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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


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

     controls Message Signaled Interrupts (MSI) usage by the specified controller
     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 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.  A
     manual bus reset is needed on device hot-plug.

     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(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), etc.

     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 Interrupts.

     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


     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


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


     The ahci driver first appeared in FreeBSD 8.0.


     Alexander Motin <>.