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 $
27 .\" $DragonFly: src/share/man/man4/scsi.4,v 1.4 2007/12/21 00:14:58 pavalos Exp $
34 .Nd CAM SCSI subsystem
37 .Cd "device scbus1 at ahc0"
38 .Cd "device scbus3 at ahc1 bus 0"
39 .Cd "device scbus2 at ahc1 bus 1"
46 .Cd "device ch1 at scbus0 target 4 unit 0"
47 .Cd "options CAMDEBUG"
48 .Cd "options CAM_DEBUG_BUS=-1"
49 .Cd "options CAM_DEBUG_TARGET=-1"
50 .Cd "options CAM_DEBUG_LUN=-1"
51 .Cd "options CAM_DEBUG_FLAGS=CAM_DEBUG_INFO|CAM_DEBUG_CDB"
52 .Cd "options CAM_MAX_HIGHPOWER=4"
53 .Cd "options CAM_NEW_TRAN_CODE"
54 .Cd "options SCSI_NO_SENSE_STRINGS"
55 .Cd "options SCSI_NO_OP_STRINGS"
56 .Cd "options SCSI_DELAY=8000"
60 subsystem provides a uniform and modular system for the implementation
61 of drivers to control various
63 devices, and to utilize different
65 host adapters through host adapter drivers.
66 When the system probes the
68 busses, it attaches any devices it finds to the appropriate
71 driver, if it is configured in the kernel, will attach to all
74 .Sh KERNEL CONFIGURATION
75 There are a number of generic kernel configuration options for the
79 .Bl -tag -width SCSI_NO_SENSE_STRINGS
81 This option enables the CAM debugging printf code. This won't actually
82 cause any debugging information to be printed out when included by itself.
83 Enabling printouts requires additional configuration. See below for
85 .It Dv "CAM_MAX_HIGHPOWER=4"
86 This sets the maximum allowable number of concurrent "high power" commands.
87 A "high power" command is a command that takes more electrical power than
88 most to complete. An example of this (and the only command currently
89 tagged as "high power") is the
91 START UNIT command. Starting a SCSI disk often takes significantly more
92 electrical power than normal operation of the disk. This option allows the
93 user to specify how many concurrent high power commands may be outstanding
94 without overloading the power supply on his computer.
95 .It Dv CAM_NEW_TRAN_CODE
96 This is a new transport layer code for CAM.
97 .It Dv SCSI_NO_SENSE_STRINGS
98 This eliminates text descriptions of each
100 Additional Sense Code and Additional Sense Code Qualifier pair. Since this
101 is a fairly large text database, eliminating it reduces the size of the
102 kernel somewhat. This is primarily necessary for boot floppies and other
103 low disk space or low memory space environments. In most cases, though,
104 this should be enabled, since it speeds the interpretation of
106 error messages. Don't let the "kernel bloat" zealots get to you -- leave
107 the sense descriptions in your kernel!
108 .It Dv SCSI_NO_OP_STRINGS
109 This disables text descriptions of each
111 opcode. This option, like the sense string option above, is primarily
112 useful for environments like a boot floppy where kernel size is critical.
113 Enabling this option for normal use isn't recommended, since it slows
117 .It Dv SCSI_DELAY=8000
120 "bus settle delay." In CAM, it is specified in
122 not seconds like the old
124 layer used to do. When the kernel boots, it sends a bus reset to each
126 bus to tell each device to reset itself to a default set of transfer
127 negotiations and other settings. Most
129 devices need some amount of time to recover from a bus reset. Newer disks
130 may need as little as 100ms, while old, slow devices may need much longer.
133 isn't specified, it defaults to 2 seconds. The minimum allowable value for
135 is "100", or 100ms. One special case is that if the
137 is set to 0, that will be taken to mean the "lowest possible value." In
140 will be reset to 100ms.
143 All devices and the SCSI busses support boot time allocation so that
144 an upper number of devices and controllers does not need to be configured;
146 will suffice for any number of disk drivers.
148 The devices are either
150 so they appear as a particular device unit or
152 so that they appear as the next available unused unit.
154 To configure a driver in the kernel without wiring down the device use a
155 config line similar to
157 to include the changer driver.
159 To wire down a unit use a config line similar to
160 .Cd "device ch1 at scbus0 target 4 unit 0"
161 to assign changer 1 as the changer with SCSI ID 4,
162 SCSI logical unit 0 on SCSI bus 0.
163 Individual scbuses can be wired down to specific controllers with
164 a config line similar to
165 .Cd "device scbus0 at ahc0"
166 which assigns scsi bus 0 to the first unit using the ahc driver.
167 For controllers supporting more than one bus,
168 the particular bus can be specified as in
169 .Cd "device scbus3 at ahc1 bus 1"
170 which assigns scbus 1 to the second bus probed on the ahc1 device.
172 When you have a mixture of wired down and counted devices then the
173 counting begins with the first non-wired down unit for a particular
174 type. That is, if you have a disk wired down as
176 then the first non-wired disk shall come on line as
179 The system allows common device drivers to work through many different
181 The adapters take requests from the upper layers and do
185 The maximum size of a transfer is governed by the
187 Most adapters can transfer 64KB in a single operation, however
188 many can transfer larger amounts.
190 Some adapters support
192 in which the system is capable of operating as a device, responding to
193 operations initiated by another system.
194 Target mode is supported for
195 some adapters, but is not yet complete for this version of the CAM
199 see other scsi device entries.
201 When the kernel is compiled with
202 .Cd "options CAMDEBUG" ,
203 an XPT_DEBUG CCB can be
204 used to enable various amounts of tracing information on any
206 Devices not being traced will not produce trace information.
207 There are currently four debugging flags that may be turned on:
208 .Bl -tag -width CAM_DEBUG_SUBTRACE
209 .It Dv CAM_DEBUG_INFO
210 This debugging flag enables general informational printfs for the device
211 or devices in question.
212 .It Dv CAM_DEBUG_TRACE
213 This debugging flag enables function-level command flow tracing. i.e.\&
214 kernel printfs will happen at the entrance and exit of various functions.
215 .It Dv CAM_DEBUG_SUBTRACE
216 This debugging flag enables debugging output internal to various functions.
218 This debugging flag will cause the kernel to print out all
220 commands sent to a particular device or devices.
223 Some of these flags, most notably
226 .Dv CAM_DEBUG_SUBTRACE
227 will produce kernel printfs in EXTREME numbers. Because of that, they
228 aren't especially useful. There aren't many things logged at the
230 level, so it isn't especially useful. The most useful debugging flag is
233 flag. Users can enable debugging from their kernel config file, by using
234 the following kernel config options:
235 .Bl -tag -width CAM_DEBUG_TARGET
237 This enables CAM debugging. Without this option, users will not even be able
238 to turn on debugging from userland via
240 .It Dv CAM_DEBUG_FLAGS
241 This allows the user to set the various debugging flags described above
242 in a kernel config file. Flags may be ORed together if the user wishes to
243 see printfs for multiple debugging levels.
245 Specify a bus to debug. To debug all busses, set this to -1.
246 .It Dv CAM_DEBUG_TARGET
247 Specify a target to debug. To debug all targets, set this to -1.
249 Specify a lun to debug. To debug all luns, set this to -1.
252 When specifying a bus, target or lun to debug, you
254 specify all three bus/target/lun options above. Using wildcards, you
255 should be able to enable debugging on most anything.
257 Users may also enable debugging printfs on the fly, if the
259 option is their config file, by using the
280 subsystem first appeared in
286 subsystem was written by