.\"	$OpenBSD: ahci.4,v 1.7 2008/04/19 01:18:39 djm Exp $
.\"
.\" Copyright (c) 2006 David Gwynne <dlg@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
.\" TORTIOUS ACTION, ARISING OUT OF
.\" PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd June 15, 2009
.Dt AHCI 4
.Os
.Sh NAME
.Nm ahci
.Nd Advanced Host Controller Interface for Serial ATA
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ahci"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ahci_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
driver provides support for Serial ATA controllers conforming to the
Advanced Host Controller Interface specification.
.Pp
Several AHCI capable controllers also provide a compatibility mode that
causes them to appear as a traditional ATA controller supported by
.Xr nata 4 .
.Pp
Although
.Nm
controllers are actual ATA controllers, the driver emulates SCSI via a
translation layer.
.Pp
Setting the lowest bit (0x1) of the driver flags forces
.Nm
to negotiate SATA 1 (1.5 Gb/s) transfer speeds only.
It may be useful where higher speeds are unstable.
.Sh SEE ALSO
.Xr intro 4 ,
.Xr nata 4 ,
.Xr pci 4 ,
.Xr scsi 4 ,
.Xr sili 4 ,
.Xr loader.conf 5
.Sh HISTORY
The
.Nm
driver first appeared in
.Dx 2.3 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was originally written by
.An David Gwynne Aq dlg@openbsd.org
and
.An Christopher Pascoe Aq pascoe@openbsd.org
for
.Ox .
.Pp
It was ported to
.Dx
by
.An Matt Dillon Aq dillon@apollo.backplane.com
who added new features such as port multiplier support.