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 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 en

abled.

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 tar

get 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 syn

chronous/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 lo

cal 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 in

serted 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 dis

abled 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
busses.

2. Multi-function Twin Channel Device - Two con

trollers 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 trans

actions 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 2930U2
+o Adaptec 2940
+o Adaptec 2940J
+o Adaptec 2940N
+o Adaptec 2940U
+o Adaptec 2940AU
+o Adaptec 2940UW
+o Adaptec 2940UW Dual
+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 as

signed a `SCSI
Control Block' (SCB). The SCB contains all of the informa

tion required
by the controller to process a transaction. The chip fea

ture 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 re

source. 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 con

cept 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 transac

tions 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. Other

wise, 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 con

troller to queue
up to 255 transactions regardless of the amount of SCB

space. Since the
local SCB space serves as a cache for disconnected transac

tions, the more
SCB space available, the less host bus traffic consumed sav

ing 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 maxi

mum synchronous
negotiation rate of 8MHz in the SCSI-Select utility will al

low normal
operation.

Although the Ultra2 and Ultra160 products have sufficient

instruction ram
space to support both the initiator and target roles concur

rently, 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 avail

able from
Adaptec.

BSD July 4, 2004

BSD