config root man

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.\" Copyright (c) 1993 Christopher G. Demetriou
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.\"      This product includes software developed by Christopher G. Demetriou.
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.\"	$Id: npx.4,v 1.1 1993/08/06 10:58:03 cgd Exp $
.\" $FreeBSD: release/9.1.0/share/man/man4/man4.i386/npx.4 117871 2003-07-22 08:15:29Z peter $
.\"
.Dd August 28, 1993
.Dt NPX 4 i386
.Os
.Sh NAME
.Nm npx
.Nd Numeric Processing Extension coprocessor
.Sh SYNOPSIS
.Cd "device npx"
.Cd hint.npx.0.at="nexus"
.Cd hint.npx.0.port="0x0F0"
.Cd hint.npx.0.flags="0x0"
.Cd hint.npx.0.irq="13"
.Sh DESCRIPTION
The
.Nm
driver enables the use of the system's Numeric Processing Extension
coprocessor.
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.
If there is no NPX in the system, the system will not boot.
.Pp
The flags for
.Pa npx0
are:
.Pp
.Bl -tag -width indent -compact
.It 0x01
do not use the NPX registers to optimize bcopy.
.It 0x02
do not use the NPX registers to optimize bzero.
.It 0x04
do not use the NPX registers to optimize copyin or copyout.
.El
.Pp
The NPX registers are normally used
to optimize copying and zeroing
when all of the following conditions are satisfied:
.Pp
.Bl -enum -compact
.It
.Cd "cpu I586_CPU"
is an option
.It
the CPU is an i586 (perhaps not a Pentium)
.It
the probe for
.Pa npx0
succeeds
.It
INT 16 exception handling works.
.El
.Pp
Then copying and zeroing
using the NPX registers
is normally 30-100% faster.
.Pp
The flags can be used
to control cases
where it does not work or is slower.
Setting them at boot time
using userconfig works correctly
(the optimizations are not used
until later in the bootstrap
when
.Pa npx0
is attached).
.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.