smbmsg(8)

NAME

smbmsg - send or receive messages over an SMBus

SYNOPSIS

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

DESCRIPTION

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 re

ceive 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 prob

ing 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 de

vices 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 mes

sages that do
not read any input from the SMBus device.

The format
defaults to `0x%02x' for byte input opera

tions, 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 num

ber of data
bytes must match the outcnt value.

-p This selects the probe bus modus of opera

tion.

-s slave The slave parameter specifies which SMBus

device to con

nect 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 opera

tions, 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 fol

lowing 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

FILES

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

dev has been

provided.

EXIT STATUS

Exit status is 0 on success, or according to sysexits(3) in

case of failure.

EXAMPLES

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 dis

play 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.

DIAGNOSTICS

Diagnostic messages issued are supposed to be self-explana

tory.

SEE ALSO

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

The SMBus specification, http://www.smbus.org/specs/.

HISTORY

The smbmsg utility first appeared in FreeBSD 5.3.

AUTHORS

The smbmsg utility and this manual page were written by Jorg

Wunsch.

BSD May 16, 2004

BSD