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ahc(4)

NAME

     ahc -- Adaptec VL/EISA/PCI SCSI host adapter driver

SYNOPSIS

     For one or more VL/EISA cards:
     device eisa
     device ahc

     For one or more PCI cards:
     device pci
     device ahc

     To allow PCI adapters to use memory mapped I/O if enabled:
     options AHC_ALLOW_MEMIO

     To configure one or more controllers to assume the target role:
     options AHC_TMODE_ENABLE <bitmask of units>

     For one or more SCSI busses:
     device scbus

DESCRIPTION

     This driver provides access to the SCSI bus(es) connected to the Adaptec
     AIC77xx and AIC78xx host adapter chips.

     Driver features include support for twin and wide busses, fast, ultra or
     ultra2 synchronous transfers depending on controller type, tagged queue-
     ing, SCB paging, and target mode.

     Memory mapped I/O can be enabled for PCI devices with the
     ``AHC_ALLOW_MEMIO'' configuration option.	Memory mapped I/O is more
     efficient than the alternative, programmed I/O.  Most PCI BIOSes will map
     devices so that either technique for communicating with the card is
     available.  In some cases, usually when the PCI device is sitting behind
     a PCI->PCI bridge, the BIOS may fail to properly initialize the chip for
     memory mapped I/O.  The typical symptom of this problem is a system hang
     if memory mapped I/O is attempted.  Most modern motherboards perform the
     initialization correctly and work fine with this option enabled.

     Individual controllers may be configured to operate in the target role
     through the ``AHC_TMODE_ENABLE'' configuration option.  The value
     assigned to this option should be a bitmap of all units where target mode
     is desired.  For example, a value of 0x25, would enable target mode on
     units 0, 2, and 5.  A value of 0x8a enables it for units 1, 3, and 7.

     Per target configuration performed in the SCSI-Select menu, accessible at
     boot in non-EISA models, or through an EISA configuration utility for
     EISA models, is honored by this driver.  This includes synchronous/asyn-
     chronous transfers, maximum synchronous negotiation rate, wide transfers,
     disconnection, the host adapter's SCSI ID, and, in the case of EISA Twin
     Channel controllers, the primary channel selection.  For systems that
     store non-volatile settings in a system specific manner rather than a
     serial eeprom directly connected to the aic7xxx controller, the BIOS must
     be enabled for the driver to access this information.  This restriction
     applies to all EISA and many motherboard configurations.

     Note that I/O addresses are determined automatically by the probe rou-
     although always supported by a particular chip, may be disabled in a par-
     ticular motherboard or card design.

	   Chip       MIPS    Bus      MaxSync	 MaxWidth  SCBs  Features
	   aic7770     10    EISA/VL	10MHz	  16Bit     4	 1
	   aic7850     10    PCI/32	10MHz	   8Bit     3
	   aic7860     10    PCI/32	20MHz	   8Bit     3
	   aic7870     10    PCI/32	10MHz	  16Bit    16
	   aic7880     10    PCI/32	20MHz	  16Bit    16
	   aic7890     20    PCI/32	40MHz	  16Bit    16	     3 4 5 6 7 8
	   aic7891     20    PCI/64	40MHz	  16Bit    16	     3 4 5 6 7 8
	   aic7892     20    PCI/64	80MHz	  16Bit    16	     3 4 5 6 7 8
	   aic7895     15    PCI/32	20MHz	  16Bit    16	   2 3 4 5
	   aic7895C    15    PCI/32	20MHz	  16Bit    16	   2 3 4 5     8
	   aic7896     20    PCI/32	40MHz	  16Bit    16	   2 3 4 5 6 7 8
	   aic7897     20    PCI/64	40MHz	  16Bit    16	   2 3 4 5 6 7 8
	   aic7899     20    PCI/64	80MHz	  16Bit    16	   2 3 4 5 6 7 8

	   1.	Multiplexed Twin Channel Device - One controller servicing two
		busses.
	   2.	Multi-function Twin Channel Device - Two controllers on one
		chip.
	   3.	Command Channel Secondary DMA Engine - Allows scatter gather
		list and SCB prefetch.
	   4.	64 Byte SCB Support - SCSI CDB is embedded in the SCB to elim-
		inate an extra DMA.
	   5.	Block Move Instruction Support - Doubles the speed of certain
		sequencer operations.
	   6.	`Bayonet' style Scatter Gather Engine - Improves S/G prefetch
		performance.
	   7.	Queuing Registers - Allows queueing of new transactions with-
		out pausing the sequencer.
	   8.	Multiple Target IDs - Allows the controller to respond to
		selection as a target on multiple SCSI IDs.

