.\" Copyright (c) 2009 Alexander Motin <mav@FreeBSD.org>
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.\" $FreeBSD$
.\"
.Dd June 26, 2009
.Dt AHCI 4
.Os
.Sh NAME
.Nm ahci
.Nd Serial ATA Advanced Host Controller Interface driver
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device pci"
.Cd "device scbus"
.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
.Pp
The following tunables are settable from the loader:
.Bl -ohang
.It Va hint.ahci.X.msi
controls Message Signaled Interrupts (MSI) usage by the specified controller
.Bl -tag -compact
.It 0
MSI disabled;
.It 1
single MSI vector used, if supported (default);
.It 2
multiple MSI vectors used, if supported;
.El
.It Va hint.ahcich.X.pm_level
controls SATA interface Power Management for specified channel,
allowing some power to be saved at the cost of additional command
latency.
Possible values:
.Bl -tag -compact
.It 0
interface Power Management is disabled (default);
.It 1
device is allowed to initiate PM state change, host is passive;
.It 2
host initiates PARTIAL PM state transition every time port becomes idle;
.It 3
host initiates SLUMBER PM state transition every time port becomes idle.
.El
Note that interface Power Management is not compatible with
device presence detection.
You will have to reset bus manually on device hot-plug.
.It Va hint.ahcich.X.sata_rev
setting to nonzero value limits maximum SATA revision (speed).
Values 1, 2 and 3 are respectively 1.5, 3 and 6Gbps.
.El
.Sh DESCRIPTION
This driver provides the CAM subsystem with native access to the
.Tn SATA
ports of AHCI-compatible controllers.
Each SATA port found is represented to CAM as a separate bus with one
target, or, if HBA supports Port Multipliers, 16 targets.
Most of the bus-management details are handled by the SATA-specific 
transport of CAM.
Connected ATA disks are handled by the ATA protocol disk peripheral driver
.Xr ada 4 .
ATAPI devices are handled by the SCSI protocol peripheral drivers
.Xr cd 4 ,
.Xr da 4 ,
.Xr sa 4 ,
etc.
.Pp
Driver features include support for Serial ATA and ATAPI devices,
Port Multipliers, hardware command queues (up to 32 commands per port),
Native Command Queuing, SATA interface Power Management, device hot-plug
and Message Signaled Interrupts.
.Pp
The Port Multiplier FIS Based Switching feature added in the AHCI 1.2
specification, which is required for effective parallel operation of devices
behind Port Multipliers, is not yet supported.
.Pp
AHCI hardware is also supported by ataahci driver from
.Xr ata 4
subsystem. If both drivers are loaded at the same time, this one will be
given precedence as the more functional of the two.
.Sh HARDWARE
The
.Nm
driver supports AHCI compatible controllers having PCI class 1 (mass storage),
subclass 6 (SATA) and programming interface 1 (AHCI).
.Sh SEE ALSO
.Xr ada 4 ,
.Xr cd 4 ,
.Xr da 4 ,
.Xr sa 4 ,
.Xr scsi 4 ,
.Xr ata 4
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 8.0 .
.Sh AUTHORS
.An Alexander Motin Aq mav@FreeBSD.org .