2 .\" Julian Elischer <julian@FreeBSD.org>. All rights reserved.
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26 .\" $FreeBSD: src/share/man/man4/scsi.4,v 1.18.2.7 2001/08/17 13:08:39 ru Exp $
33 .Nd CAM SCSI subsystem
36 .Cd "device scbus1 at ahc0"
37 .Cd "device scbus3 at ahc1 bus 0"
38 .Cd "device scbus2 at ahc1 bus 1"
45 .Cd "device ch1 at scbus0 target 4 unit 0"
46 .Cd "options CAMDEBUG"
47 .Cd "options CAM_DEBUG_BUS=-1"
48 .Cd "options CAM_DEBUG_TARGET=-1"
49 .Cd "options CAM_DEBUG_LUN=-1"
50 .Cd "options CAM_DEBUG_FLAGS=CAM_DEBUG_INFO|CAM_DEBUG_CDB"
51 .Cd "options CAM_MAX_HIGHPOWER=4"
52 .Cd "options SCSI_NO_SENSE_STRINGS"
53 .Cd "options SCSI_NO_OP_STRINGS"
54 .Cd "options SCSI_DELAY=8000"
58 subsystem provides a uniform and modular system for the implementation
59 of drivers to control various
61 devices, and to utilize different
63 host adapters through host adapter drivers.
64 When the system probes the
66 busses, it attaches any devices it finds to the appropriate
69 driver, if it is configured in the kernel, will attach to all
72 .Sh KERNEL CONFIGURATION
73 There are a number of generic kernel configuration options for the
77 .Bl -tag -width SCSI_NO_SENSE_STRINGS
79 This option enables the CAM debugging printf code. This won't actually
80 cause any debugging information to be printed out when included by itself.
81 Enabling printouts requires additional configuration. See below for
83 .It Dv "CAM_MAX_HIGHPOWER=4"
84 This sets the maximum allowable number of concurrent "high power" commands.
85 A "high power" command is a command that takes more electrical power than
86 most to complete. An example of this (and the only command currently
87 tagged as "high power") is the
89 START UNIT command. Starting a SCSI disk often takes significantly more
90 electrical power than normal operation of the disk. This option allows the
91 user to specify how many concurrent high power commands may be outstanding
92 without overloading the power supply on his computer.
93 .It Dv SCSI_NO_SENSE_STRINGS
94 This eliminates text descriptions of each
96 Additional Sense Code and Additional Sense Code Qualifier pair. Since this
97 is a fairly large text database, eliminating it reduces the size of the
98 kernel somewhat. This is primarily necessary for boot floppies and other
99 low disk space or low memory space environments. In most cases, though,
100 this should be enabled, since it speeds the interpretation of
102 error messages. Don't let the "kernel bloat" zealots get to you -- leave
103 the sense descriptions in your kernel!
104 .It Dv SCSI_NO_OP_STRINGS
105 This disables text descriptions of each
107 opcode. This option, like the sense string option above, is primarily
108 useful for environments like a boot floppy where kernel size is critical.
109 Enabling this option for normal use isn't recommended, since it slows
113 .It Dv SCSI_DELAY=8000
116 "bus settle delay." In CAM, it is specified in
118 not seconds like the old
120 layer used to do. When the kernel boots, it sends a bus reset to each
122 bus to tell each device to reset itself to a default set of transfer
123 negotiations and other settings. Most
125 devices need some amount of time to recover from a bus reset. Newer disks
126 may need as little as 100ms, while old, slow devices may need much longer.
129 isn't specified, it defaults to 2 seconds. The minimum allowable value for
131 is "100", or 100ms. One special case is that if the
133 is set to 0, that will be taken to mean the "lowest possible value." In
136 will be reset to 100ms.
139 All devices and the SCSI busses support boot time allocation so that
140 an upper number of devices and controllers does not need to be configured;
142 will suffice for any number of disk drivers.
144 The devices are either
146 so they appear as a particular device unit or
148 so that they appear as the next available unused unit.
150 To configure a driver in the kernel without wiring down the device use a
151 config line similar to
153 to include the changer driver.
155 To wire down a unit use a config line similar to
156 .Cd "device ch1 at scbus0 target 4 unit 0"
157 to assign changer 1 as the changer with SCSI ID 4,
158 SCSI logical unit 0 on SCSI bus 0.
159 Individual scbuses can be wired down to specific controllers with
160 a config line similar to
161 .Cd "device scbus0 at ahc0"
162 which assigns scsi bus 0 to the first unit using the ahc driver.
163 For controllers supporting more than one bus,
164 the particular bus can be specified as in
165 .Cd "device scbus3 at ahc1 bus 1"
166 which assigns scbus 1 to the second bus probed on the ahc1 device.
168 When you have a mixture of wired down and counted devices then the
169 counting begins with the first non-wired down unit for a particular
170 type. That is, if you have a disk wired down as
172 then the first non-wired disk shall come on line as
175 The system allows common device drivers to work through many different
177 The adapters take requests from the upper layers and do
181 The maximum size of a transfer is governed by the
183 Most adapters can transfer 64KB in a single operation, however
184 many can transfer larger amounts.
186 Some adapters support
188 in which the system is capable of operating as a device, responding to
189 operations initiated by another system.
190 Target mode is supported for
191 some adapters, but is not yet complete for this version of the CAM
195 see other scsi device entries.
197 When the kernel is compiled with
198 .Cd "options CAMDEBUG" ,
199 an XPT_DEBUG CCB can be
200 used to enable various amounts of tracing information on any
202 Devices not being traced will not produce trace information.
203 There are currently four debugging flags that may be turned on:
204 .Bl -tag -width CAM_DEBUG_SUBTRACE
205 .It Dv CAM_DEBUG_INFO
206 This debugging flag enables general informational printfs for the device
207 or devices in question.
208 .It Dv CAM_DEBUG_TRACE
209 This debugging flag enables function-level command flow tracing. i.e.\&
210 kernel printfs will happen at the entrance and exit of various functions.
211 .It Dv CAM_DEBUG_SUBTRACE
212 This debugging flag enables debugging output internal to various functions.
214 This debugging flag will cause the kernel to print out all
216 commands sent to a particular device or devices.
219 Some of these flags, most notably
222 .Dv CAM_DEBUG_SUBTRACE
223 will produce kernel printfs in EXTREME numbers. Because of that, they
224 aren't especially useful. There aren't many things logged at the
226 level, so it isn't especially useful. The most useful debugging flag is
229 flag. Users can enable debugging from their kernel config file, by using
230 the following kernel config options:
231 .Bl -tag -width CAM_DEBUG_TARGET
233 This enables CAM debugging. Without this option, users will not even be able
234 to turn on debugging from userland via
236 .It Dv CAM_DEBUG_FLAGS
237 This allows the user to set the various debugging flags described above
238 in a kernel config file. Flags may be ORed together if the user wishes to
239 see printfs for multiple debugging levels.
241 Specify a bus to debug. To debug all busses, set this to -1.
242 .It Dv CAM_DEBUG_TARGET
243 Specify a target to debug. To debug all targets, set this to -1.
245 Specify a lun to debug. To debug all luns, set this to -1.
248 When specifying a bus, target or lun to debug, you
250 specify all three bus/target/lun options above. Using wildcards, you
251 should be able to enable debugging on most anything.
253 Users may also enable debugging printfs on the fly, if the
255 option is their config file, by using the
274 subsystem first appeared in
280 subsystem was written by