ncr53c8xx.txt

linux 内核源代码

The Linux NCR53C8XX/SYM53C8XX drivers README file

Written by Gerard Roudier <[e-mail]>
21 Rue Carnot
95170 DEUIL LA BARRE - FRANCE

29 May 1999
===============================================================================

1.  Introduction
2.  Supported chips and SCSI features
3.  Advantages of the enhanced 896 driver
      3.1 Optimized SCSI SCRIPTS
      3.2 New features of the SYM53C896 (64 bit PCI dual LVD SCSI controller)
4.  Memory mapped I/O versus normal I/O
5.  Tagged command queueing
6.  Parity checking
7.  Profiling information
8.  Control commands
      8.1  Set minimum synchronous period
      8.2  Set wide size
      8.3  Set maximum number of concurrent tagged commands
      8.4  Set order type for tagged command
      8.5  Set debug mode
      8.6  Clear profile counters
      8.7  Set flag (no_disc)
      8.8  Set verbose level
      8.9  Reset all logical units of a target
      8.10 Abort all tasks of all logical units of a target
9.  Configuration parameters
10. Boot setup commands
      10.1 Syntax
      10.2 Available arguments
             10.2.1  Master parity checking
             10.2.2  Scsi parity checking
             10.2.3  Scsi disconnections
             10.2.4  Special features
             10.2.5  Ultra SCSI support
             10.2.6  Default number of tagged commands
             10.2.7  Default synchronous period factor
             10.2.8  Negotiate synchronous with all devices
             10.2.9  Verbosity level
             10.2.10 Debug mode
             10.2.11 Burst max
             10.2.12 LED support
             10.2.13 Max wide
             10.2.14 Differential mode
             10.2.15 IRQ mode
             10.2.16 Reverse probe
             10.2.17 Fix up PCI configuration space
             10.2.18 Serial NVRAM
             10.2.19 Check SCSI BUS 
             10.2.20 Exclude a host from being attached
             10.2.21 Suggest a default SCSI id for hosts
             10.2.22 Enable use of IMMEDIATE ARBITRATION
      10.3 Advised boot setup commands
      10.4 PCI configuration fix-up boot option
      10.5 Serial NVRAM support boot option
      10.6 SCSI BUS checking boot option
      10.7 IMMEDIATE ARBITRATION boot option
11. Some constants and flags of the ncr53c8xx.h header file
12. Installation
13. Architecture dependent features
14. Known problems
      14.1 Tagged commands with Iomega Jaz device
      14.2 Device names change when another controller is added
      14.3 Using only 8 bit devices with a WIDE SCSI controller.
      14.4 Possible data corruption during a Memory Write and Invalidate
      14.5 IRQ sharing problems
15. SCSI problem troubleshooting
      15.1 Problem tracking
      15.2 Understanding hardware error reports
16. Synchronous transfer negotiation tables
      16.1 Synchronous timings for 53C875 and 53C860 Ultra-SCSI controllers
      16.2 Synchronous timings for fast SCSI-2 53C8XX controllers
17. Serial NVRAM support (by Richard Waltham)
      17.1 Features
      17.2 Symbios NVRAM layout
      17.3 Tekram  NVRAM layout
18. Support for Big Endian
      18.1 Big Endian CPU
      18.2 NCR chip in Big Endian mode of operations

===============================================================================

1. Introduction

The initial Linux ncr53c8xx driver has been a port of the ncr driver from 
FreeBSD that has been achieved in November 1995 by:
          Gerard Roudier              <[e-mail]>

The original driver has been written for 386bsd and FreeBSD by:
          Wolfgang Stanglmeier        <[e-mail]>
          Stefan Esser                <[e-mail]>

It is now available as a bundle of 2 drivers:

- ncr53c8xx generic driver that supports all the SYM53C8XX family including 
  the earliest 810 rev. 1, the latest 896 (2 channel LVD SCSI controller) and
  the new 895A (1 channel LVD SCSI controller).
- sym53c8xx enhanced driver (a.k.a. 896 drivers) that drops support of oldest 
  chips in order to gain advantage of new features, as LOAD/STORE instructions 
  available since the 810A and hardware phase mismatch available with the 
  896 and the 895A.

You can find technical information about the NCR 8xx family in the
PCI-HOWTO written by Michael Will and in the SCSI-HOWTO written by
Drew Eckhardt.

