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     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:

     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 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
     2             host initiates PARTIAL PM state transition every time port
                   becomes idle;
     3             host initiates SLUMBER PM state transition every time port
                   becomes idle.
     4             driver initiates PARTIAL PM state transition 1ms after port
                   becomes idle;
     5             driver initiates SLUMBER PM state transition 125ms after
                   port becomes idle.
     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 is not compatible with device
     presence detection.  You will have to reset bus manually on device hot-

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


     This driver provides the CAM 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, hardware command queues (up to 32 commands per port), Native
     Command Queuing, SATA interface Power Management, device hot-plug and
     Message Signaled Interrupts.

     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.

     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).


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


     The ahci driver first appeared in FreeBSD 8.0.


     Alexander Motin 〈〉.