NAME¶
ahc
—
Adaptec VL/EISA/PCI SCSI host adapter driver
SYNOPSIS¶
To compile this driver into the kernel, place the following lines in your kernel
configuration file:
device scbus
device ahc
For one or more VL/EISA cards:
device eisa
For one or more PCI cards:
device pci
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>
Alternatively, to load the driver as a module at boot time, place the following
lines in
loader.conf(5):
ahc_load="YES"
ahc_eisa_load="YES"
ahc_isa_load="YES"
ahc_pci_load="YES"
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 queueing, 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/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 |
- Multiplexed Twin Channel Device - One controller servicing two
busses.
- Multi-function Twin Channel Device - Two controllers on one chip.
- Command Channel Secondary DMA Engine - Allows scatter gather list and SCB
prefetch.
- 64 Byte SCB Support - SCSI CDB is embedded in the SCB to eliminate an
extra DMA.
- Block Move Instruction Support - Doubles the speed of certain sequencer
operations.
- ‘Bayonet’ style Scatter Gather Engine - Improves S/G
prefetch performance.
- Queuing Registers - Allows queueing of new transactions without pausing
the sequencer.
- 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:
- Adaptec AIC7770 host adapter chip
- Adaptec AIC7850 host adapter chip
- Adaptec AIC7860 host adapter chip
- Adaptec AIC7870 host adapter chip
- Adaptec AIC7880 host adapter chip
- Adaptec AIC7890 host adapter chip
- Adaptec AIC7891 host adapter chip
- Adaptec AIC7892 host adapter chip
- Adaptec AIC7895 host adapter chip
- Adaptec AIC7896 host adapter chip
- Adaptec AIC7897 host adapter chip
- Adaptec AIC7899 host adapter chip
- Adaptec 274X(W)
- Adaptec 274X(T)
- Adaptec 284X
- Adaptec 2910
- Adaptec 2915
- Adaptec 2920C
- Adaptec 2930C
- Adaptec 2930U2
- Adaptec 2940
- Adaptec 2940J
- Adaptec 2940N
- Adaptec 2940U
- Adaptec 2940AU
- Adaptec 2940UW
- Adaptec 2940UW Dual
- Adaptec 2940UW Pro
- Adaptec 2940U2W
- Adaptec 2940U2B
- Adaptec 2950U2W
- Adaptec 2950U2B
- Adaptec 19160B
- Adaptec 29160B
- Adaptec 29160N
- Adaptec 3940
- Adaptec 3940U
- Adaptec 3940AU
- Adaptec 3940UW
- Adaptec 3940AUW
- Adaptec 3940U2W
- Adaptec 3950U2
- Adaptec 3960
- Adaptec 39160
- Adaptec 3985
- Adaptec 4944UW
- NEC PC-9821Xt13 (PC-98)
- NEC RvII26 (PC-98)
- NEC PC-9821X-B02L/B09 (PC-98)
- NEC SV-98/2-B03 (PC-98)
- 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 handle as many
concurrent transactions as there are physical SCBs. To fully utilize the SCSI
bus and the devices on it, requires much more concurrency. The solution to
this problem is
SCB Paging, a concept similar to
memory paging. SCB paging takes advantage of the fact that devices usually
disconnect from the SCSI bus for long periods of time without talking 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 disconnected) 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.
SEE ALSO¶
aha(4),
ahb(4),
cd(4),
da(4),
sa(4),
scsi(4)
HISTORY¶
The
ahc
driver appeared in
FreeBSD 2.0.
AUTHORS¶
The
ahc
driver, the AIC7xxx sequencer-code
assembler, and the firmware running on the aic7xxx chips was written by
Justin T. Gibbs.
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 negotiation rate of
8MHz in the SCSI-Select utility will allow normal operation.
Although the Ultra2 and Ultra160 products have sufficient instruction ram space
to support both the initiator and target roles concurrently, this
configuration is disabled in favor of allowing the target role to respond on
multiple target ids. A method for configuring dual role mode should be
provided.
Tagged Queuing is not supported in target mode.
Reselection in target mode fails to function correctly on all high voltage
differential boards as shipped by Adaptec. Information on how to modify HVD
board to work correctly in target mode is available from Adaptec.