The
ahc device driver supports SCSI controllers based on Adaptec AIC77xx and AIC78xx SCSI host adapter chips found on many motherboards as well as Adaptec SCSI controller cards.
Driver features include support for twin and wide buses, fast, ultra or ultra2 synchronous transfers depending on controller type, tagged queuing and SCB paging.
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.
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/asynchronous 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 routines, but care should be taken when using a 284x (VESA local bus controller) in an EISA system. The jumpers setting the I/O area for the 284x should match the EISA slot into which the card is inserted to prevent conflicts with other EISA cards.
Performance and feature sets vary throughout the aic7xxx product line. The following table provides a comparison of the different chips supported by the
ahc driver. Note that wide and twin channel features, although always supported by a particular chip, may be disabled in a particular 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 buses.
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 eliminate 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 queuing of new transactions without pausing the sequencer.
8.
Multiple Target IDs - Allows the controller to respond to selection as a target on multiple SCSI IDs.