Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
SMBMSG(8)               FreeBSD System Manager's Manual              SMBMSG(8)

     smbmsg - send or receive messages over an SMBus

     smbmsg [-f dev] -p

     smbmsg [-f dev] -s slave [-F fmt] [-c cmd] [-w] [-i incnt] [-o outcnt]
            [outdata ...]

     The smbmsg utility can be used to send or receive messages over an SMBus,
     see smbus(4).

     The smbmsg utility has two different modi of operation.  The first form
     shown in the synopsis can be used to ``probe'' the devices on the SMBus.
     This is done by sending each valid device address one receive byte, and
     one quick read message, respectively.  Devices that respond to these
     requests will by displayed by their device address, followed by the
     strings `r', `w', or `rw', for devices that are readable, writeable, or
     both, readable and writeable, respectively.  The only valid additional
     option for this modus of operation (besides the -p option that choses the
     modus) is -f dev.  See below for a description.

     Note that probing the bus is risky, since individual devices could
     perform unwanted actions upon receiving one of the mentioned messages.
     For example, if a particular SMBus device considers any write operation
     issued to it as a request to power off the system, the probing would
     trigger this action.

     The second form shown in the synopsis can be used to send or receive
     arbitrary messages to or from individual devices.  This might be useful
     to explore individual devices on the SMBus, or maybe even to write short
     shell scripts performing maintenance operations on the bus.

     Any data values on the command-line are integer values in the range 0
     through 255 for byte values, or 0 through 65535 for word values.  They
     can be specified using standard `C' notation (prefix 0 for octal
     interpretation, or 0x for hexadecimal interpretation).

     Since the low-order bit of the device address of SMBus devices selects
     between read and write operations, only even-numbered slave addresses can
     exist on the bus.

     The options are as follows:

     -F fmt           Specify the printf(3) format to be used for displaying
                      input data.  This option is ignored in messages that do
                      not read any input from the SMBus device.  The format
                      defaults to `0x%02x' for byte input operations, and to
                      `0x%04x' for word input operations.  For multi-byte
                      input (block read), the same format is used for each
                      individual byte read from the SMBus.

     -c cmd           This is the value of the command byte to be issued as
                      part of the SMBus message.

     -f dev           This specifies that dev should be used as the connection
                      to the SMBus, rather than the default of /dev/smb0.

     -i incnt         An SMBus message should be generated to read incnt bytes
                      from the device.

     -o outcnt        An SMBus message should be generated to write outcnt
                      bytes to the device.  The data values to write are
                      expected to follow all of the options (and their
                      arguments) on the command-line, where the number of data
                      bytes must match the outcnt value.

     -p               This selects the probe bus modus of operation.

     -s slave         The slave parameter specifies which SMBus device to
                      connect to.  This option also selects the transfer
                      messages from/to device modus of operation, where a
                      slave address is mandatory.

     -w               This option specifies that IO operations are word
                      operations, rather than byte operations.  Either incnt,
                      or outcnt (or both) must be equal 2 in this case.  Note
                      that the SMBus byte order is defined to be little-endian
                      (low byte first, high byte follows).

     Not all argument combinations make sense in order to form valid SMBus
     messages.  If no -c cmd option has been provided, the following messages
     can be issued:

           message        incnt   outcnt
           quick read         0        -
           quick write        -        0
           receive byte       1        -
           send byte          -        1

     Note in particular that specifying 0 as a count value has a different
     meaning than omitting the respective option entirely.

     If a command value has been given using the -c cmd option, the following
     messages can be generated:

           message        -w    incnt   outcnt
           read byte      no        1        -
           write byte     no        -        1
           read word      yes       2        -
           write word     yes       -        2
           process call   yes       2        2
           block read     no     >= 2        -
           block write    no        -     >= 2

     /dev/smb0      The default device to connect to, unless -f dev has been

     Typical usage examples of the smbmsg command include:

           smbmsg -f /dev/smb1 -p

     Probe all devices on the SMBus attached to /dev/smb1.

           smbmsg -s 0x70 -i 1

     Issue a receive byte message to the device at address 0x70, and display
     the received byte using the default format.

           smbmsg -s 0x70 -c 0xff -i 1 -F %d

     Issue a read byte message to the device at slave address 0x70, using 255
     (0xff) as the command-byte to send to the device, and display the result
     using the custom format `%d'.

           smbmsg -s 0xa0 -c 0 -o 1 0x80

     Send a write byte message to the slave device at address 0xa0, using 0 as
     the command-byte value, and 0x80 as the byte to send (after the command).
     Assuming this might be a Philips PCF8583 real-time clock, this would stop
     the clock.

           smbmsg -s 0xa0 -c 1 -i 6 -F %02x

     Send a block read command to device at address 0xa0, and read 6 bytes
     from it, using hexadecimal display.  Again, assuming a PCF8583 RTC, this
     would display the fractions of second, seconds, minutes, hours,
     year/date, and weekday/month values.  Since this RTC uses BCD notation,
     the actual values displayed were decimal then.

           smbmsg -s 0xa0 -c 2 -o 5 0x00 0x07 0x22 0x16 0x05

     Send a block write command to device at address 0xa0.  For the PCF8583
     RTC, this would set the clock to Sunday (2004%4)-05-16 22:07:00.

     Exit status is 0 on success, or according to sysexits(3) in case of
     failure.  Diagnostic messages issued are supposed to be self-explanatory.

     printf(3), sysexits(3), smb(4), smbus(4)

     The SMBus specification,

     The smbmsg utility first appeared in FreeBSD 5.3.

     The smbmsg utility and this manual page were written by Jorg Wunsch.

FreeBSD 11.0-PRERELEASE          May 16, 2004          FreeBSD 11.0-PRERELEASE


Want to link to this manual page? Use this URL:

home | help