Information about new chips is available at LSILOGIC web server:

          http://www.lsilogic.com/

SCSI standard documentations are available at SYMBIOS ftp server:

          ftp://ftp.symbios.com/

Useful SCSI tools written by Eric Youngdale are available at tsx-11:

          ftp://tsx-11.mit.edu/pub/linux/ALPHA/scsi/scsiinfo-X.Y.tar.gz
          ftp://tsx-11.mit.edu/pub/linux/ALPHA/scsi/scsidev-X.Y.tar.gz

These tools are not ALPHA but quite clean and work quite well.
It is essential you have the 'scsiinfo' package.

This short documentation describes the features of the generic and enhanced
drivers, configuration parameters and control commands available through 
the proc SCSI file system read / write operations.

This driver has been tested OK with linux/i386, Linux/Alpha and Linux/PPC.

Latest driver version and patches are available at:

          ftp://ftp.tux.org/pub/people/gerard-roudier
or
          ftp://ftp.symbios.com/mirror/ftp.tux.org/pub/tux/roudier/drivers

I am not a native speaker of English and there are probably lots of
mistakes in this README file. Any help will be welcome.


2. Supported chips and SCSI features

The following features are supported for all chips:

	Synchronous negotiation
	Disconnection
	Tagged command queuing
	SCSI parity checking
	Master parity checking

"Wide negotiation" is supported for chips that allow it.  The
following table shows some characteristics of NCR 8xx family chips 
and what drivers support them.

                                                  Supported by   Supported by
       On board                                   the generic    the enhanced 
Chip   SDMS BIOS   Wide   SCSI std.   Max. sync   driver         driver
----   ---------   ----   ---------   ----------  ------------   -------------
810        N         N      FAST10    10 MB/s        Y             N
810A       N         N      FAST10    10 MB/s        Y             Y
815        Y         N      FAST10    10 MB/s        Y             N
825        Y         Y      FAST10    20 MB/s        Y             N
825A       Y         Y      FAST10    20 MB/s        Y             Y
860        N         N      FAST20    20 MB/s        Y             Y
875        Y         Y      FAST20    40 MB/s        Y             Y
876        Y         Y      FAST20    40 MB/s        Y             Y
895        Y         Y      FAST40    80 MB/s        Y             Y
895A       Y         Y      FAST40    80 MB/s        Y             Y
896        Y         Y      FAST40    80 MB/s        Y             Y
897        Y         Y      FAST40    80 MB/s        Y             Y
1510D      Y         Y      FAST40    80 MB/s        Y             Y
1010       Y         Y      FAST80   160 MB/s        N             Y
1010_66*   Y         Y      FAST80   160 MB/s        N             Y

* Chip supports 33MHz and 66MHz PCI buses.


Summary of other supported features:

Module:                allow to load the driver
Memory mapped I/O:     increases performance
Profiling information: read operations from the proc SCSI file system
Control commands:      write operations to the proc SCSI file system
Debugging information: written to syslog (expert only)
Scatter / gather
Shared interrupt
Boot setup commands
Serial NVRAM:          Symbios and Tekram formats


3. Advantages of the enhanced 896 driver

3.1 Optimized SCSI SCRIPTS.

The 810A, 825A, 875, 895, 896 and 895A support new SCSI SCRIPTS instructions 
named LOAD and STORE that allow to move up to 1 DWORD from/to an IO register 
to/from memory much faster that the MOVE MEMORY instruction that is supported 
by the 53c7xx and 53c8xx family.
The LOAD/STORE instructions support absolute and DSA relative addressing 
modes.  The SCSI SCRIPTS had been entirely rewritten using LOAD/STORE instead 
of MOVE MEMORY instructions.

3.2 New features of the SYM53C896 (64 bit PCI dual LVD SCSI controller)

The 896 and the 895A allows handling of the phase mismatch context from 
SCRIPTS (avoids the phase mismatch interrupt that stops the SCSI processor 
until the C code has saved the context of the transfer).
Implementing this without using LOAD/STORE instructions would be painfull 
and I didn't even want to try it.

The 896 chip supports 64 bit PCI transactions and addressing, while the 
895A supports 32 bit PCI transactions and 64 bit addressing.
The SCRIPTS processor of these chips is not true 64 bit, but uses segment 
registers for bit 32-63. Another interesting feature is that LOAD/STORE 
instructions that address the on-chip RAM (8k) remain internal to the chip.

