Ubuntu Manpage: sane-scsi - SCSI adapter tips for scanners

NAME

       sane-scsi - SCSI adapter tips for scanners

DESCRIPTION

       This  manual page contains various operating-system specific tips and tricks on how to get
       scanners with a SCSI interface working.

GENERAL INFO

For scanners with a SCSI interface, it may be necessary to edit the appropriate backend
configuration file before using SANE for the first time. For most systems, the
configuration file should list the name of the generic SCSI device that the scanner is
connected to (e.g., under Linux, /dev/sg4 or /dev/sge is such a generic SCSI device). It
is customary to create a symlink from /dev/scanner to the generic SCSI device that the
scanner is connected to. In this case, the configuration file simply lists the line
/dev/scanner. For a detailed description of each backend's configuration file, please
refer to the relevant backend manual page (e.g., sane-epson(5) for Epson scanners,
sane-hp(5) for HP scanners, etc.).

For some operating systems (e.g. Linux and OS/2), there is an alternate way of specifying
scanner devices. This alternate way allows one to identify scanners by the SCSI vendor
and model string and/or by the SCSI device address (consisting of bus number, channel
number, id, and logical unit number). The syntax for specifying a scanner in this way is:

scsi VENDOR MODEL TYPE BUS CHANNEL ID LUN

where VENDOR is the SCSI vendor string, MODEL is the SCSI model string, TYPE is type SCSI
device type string, BUS is the SCSI bus number (named "host" in /proc/scsi/scsi), CHANNEL
is the SCSI channel number, ID is the SCSI id, and LUN is the logical unit number of the
scanner device. The first two fields are strings which must be enclosed in double-quotes
if they contain any whitespace. The remaining four fields are non-negative integer
numbers. The correct values for these fields can be found by using operating system
specific tools, e.g. for Linux by looking at the output of the command cat
/proc/scsi/scsi. To simplify configuration, a field's value can be replaced with an
asterisk symbol (``*''). An asterisk has the effect that any value is allowed for that
particular field. This can have the effect that a single scsi-line matches multiple
devices. When this happens, each matching device will be probed by the backend one by one
and registered if the backend thinks it is a compatible device. For example, the line

scsi MUSTEK MFS-06000CX Scanner 0 00 03 00

would attach the Mustek SCSI scanner with the following /proc/scsi/scsi entry:

Host: scsi0 Channel: 00 Id: 03 Lun: 00
Vendor: MUSTEK Model: MFS-06000CX Rev: 4.04
Type: Scanner ANSI SCSI revision: 0

Usually it's sufficient to use vendor and model strings only or even only the vendor
string. The following example

scsi MUSTEK * * * * * *

would have the effect that all SCSI devices in the system with a vendor string of MUSTEK
would be probed and recognized by the backend.

If the remainder of a scsi-string consists of asterisks only, the asterisks can be
omitted. For example, the following line is equivalent to the one specified previously:

scsi MUSTEK

On some platforms (e.g., OpenStep), SANE device names take a special form. This is
explained below in the relevant platform-specific section.

When using a SCSI scanner, ensure that the access permission for the generic SCSI device
is set appropriately. We recommend to add a group "scanner" to /etc/group which contains
all users that should have access to the scanner. The permission of the device should
then be set to allow group read and write access. For example, if the scanner is at
generic SCSI device /dev/sg0, then the following two commands would set the permission
correctly:

$ chgrp scanner /dev/sg0
$ chmod 660 /dev/sg0

When your system uses the device filesystem (devfs), you have to edit /etc/devfs/perms.
There you should search the line

and add a new line (eg. for changing permissions of sg4):

FREEBSD INFO

       Auto-configuration using the "scsi *" lines in the config files only  works  if  the  user
       running the frontend has read/write access to /dev/xpt0.  Instead, you can also set a link
       /dev/scanner to the appropriate /dev/uk device.