HARDWARE

     The ahc driver supports the following SCSI host adapter chips and SCSI
     controller cards:

     o	 Adaptec AIC7770 host adapter chip
     o	 Adaptec AIC7850 host adapter chip
     o	 Adaptec AIC7860 host adapter chip
     o	 Adaptec AIC7870 host adapter chip
     o	 Adaptec AIC7880 host adapter chip
     o	 Adaptec AIC7890 host adapter chip
     o	 Adaptec AIC7891 host adapter chip
     o	 Adaptec AIC7892 host adapter chip
     o	 Adaptec AIC7895 host adapter chip
     o	 Adaptec AIC7896 host adapter chip
     o	 Adaptec AIC7897 host adapter chip
     o	 Adaptec AIC7899 host adapter chip
     o	 Adaptec 274X(W)
     o	 Adaptec 274X(T)
     o	 Adaptec 284X
     o	 Adaptec 2910
     o	 Adaptec 2915
     o	 Adaptec 2920
     o	 Adaptec 2930C
     o	 Adaptec 2940UW Pro
     o	 Adaptec 2940U2W
     o	 Adaptec 2940U2B
     o	 Adaptec 2950U2W
     o	 Adaptec 2950U2B
     o	 Adaptec 19160B
     o	 Adaptec 29160B
     o	 Adaptec 29160N
     o	 Adaptec 3940
     o	 Adaptec 3940U
     o	 Adaptec 3940AU
     o	 Adaptec 3940UW
     o	 Adaptec 3940AUW
     o	 Adaptec 3940U2W
     o	 Adaptec 3950U2
     o	 Adaptec 3960
     o	 Adaptec 39160
     o	 Adaptec 3985
     o	 Adaptec 4944UW
     o	 NEC PC-9821Xt13 (PC-98)
     o	 NEC RvII26 (PC-98)
     o	 NEC PC-9821X-B02L/B09 (PC-98)
     o	 NEC SV-98/2-B03 (PC-98)
     o	 Many motherboards with on-board SCSI support

SCSI CONTROL BLOCKS (SCBs)

     Every transaction sent to a device on the SCSI bus is assigned a `SCSI
     Control Block' (SCB).  The SCB contains all of the information required
     by the controller to process a transaction.  The chip feature table lists
     the number of SCBs that can be stored in on-chip memory.  All chips with
     model numbers greater than or equal to 7870 allow for the on chip SCB
     space to be augmented with external SRAM up to a maximum of 255 SCBs.
     Very few Adaptec controller configurations have external SRAM.

     If external SRAM is not available, SCBs are a limited resource.  Using
     the SCBs in a straight forward manner would only allow the driver to han-
     dle as many concurrent transactions as there are physical SCBs.  To fully
     utilize the SCSI bus and the devices on it, requires much more concur-
     rency.  The solution to this problem is SCB Paging, a concept similar to
     memory paging.  SCB paging takes advantage of the fact that devices usu-
     ally disconnect from the SCSI bus for long periods of time without talk-
     ing to the controller.  The SCBs for disconnected transactions are only
     of use to the controller when the transfer is resumed.  When the host
     queues another transaction for the controller to execute, the controller
     firmware will use a free SCB if one is available.	Otherwise, the state
     of the most recently disconnected (and therefore most likely to stay dis-
     connected) SCB is saved, via dma, to host memory, and the local SCB
     reused to start the new transaction.  This allows the controller to queue
     up to 255 transactions regardless of the amount of SCB space.  Since the
     local SCB space serves as a cache for disconnected transactions, the more
     SCB space available, the less host bus traffic consumed saving and
     restoring SCB data.

BUGS

     Some Quantum drives (at least the Empire 2100 and 1080s) will not run on
     an AIC7870 Rev B in synchronous mode at 10MHz.  Controllers with this
     problem have a 42 MHz clock crystal on them and run slightly above 10MHz.
     This confuses the drive and hangs the bus.  Setting a maximum synchronous

     Tagged Queuing is not supported in target mode.

     Reselection in target mode fails to function correctly on all high volt-
     age differential boards as shipped by Adaptec.  Information on how to
     modify HVD board to work correctly in target mode is available from
     Adaptec.

SEE ALSO

     aha(4), ahb(4), cd(4), da(4), sa(4), scsi(4)

AUTHORS

     The ahc driver, the AIC7xxx sequencer-code assembler, and the firmware
     running on the aic7xxx chips was written by Justin T. Gibbs.

HISTORY

     The ahc driver appeared in FreeBSD 2.0.

FreeBSD 5.4			 July 4, 2004			   FreeBSD 5.4

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