freebsd-dev/share/man/man4/man4.i386/npx.4

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.\" Copyright (c) 1993 Christopher G. Demetriou
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.\"	from: npx.4,v 1.1 1993/08/06 10:58:03 cgd Exp
.\" $FreeBSD$
.\"
.Dd August 28, 1993
.Dt NPX 4 i386
.Os FreeBSD
.Sh NAME
.Nm npx
.Nd Numeric Processing Extension coprocessor and emulator
.Sh SYNOPSIS
.Cd "device npx0 at nexus? port IO_NPX flags 0x0 irq 13"
.Pp
For hosts without a FPU coprocessor add:
.Cd "options MATH_EMULATE"
or
.Cd "options GPL_MATH_EMULATE"
.\" XXX this is awful hackery to get it to work right... -- cgd
.\" What the heck does he mean? - cracauer
.Sh DESCRIPTION
The
.Nm npx
driver enables the use of the system's Numeric Processing Extension
coprocessor,
if one is present.  Numeric processing extensions are present in
systems with
.Sy 486DX
CPUs and in systems with
.Sy 387
or
.Sy 487SX
coprocessors.  The
.Nm npx
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, the MATH_EMULATE or
GPL_MATH_EMULATE option 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.
.Pp
You can choose to use a much more fully-featured math emulator (under the
GPL license) by including the option GPL_MATH_EMULATE in your kernel
configuration file instead of the MATH_EMULATE option.
.Pp
The
.Sy GENERIC
kernel configuration uses the MATH_EMULATE option.
.Pp
For a description of the possible "flags" values see the LINT kernel
configuration file.
.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.
.Pp
The non-GPL emulator does not support the whole set of npx
instructions.
It is sufficient for booting and configuring a system, but it cannot
support a system with normal workload unless care is taken to compile
the whole system (including third-party packages) with compiler
options that avoid the use of the non-emulated instructions.
.Sh BUGS
There are lots of them, especially on old 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
When using the default MATH_EMULATE option,
transcendental function instructions are not implemented.
Emulation of other instructions is suspect.