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.\" $OpenBSD: ahc.4,v 1.16 2001/06/22 12:15:43 mpech Exp $
.\" $NetBSD: ahc.4,v 1.1.2.1 1996/08/25 17:22:14 thorpej Exp $
.\"
.\" Copyright (c) 1995, 1996
.\" Justin T. Gibbs. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\"
.Dd March 20, 2000
.Dt AHC 4
.Os
.Sh NAME
.Nm ahc
.Nd Adaptec VL/EISA/PCI SCSI host adapter driver
.Sh SYNOPSIS
.ie 0 \{
For one or more VL/EISA cards:
.Cd controller eisa0
.Cd controller ahc0
\}
\{For VL cards:
.Cd ahc0 at isa? port ? irq ?
.Pp
For EISA cards:
.Cd ahc* at eisa? slot ?\}
.Pp
.ie 0 \{
For one or more PCI cards:
.Cd controller pci0
.Cd controller ahc0
\}
\{For PCI cards:
.Cd ahc* at pci? dev ? function ?\}
.Pp
.ie 0 \{
For one or more SCSI busses:
.Cd controller scbus0 at ahc0
\}
\{For SCSI busses:
.Cd scsibus* at ahc?\}
.Sh DESCRIPTION
This driver provides access to the
.Tn SCSI
bus(es) connected to Adaptec
.Tn AIC7770,
.Tn AIC7850,
.Tn AIC7860,
.Tn AIC7870,
.Tn AIC7880,
.Tn AIC7890,
.Tn AIC7891,
.Tn AIC7895,
.Tn AIC7896,
.Tn AIC7892,
.Tn AIC7897,
or
.Tn AIC7899
host adapter chips.
These chips are found on many motherboards as well as the following
Adaptec SCSI controller cards:
.Tn 274X(W),
.Tn 274X(T),
.Tn 284X,
.Tn 2920C,
.Tn 2930U2,
.Tn 2930CU,
.Tn 2940,
.Tn 2940U,
.Tn 2940AU,
.Tn 2940UW,
.Tn 2940UW Dual,
.Tn 2940U2W,
.Tn 2940U2B,
.Tn 2950U2W,
.Tn 2950U2B,
.Tn 29160,
.Tn 3940,
.Tn 3940U,
.Tn 3940AU,
.Tn 3940UW,
.Tn 3940AUW,
.Tn 3940U2W,
.Tn 3950U2,
and
.Tn 3985.
.Pp
Driver features include support for twin and wide busses,
fast, ultra and ultra2 synchronous transfers depending on controller type,
tagged queuing, and SCB paging.
.Pp
Memory mapped I/O can be enabled for PCI devices with the
.Dq Dv 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 fails to properly initialize the chip for memory mapped I/O.
The symptom of this problem is usually a system hang if memory mapped I/O
is attempted.
Most modern motherboards perform the initialization correctly and work fine
with this option enabled.
.Pp
Per target configuration performed in the
.Tn SCSI-Select
menu, accessible at boot
in
.No non- Ns Tn EISA
models,
or through an
.Tn EISA
configuration utility for
.Tn EISA
models,
is honored by this driver with the stipulation that the
.Tn BIOS
must be enabled for
.Tn EISA
adaptors.
This includes synchronous/asynchronous transfers, maximum synchronous
negotiation rate, disconnection, the host adapter's SCSI ID, and,
in the case of
.Tn EISA
Twin Channel controllers, the primary channel selection.
.Pp
Performance and feature sets vary throughout the aic7xxx product line.
The following table provides a comparison of the different chips
supported by the
.Nm
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.
.Pp
.Bd -filled -offset indent
.Bl -column "aic7770 " "10 " "EISA/VL " "10MHz " "16bit " "SCBs " Features
.Em "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
aic7891 20 PCI/64 40MHz 16Bit 16 3 4 5 6 7
aic7895 15 PCI/32 20MHz 16Bit 16 2 3 4 5
aic7896 20 PCI/32 40MHz 16Bit 16 2 3 4 5 6 7
aic7897 20 PCI/64 40MHz 16Bit 16 2 3 4 5 6 7
.El
.Pp
.Bl -enum -compact
.It
Multiplexed Twin Channel Device - One controller servicing two busses.
.It
Multi-function Twin Channel Device - Two controllers on one chip.
.It
Command Channel Secondary DMA Engine - Allows scatter gather list and
SCB prefetch.
.It
64 Byte SCB Support - SCSI CDB is embedded in the SCB to eliminate an extra DMA.
.It
Block Move Instruction Support - Doubles the speed of certain sequencer
operations.
.It
.Sq Bayonet
style Scatter Gather Engine - Improves S/G prefetch performance.
.It
Queuing Registers - Allows queuing of new transactions without pausing the
sequencer.
.El
.Ed
.Sh SCSI CONTROL BLOCKS (SCBs)
Every transaction sent to a device on the SCSI bus is assigned a
.Sq 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 have external SRAM.
.Pp
If external SRAM is not available, SCBs are a limited resource and
using them in a straight forward manner would only allow us to
keep as many transactions as there are SCBs outstanding at a time.
This would not allow enough concurrency to fully utilize the SCSI
bus and its devices.
The solution to this problem is
.Em 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.
.Sh SEE ALSO
.Xr aha 4 ,
.Xr ahb 4
.Sh AUTHORS
The
.Nm
driver, the
.Tn AIC7xxx
sequencer-code assembler, and the firmware running on the aic7xxx chips
were written by
.An Justin T. Gibbs .
.Sh BUGS
Some Quantum drives (at least the Empire 2100 and 1080s) will not run on an
.Tn 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
.Tn SCSI-Select
utility will allow normal operation.
|
