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Submitted by: Wilko Bulte, <wilko@yedi.iaf.nl>
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John Fieber
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2020-12-20 02:59:44 +00:00
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@ -1,11 +1,11 @@
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<!-- $Id: scsi.sgml,v 1.2 1995/06/30 17:37:48 jfieber Exp $ -->
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<!-- $Id: scsi.sgml,v 1.3 1995/08/29 01:42:45 jfieber Exp $ -->
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<!-- The FreeBSD Documentation Project -->
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<!--
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<title>An introduction to SCSI and its use with FreeBSD</title>
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<author>(c) 1995, Wilko Bulte, <tt/wilko@yedi.iaf.nl/
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<date>V0.2, Thu Apr 20 22:45:23 MET DST 1995</date>
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Copyright 1995, W. C. Bulte, Arnhem, The Netherlands
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<date>Sun Sep 3 17:14:48 MET DST 1995</date>
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Copyright 1995, Wilko C. Bulte, Arnhem, The Netherlands
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<abstract>
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This document attempts to describe the background of SCSI, its
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@ -15,7 +15,7 @@
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-->
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<sect><heading>SCSI<label id="scsi"></heading>
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<p><em>© 1995, &a.wilko;.</em>
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<p><em>© 1995, &a.wilko;.<newline>3 September 1995.</em>
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SCSI is an acronym for Small Computer Systems Interface. It is an
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ANSI standard that has become one of the leading I/O buses in the
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@ -38,7 +38,7 @@
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includes the (revised) CCS as part of the standard itself. The
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commands are dependent on the type of device at hand. It does not
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make much sense of course to define a Write command for a
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scanner...
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scanner.
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The SCSI bus is a parallel bus, which comes in a number of
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variants. The oldest and most used is an 8 bit wide bus, with
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@ -87,10 +87,10 @@
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QIC tape unit, a SCSI-1 helical scan tape unit and 2 SCSI-1 disks
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work together quite happily.
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<sect1><heading>Concepts of SCSI</heading>
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<sect1><heading>Components of SCSI</heading>
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<p>
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<sect2><heading>A <it>smart</it> interface</heading>
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<p>
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<!-- <sect2><heading>A <it>smart</it> interface</heading>
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<p> -->
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As said before, SCSI devices are smart. The idea is to put the
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knowledge about intimate hardware details onto the SCSI device
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itself. In this way, the host system does not have to worry
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@ -104,8 +104,8 @@
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there is no longer a need to change (and qualify!) drivers for
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every odd new device that is introduced.
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<sect2><heading>Do's and don't's on interconnections</heading>
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<p>
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<!-- <sect2><heading>Do's and don't's on interconnections</heading>
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<p> -->
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For cabling and connectors there is a golden rule: get good
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stuff. With bus speeds going up all the time you will save
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yourself a lot of grief by using good material.
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@ -116,9 +116,10 @@
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hunting down a problem with a flaky machine only to discover that
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shortening the SCSI bus with 1 meter solved the problem. And the
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original bus length was well within the SCSI specification.
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<sect2><heading>SCSI bus types</heading>
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<p>
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From an electrical point of view, there are two Incompatible bus
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From an electrical point of view, there are two incompatible bus
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types: single-ended and differential. This means that there are
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two different main groups of SCSI devices and controllers, which
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cannot be mixed on the same bus. It is possible however to use
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@ -148,7 +149,7 @@
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that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead
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of 5 Mbytes/sec for 'slow' SCSI. More on this later.
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It should be noted that the datalines > 8 are only used for
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It should be noted that the datalines > 8 are only used for
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datatransfers and device addressing. The transfers of commands
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and status messages etc are only performed on the lowest 8
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datalines. The standard allows narrow devices to operate on
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@ -216,7 +217,7 @@
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AH1740 as a single ended board, whereas the AH1744 was differential.
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The software interface to the host is identical for both.
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<sect3><heading>Terminators</heading>
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<sect2><heading>Terminators</heading>
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<p>
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Terminators in SCSI terminology are resistor networks that are
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used to get a correct impedance matching. Impedance matching
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@ -277,7 +278,7 @@
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for the internal flat cable connectors. This makes
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reconfiguration much easier.
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<sect3><heading>Terminator power</heading>
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<sect2><heading>Terminator power</heading>
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<p>
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The terminators discussed in the previous chapter need power to
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operate properly. On the SCSI bus, a line is dedicated to this
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@ -317,7 +318,7 @@
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configurable, using some sort of setup tool. Consult you
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documentation!
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<sect3><heading>Device addressing</heading>
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<sect2><heading>Device addressing</heading>
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<p>
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Because the SCSI bus is, ehh, a bus there must be a way to
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distinguish or address the different devices connected to it.
