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AHCI(4)                FreeBSD Kernel Interfaces Manual                AHCI(4)

     ahci - Serial ATA Advanced Host Controller Interface driver

     To compile this driver into the kernel, place the following lines in your
     kernel configuration file:

           device pci
           device scbus
           device ahci

     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):


     The following tunables are settable from the loader(8):

     controls Message Signaled Interrupts (MSI) usage by the specified
     0   MSI disabled;
     1   single MSI vector used, if supported (default);
     2   multiple MSI vectors used, if supported;

     controls Command Completion Coalescing (CCC) usage by the specified
     controller.  Non-zero value enables CCC and defines maximum time (in ms),
     request can wait for interrupt, if there are some more requests present
     on controller queue.  CCC reduces number of context switches on systems
     with many parallel requests, but it can decrease disk performance on some
     workloads due to additional command latency.

     controls SATA interface Power Management for the specified channel,
     allowing some power to be saved at the cost of additional command
     latency.  Possible values:
     0   interface Power Management is disabled (default);
     1   device is allowed to initiate PM state change, host is passive;
     2   host initiates PARTIAL PM state transition every time port becomes
     3   host initiates SLUMBER PM state transition every time port becomes
     4   driver initiates PARTIAL PM state transition 1ms after port becomes
     5   driver initiates SLUMBER PM state transition 125ms after port becomes
     Some controllers, such as ICH8, do not implement modes 2 and 3 with NCQ
     used.  Because of artificial entering latency, performance degradation in
     modes 4 and 5 is much smaller then in modes 2 and 3.

     Note that interface Power Management complicates device presence
     detection.  A manual bus reset/rescan may be needed after device hot-
     plug, unless hardware implements Cold Presence Detection.

     setting to nonzero value limits maximum SATA revision (speed).  Values 1,
     2 and 3 are respectively 1.5, 3 and 6Gbps.

     setting to nonzero value forces driver attach to some known AHCI-capable
     chips even if they are configured for legacy IDE emulation.  Default is

     This driver provides the CAM(4) subsystem with native access to the 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 ada(4).  ATAPI devices
     are handled by the SCSI protocol peripheral drivers cd(4), da(4), sa(4),

     Driver features include support for Serial ATA and ATAPI devices, Port
     Multipliers (including FIS-based switching, when supported), hardware
     command queues (up to 32 commands per port), Native Command Queuing, SATA
     interface Power Management, device hot-plug and Message Signaled

     Driver supports "LED" enclosure management messages, defined by the AHCI.
     When supported by hardware, it allows to control per-port activity,
     locate and fault LEDs via the led(4) API for localization and status
     reporting purposes.  Supporting AHCI controllers may transmit that
     information to the backplane controllers via SGPIO interface. Backplane
     controllers interpret received statuses in some way (IBPI standard) to
     report them using present indicators.

     AHCI hardware is also supported by ataahci driver from 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.

     The ahci driver supports AHCI compatible controllers having PCI class 1
     (mass storage), subclass 6 (SATA) and programming interface 1 (AHCI).

     Also, in cooperation with atamarvell and atajmicron drivers of ata(4), it
     supports AHCI part of legacy-PATA + AHCI-SATA combined controllers, such
     as JMicron JMB36x and Marvell 88SE61xx.

     /dev/led/ahcich*.act     activity LED device nodes

     /dev/led/ahcich*.fault   fault LED device nodes

     /dev/led/ahcich*.locate  locate LED device nodes

     ada(4), ata(4), cam(4), cd(4), da(4), sa(4)

     The ahci driver first appeared in FreeBSD 8.0.

     Alexander Motin <>.

FreeBSD 11.0-PRERELEASE          June 18, 2012         FreeBSD 11.0-PRERELEASE


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