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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 con-
     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 con-
     troller.  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 pas-
     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	pres-
     ence 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 repre-
     sented 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 Inter-

     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 88SX61xx.

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

     The ahci driver first appeared in FreeBSD 8.0.

     Alexander Motin <>.

FreeBSD	8.1		       January 28, 2010			   FreeBSD 8.1


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