.\"	$OpenBSD: amdmsr.4,v 1.4 2008/06/19 11:33:08 mbalmer Exp $
.\"
.\" MSR access driver for AMD Geode LX CPUs with graphics processor.
.\" Copyright 2008 Marc Balmer <mbalmer@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
..\"
.Dd $Mdocdate: June 19 2008 $
.Dt AMDMSR 4 i386
.Os
.Sh NAME
.Nm amdmsr
.Nd access MSRs on certain AMD Geode LX systems
.Sh SYNOPSIS
.Cd "amdmsr0 at mainbus?"
.Sh DESCRIPTION
The
.Nm
device provides access to the Model Specific Registers (MSRs) on systems with
an AMD Geode LX CPU and graphics processor.
.Ss IOCTL INTERFACE
MSRs can be read or written via
.Fn ioctl
calls performed on
.Pa /dev/amdmsr .
Declarations and data types are to be found in
.Aq Pa machine/amdmsr.h .
.Pp
Read or write requests are performed using:
.Bd -literal -offset xxxx
struct amdmsr_req {
	u_int32_t addr;	/* 32-bit MSR address */
	u_int64_t val;	/* 64-bit MSR value */
};
.Ed
.Pp
The
.Fa RDMSR
ioctl is used to read an MSR register.
.Pp
The
.Fa WRMSR
ioctl is used to write an MSR register.
.Sh SEE ALSO
.Xr ioctl 2
.Sh HISTORY
.Nm
support was added in
.Ox 4.4 .