" irq 13
.Sh DESCRIPTION
The
.Nm
driver enables the use of the system's Numeric Processing Extension
coprocessor,
if one is present.
Numeric processing extensions are present in systems with
.Tn 486DX
CPUs and in systems with
.Tn 387
or
.Tn 487SX
coprocessors.
The
.Nm
driver is required for proper system functioning regardless
of whether or not a NPX is present.
.Pp
If there is no NPX present in the system
.Ic option GPL_MATH_EMULATE
must be defined in the kernel configuration file.
It will provide support for the instructions normally executed by the NPX.
If there is no NPX in the system and the kernel
is not built with math emulation, the system will not boot.
.Sh SEE ALSO
.Xr intro 4 ,
.Xr isa 4
.Sh CAVEATS
The emulator is much slower than the NPX coprocessor.
This will result in poor floating-point math performance
if the emulator must be used.
.Sh BUGS
There are lots of them, especially on cheap motherboards.
In particular, some motherboards do not have the interrupt lines from the NPX
to the CPU wired properly.
If this is the case, the emulator must be used if consistent system operation
is desired.
.Pp
Emulation of the transcendental functions instructions is incorrect.
Emulation of other instructions is suspect.