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@ -349,7 +350,7 @@
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tapechanger. In this way, the host system can address each of
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the parts of the tape unit as desired.
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<sect3><heading>Bus layout</heading>
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<sect2><heading>Bus layout</heading>
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<p>
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SCSI buses are linear. So, not shaped like Y-junctions, star
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topologies, cobwebbs or whatever else people might want to
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@ -366,7 +367,7 @@
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<sect1><heading>Using SCSI with FreeBSD</heading>
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<p>
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<sect2><heading>About translations, BIOSes and magic..</heading>
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<sect2><heading>About translations, BIOSes and magic...</heading>
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<p>
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As stated before, you should first make sure that you have a
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electrically sound bus.
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@ -447,8 +448,8 @@ Feb 9 19:33:46 yedi /386bsd: sd0: 636MB (1303250 total sec), 1632 cyl, 15 head,
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<sect2><heading>SCSI subsystem design</heading>
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<p>
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FreeBSD uses a sort of layered SCSI subsystem. For each different
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controller card a so called device driver is written. This driver
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FreeBSD uses a layered SCSI subsystem. For each different
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controller card a device driver is written. This driver
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knows all the intimate details about the hardware it
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controls. The driver has a interface to the upper layers of the
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SCSI subsystem through which it receives it's commands and
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@ -468,17 +469,95 @@ Feb 9 19:33:46 yedi /386bsd: sd0: 636MB (1303250 total sec), 1632 cyl, 15 head,
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<sect2><heading>Kernel configuration</heading>
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<p>
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Dependent on your hardware, the kernel configuration file must
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contain a line which describes your hostadapter. This includes
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I/O addresses, interrupts etc. Consult the man page for your
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adapter driver to get more info.
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contain one or more lines describing your hostadapter(s).
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This includes I/O addresses, interrupts etc.
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Consult the man page for your
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adapter driver to get more info. Apart from that, check out
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/sys/i386/conf/LINT for an overview of a kernel config file.
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LINT contains every possible option you can dream of. It
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does <em>not</em> imply LINT will actually get you to a
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working kernel at all.
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Although it is probably an obvious remark: the kernel config
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Although it is probably stating the obvious: the kernel config
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file should reflect your actual hardware setup. So, interrupts,
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I/O addresses etc must match the kernel config file.
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I/O addresses etc must match the kernel config file. During
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system boot messages will be displayed to indicate whether
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the configured hardware was actually found.
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An example from the kernel config file (they live in
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<tt>/sys/i386/conf</tt> BTW), with some added comments (between
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[]):
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An example based on the FreeBSD 2.0.5-Release kernel config
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file LINT with some added comments (between []):
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<verb>
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# SCSI host adapters: `aha', `ahb', `aic', `bt', `nca'
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#
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# aha: Adaptec 154x
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# ahb: Adaptec 174x
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# ahc: Adaptec 274x/284x/294x
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# aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!)
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# bt: Most Buslogic controllers
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# nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130
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# uha: UltraStore 14F and 34F
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# sea: Seagate ST01/02 8 bit controller (slow!)
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# wds: Western Digital WD7000 controller (no scatter/gather!).
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#
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# Note that the order is important in order for Buslogic cards to be
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# probed correctly.
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#
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[For a Bustek controller]
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controller bt0 at isa? port "IO_BT0" bio irq ? vector btintr
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[For an Adaptec AHA274x, 284x etc controller]
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controller ahc0 at isa? bio irq ? vector ahcintr # port??? iomem?
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[For an Adaptec AHA174x controller]
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controller ahb0 at isa? bio irq ? vector ahbintr
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[For an Adaptec AHA154x controller]
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controller aha0 at isa? port "IO_AHA0" bio irq ? drq 5 vector ahaintr
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[For an Ultrastor adapter]
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controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr
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controller scbus0 #base SCSI code
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disk sd0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0]
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disk sd1 at scbus0 target 1 [implicit LUN 0 if omitted]
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disk sd2 at scbus0 target 3
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disk sd3 at scbus0 target 4
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tape st1 at scbus0 target 6 [SCSI tape at target 6]
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device cd0 at scbus? [the first ever CDROM found, no wiring]
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</verb>
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The example above tells the kernel to look for a bt (Bustek)
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controller, then for an Adaptec 274x, 284x etc board, and
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so on. The lines following the controller specifications
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tell the kernel to configure specific devices but
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<em>only</em> attach them when they match the target ID and
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LUN specified.
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So, if you had a SCSI tape at target ID 2 it would not be
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configured, but it will attach when it is at target ID 6.
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Below is another example of a kernel config file as used by
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FreeBSD version < 2.0.5. The difference with the first example is
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that devices are not 'wired down'. 'Wired down' means
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that you specify which SCSI target belongs to which device.