Due to the use of LOAD/STORE SCRIPTS instructions, this driver does not 
support the following chips:
- SYM53C810 revision < 0x10 (16)
- SYM53C815 all revisions
- SYM53C825 revision < 0x10 (16)

4. Memory mapped I/O versus normal I/O

Memory mapped I/O has less latency than normal I/O.  Since
linux-1.3.x, memory mapped I/O is used rather than normal I/O.  Memory
mapped I/O seems to work fine on most hardware configurations, but
some poorly designed motherboards may break this feature.

The configuration option CONFIG_SCSI_NCR53C8XX_IOMAPPED forces the
driver to use normal I/O in all cases.


5. Tagged command queueing

Queuing more than 1 command at a time to a device allows it to perform 
optimizations based on actual head positions and its mechanical 
characteristics. This feature may also reduce average command latency.
In order to really gain advantage of this feature, devices must have 
a reasonable cache size (No miracle is to be expected for a low-end 
hard disk with 128 KB or less).
Some kown SCSI devices do not properly support tagged command queuing.
Generally, firmware revisions that fix this kind of problems are available 
at respective vendor web/ftp sites.
All I can say is that the hard disks I use on my machines behave well with 
this driver with tagged command queuing enabled:

- IBM S12 0662
- Conner 1080S
- Quantum Atlas I
- Quantum Atlas II

If your controller has NVRAM, you can configure this feature per target 
from the user setup tool. The Tekram Setup program allows to tune the 
maximum number of queued commands up to 32. The Symbios Setup only allows 
to enable or disable this feature.

The maximum number of simultaneous tagged commands queued to a device
is currently set to 8 by default.  This value is suitable for most SCSI
disks.  With large SCSI disks (>= 2GB, cache >= 512KB, average seek time
<= 10 ms), using a larger value may give better performances.

The sym53c8xx driver supports up to 255 commands per device, and the 
generic ncr53c8xx driver supports up to 64, but using more than 32 is 
generally not worth-while, unless you are using a very large disk or disk 
array. It is noticeable that most of recent hard disks seem not to accept 
more than 64 simultaneous commands. So, using more than 64 queued commands 
is probably just resource wasting.

If your controller does not have NVRAM or if it is managed by the SDMS 
BIOS/SETUP, you can configure tagged queueing feature and device queue 
depths from the boot command-line. For example:

  ncr53c8xx=tags:4/t2t3q15-t4q7/t1u0q32

will set tagged commands queue depths as follow:

- target 2  all luns  on controller 0 --> 15
- target 3  all luns  on controller 0 --> 15
- target 4  all luns  on controller 0 -->  7
- target 1  lun 0     on controller 1 --> 32
- all other target/lun                -->  4

In some special conditions, some SCSI disk firmwares may return a
QUEUE FULL status for a SCSI command. This behaviour is managed by the
driver using the following heuristic:

- Each time a QUEUE FULL status is returned, tagged queue depth is reduced 
  to the actual number of disconnected commands. 

- Every 1000 successfully completed SCSI commands, if allowed by the
  current limit, the maximum number of queueable commands is incremented.

Since QUEUE FULL status reception and handling is resource wasting, the 
driver notifies by default this problem to user by indicating the actual 
number of commands used and their status, as well as its decision on the 
device queue depth change.
The heuristic used by the driver in handling QUEUE FULL ensures that the 
impact on performances is not too bad. You can get rid of the messages by 
setting verbose level to zero, as follow:

1st method: boot your system using 'ncr53c8xx=verb:0' option.
2nd method: apply "setverbose 0" control command to the proc fs entry 
            corresponding to your controller after boot-up.

6. Parity checking

The driver supports SCSI parity checking and PCI bus master parity
checking.  These features must be enabled in order to ensure safe data
transfers.  However, some flawed devices or mother boards will have
problems with parity. You can disable either PCI parity or SCSI parity 
checking by entering appropriate options from the boot command line.
(See 10: Boot setup commands).

7. Profiling information

Profiling information is available through the proc SCSI file system.
Since gathering profiling information may impact performances, this 
feature is disabled by default and requires a compilation configuration 
option to be set to Y.

The device associated with a host has the following pathname:

          /proc/scsi/ncr53c8xx/N     (N=0,1,2 ....)

Generally, only 1 board is used on hardware configuration, and that device is:
          /proc/scsi/ncr53c8xx/0

However, if the driver has been made as module, the number of the
hosts is incremented each time the driver is loaded.