              Adaptec AHA1542CF
                     Reported to work fine under FreeBSD 2.2.2R with the aha driver.

              Adaptec 2940
                     Reported to work fine under FreeBSD 2.2.2.

              Adaptec 1522
                     The scanner probes ok but any attempt to access it hangs the entire  system.
                     It  looks  like  something  is disabling interrupts and then not re-enabling
                     them, so it looks like a bug in the FreeBSD aic driver.

              Adaptec 1505
                     Works on FreeBSD 2.2.5R and 3.0 using the aic driver,  provided  that  Plug-
                     and-Play  support is disabled on the card.  If there are no uk devices, just
                     do a sh MAKEDEV uk0 in the  /dev  directory.  The  scanner  should  then  be
                     accessible as /dev/uk0 if it was probed during boot.

              Tekram DC390
                     Reported to work fine under FreeBSD 2.2.2R with the amd driver.

LINUX INFO

First, make sure your kernel has SCSI generic support enabled. In make xconfig, this
shows up under ``SCSI support->SCSI generic support''.

To keep scanning times to a minimum, it is strongly recommended to use a large buffer size
for the generic SCSI driver. From SG driver version 2.0 on, the maximum buffer size can be
changed at program run time, and there is no restriction in size. This driver version is
part of the Linux kernels from version 2.2.7 on. If the new SG driver is available some
backends (e.g. sane-umax(5), sane-mustek(5), sane-sharp(5)) automatically request larger
SCSI buffers. If a backend does not automatically request a larger SCSI buffer, set the
environment variable SANE_SG_BUFFERSIZE to the desired buffer size in bytes. It is not
recommended to use more than 1 MB, because for large values the probability increases that
the SG driver cannot allocate the necessary buffer(s). For ISA cards, even 1 MB might be a
too large value. For a detailed discussion of memory issues of the SG driver, see
http://www.torque.net/sg.

For Linux kernels before version 2.2.7 the size of the buffer is only 32KB. This works,
but for many cheaper scanners this causes scanning to be slower by about a factor of four
than when using a size of 127KB. Linux defines the size of this buffer by macro
SG_BIG_BUFF in header file /usr/include/scsi/sg.h. Unless a system is seriously short on
memory, it is recommended to increase this value to the maximum legal value of
128*1024-512=130560 bytes. After changing this value, it is necessary to recompile both
the kernel (or the SCSI generic module) and the SCSI backends. Keep in mind that this is
only necessary with older Linux kernels.

A common issue with SCSI scanners is what to do when you booted the system while the
scanner was turned off. In such a case, the scanner won't be recognized by the kernel and
SANE won't be able to access it. Fortunately, Linux provides a simple mechanism to probe
a SCSI device on demand. Suppose you have a scanner connected to SCSI bus 2 and the
scanner has a SCSI id of 5. When the system is up and running and the scanner is turned
on, you can issue the command:

echo "scsi add-single-device 2 0 5 0" > /proc/scsi/scsi

and the kernel will probe and recognize your scanner (this needs to be done as root).
It's also possible to dynamically remove a SCSI device by using the
``remove-single-device'' command. For details, please refer to to the SCSI-2.4-HOWTO.

Scanners are known to work with the following SCSI adapters under Linux. This list isn't
complete, usually any SCSI adapter supported by Linux should work.

Acard/Advance SCSI adapters
Some old versions of the kernel driver (atp870u.c) cut the inquiry
information. Therefore the scanner couldn't be detected correctly. Use a
current kernel.

Adaptec AHA-1505/AHA-1542/AHA-2940
Reported to work fine with Linux since v2.0. If you encounter kernel freezes
or other unexpected behaviour get the latest Linux kernel (2.2.17 seems to
work) or reduce SCSI buffer size to 32 kB.

ASUS SC200
Reported to work fine with Linux v2.0.