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A kernel built to the config file below will attach
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the first SCSI disk it finds to sd0, the second disk to sd1
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etc. If you ever removed or added a disk, all other devices
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of the same type (disk in this case) would 'move around'.
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This implies you have to change /etc/fstab each time.
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Although the old style still works, you
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are <em>strongly</em> recommended to use this new feature.
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It will save you a lot of grief whenever you shift your
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hardware around on the SCSI buses. So, when you re-use
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your old trusty config file after upgrading from a
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pre-FreeBSD2.0.5.R system check this out.
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<verb>
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controller ahb0 at isa? bio irq 11 vector ahbintr [driver for Adaptec 174x]
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@ -498,11 +577,7 @@ device st1
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device cd0 #Only need one of these, the code dynamically grows [for the cdrom]
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</verb>
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So, the ahb driver is used for the Adaptec 1740, the aha driver
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for the Adaptec 154x etc. If you have more than one card of the
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same type in your system you get an ahb1, ahb2 line etc.
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The example above supports 4 SCSI disks. If during boot more
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Both examples support 4 SCSI disks. If during boot more
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devices of a specific type (e.g. sd disks) are found than are
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configured in the booting kernel, the system will complain. You
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will have to build and boot a new kernel (after adapting the kernel
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@ -644,44 +719,46 @@ options "TUNE_1542" #dynamic tune of bus DMA speed
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BBS (719-574-0424) and on the ncrinfo.ncr.com anonymous ftp site.
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Latest X3T10 committee documents are:
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<verb>
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AT Attachment (ATA or IDE) [X3.221-1994] Approved
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ATA Extensions (ATA-2) [X3T10/948D Rev 2i]
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Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] Approved
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Small Computer System Interface - 2 (SCSI-2) [X3.131-1994] Approved
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SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM)
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<itemize>
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<item>AT Attachment (ATA or IDE) [X3.221-1994] (<em>Approved</em>)
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<item>ATA Extensions (ATA-2) [X3T10/948D Rev 2i]
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<item>Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] (<em>Approved</em>)
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<item>Small Computer System Interface - 2 (SCSI-2) [X3.131-1994] (<em>Approved</em>)
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<item>SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM)
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[X3T10/792D Rev 11]
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</verb>
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</itemize>
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Other publications that might provide you with additional information are:
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<verb>
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"SCSI: Understanding the Small Computer System Interface", written by NCR
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<itemize>
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<item>"SCSI: Understanding the Small Computer System Interface", written by NCR
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Corporation. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632
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Phone: (201) 767-5937 ISBN 0-13-796855-8
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"Basics of SCSI", a SCSI tutorial written by Ancot Corporation
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<item>"Basics of SCSI", a SCSI tutorial written by Ancot Corporation
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Contact Ancot for availability information at:
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Phone: (415) 322-5322 Fax: (415) 322-0455
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"SCSI Interconnection Guide Book", an AMP publication (dated 4/93, Catalog
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<item>"SCSI Interconnection Guide Book", an AMP publication (dated 4/93, Catalog
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65237) that lists the various SCSI connectors and suggests cabling schemes.
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Available from AMP at (800) 522-6752 or (717) 564-0100
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"Fast Track to SCSI", A Product Guide written by Fujitsu.
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<item>"Fast Track to SCSI", A Product Guide written by Fujitsu.
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Available from: Prentice Hall, Englewood Cliffs, NJ, 07632
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Phone: (201) 767-5937 ISBN 0-13-307000-X
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"The SCSI Bench Reference", "The SCSI Encyclopedia", and the "SCSI Tutor",
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<item>"The SCSI Bench Reference", "The SCSI Encyclopedia", and the "SCSI Tutor",
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ENDL Publications, 14426 Black Walnut Court, Saratoga CA, 95070
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Phone: (408) 867-6642
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"Zadian SCSI Navigator" (quick ref. book) and "Discover the Power of SCSI"
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<item>"Zadian SCSI Navigator" (quick ref. book) and "Discover the Power of SCSI"
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(First book along with a one-hour video and tutorial book), Zadian Software,
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Suite 214, 1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800
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</verb>
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</itemize>
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On Usenet the newsgroups comp.periphs.scsi and comp.periphs are
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noteworthy places to look for more info. You can also find the
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SCSI-Faq there, which posted periodically.
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On Usenet the newsgroups <htmlurl
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url="news:comp.periphs.scsi" name="comp.periphs.scsi">
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and <htmlurl url="news:comp.periphs" name="comp.periphs">
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are noteworthy places to look for more info. You can also
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find the SCSI-Faq there, which is posted periodically.
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Most major SCSI device and hostadapter suppliers operate ftp sites
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and/or BBS systems. They may be valuable sources of information
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