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)