BusLogic BT958
To configure the BusLogic card, you may need to follow these instructions
(contributed by Jeremy <jeremy@xxedgexx.com>): During boot, when your
BusLogic adapter is being initialized, press Ctrl-B to enter your BusLogic
adapter setup. Choose the address which your BusLogic containing your
scanner is located. Choose ``SCSI Device Configuration''. Choose ``Scan
SCSI Bus''. Choose whatever SCSI id that contains your scanner and then
choose ``View/Modify SCSI configuration''. Change ``Negotiation'' to
``async'' and change ``Disconnect'' to ``off''. Press Esc, save, and Esc
again until you are asked to reboot.

NCR/Symbios 53c400/53c400a or Domex DTC3181E/L/LE (DTCT436/436P) ISA SCSI card
This card is supplied by Mustek (and other vendors). It's supported since
Linux 2.2. The SCSI cards are supported by the module g_NCR5380. It's
necessary to tell the kernel the io port and type of card. Example for a
53c400a: modprobe g_NCR5380 ncr_addr=0x280 ncr_53c400a=1 . Once the kernel
detects the card, it should work all right. However, while it should work,
do not expect good performance out of this card---it has no interrupt line
and therefore while a scan is in progress, the system becomes almost
unusable. You may change the values of the USLEEP macros in
drivers/scsi/g_NCR5380.c. Some documentation is in this file and NCR5380.c.

NCR/Symbios 810
For some scanners it may be necessary to disable disconnect/reconnect. To
achieve this use the option ncr53c8xx="disc:n". Some people reported that
their scanner only worked with the 53c7,8xx driver, not the ncr53c8xx. Try
both if you have trouble.
For Linux kernels before 2.0.33 it may be necessary to increase the SCSI
timeout. The default timeout for the Linux kernels before 2.0.33 is 10
seconds, which is way too low when scanning large area. If you get messages
of the form ``restart (ncr dead ?)'' in your /var/log/messages file or on
the system console, it's an indication that the timeout is too short. In
this case, find the line ``if (np->latetime>10)'' in file ncr53c8xx.
(normally in directory /usr/src/linux/drivers/scsi) and change the constant
10 to, say, 60 (one minute). Then rebuild the kernel/module and try again.

Tekram DC315
The driver can be downloaded from http://www.garloff.de/kurt/linux/dc395/.
For some older scanners it may be necessary to disable all the more advanced
features by using e.g. modprobe dc395x_trm dc395x_trm=7,5,1,32.

Tekram DC390
Version 1.11 of the Tekram driver seems to work fine mostly, except that the
scan does not terminate properly (it causes a SCSI timeout after 10
minutes). The generic AM53C974 also seems to work fine and does not suffer
from the timeout problems.

SOLARIS, OPENSTEP AND NEXTSTEP INFO

       Under Solaris, OpenStep and NeXTStep, the generic SCSI device name refers to a  SCSI  bus,
       not to an individual device.  For example, /dev/sg0 refers to the first SCSI bus.  To tell
       SANE which device to use, append the character 'a'+target-id to the special  device  name.
       For  example,  the SCSI device connected to the first SCSI controller and with target-id 0
       would be called /dev/sg0a, and the device with target-id 1  on  that  same  bus  would  be
       called /dev/sg0b, and so on.

ENVIRONMENT

       SANE_DEBUG_SANEI_SCSI
              If  the  library was compiled with debug support enabled, this environment variable
              controls the debug level for the generic SCSI I/O subsystem.  E.g., a value of  128
              requests  all debug output to be printed by the backend. A value of 255 also prints
              kernel messages from the SCSI subsystem (where available).  Smaller  levels  reduce
              verbosity.

       SANE_SCSICMD_TIMEOUT
              sets  the  timeout value for SCSI commands in seconds. Overriding the default value
              of 120 seconds should only be necessary for very slow scanners.

AUTHOR

       David Mosberger

                                           14 Jul 2008                               sane-scsi(5)