xref: /freebsd/usr.sbin/i2c/i2c.8 (revision a30555576cd9497620112304600f66643318904c)

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.Dd May 22, 2019
.Dt I2C 8
.Os
.Sh NAME
.Nm i2c
.Nd test I2C bus and slave devices
.Sh SYNOPSIS
.Nm
.Cm -a Ar address
.Op Fl f Ar device
.Op Fl d Ar r|w
.Op Fl w Ar 0|8|16
.Op Fl o Ar offset
.Op Fl c Ar count
.Op Fl m Ar tr|ss|rs|no
.Op Fl b
.Op Fl v
.Nm
.Cm -s
.Op Fl f Ar device
.Op Fl n Ar skip_addr
.Op Fl v
.Nm
.Cm -r
.Op Fl f Ar device
.Op Fl v
.Sh DESCRIPTION
The
.Nm
utility can be used to perform raw data transfers (read or write) with devices
on the I2C bus. It can also scan the bus for available devices and reset the
I2C controller.
.Pp
The options are as follows:
.Bl -tag -width ".Fl d Ar direction"
.It Fl a Ar address
7-bit address on the I2C device to operate on (hex).
.It Fl b
binary mode - when performing a read operation, the data read from the device
is output in binary format on stdout; when doing a write, the binary data to
be written to the device is read from stdin.
.It Fl c Ar count
number of bytes to transfer (dec).
.It Fl d Ar r|w
transfer direction: r - read, w - write.
.It Fl f Ar device
I2C bus to use (default is /dev/iic0).
.It Fl m Ar tr|ss|rs|no
addressing mode, i.e., I2C bus operations performed after the offset for the
transfer has been written to the device and before the actual read/write
operation.
.Bl -tag -compact -offset indent
.It Va tr
complete-transfer
.It Va ss
stop then start
.It Va rs
repeated start
.It Va no
none
.El
Some I2C bus hardware does not provide control over the individual start,
repeat-start, and stop operations.
Such hardware can only perform a complete transfer of the offset and the
data as a single operation.
The
.Va tr
mode creates control structures describing the transfer and submits them
to the driver as a single complete transaction.
This mode works on all types of I2C hardware.
.It Fl n Ar skip_addr
skip address - address(es) to be skipped during bus scan.
There are two ways to specify addresses to ignore: by range 'a..b' or
using selected addresses 'a:b:c'. This option is available only when "-s" is
used.
.It Fl o Ar offset
offset within the device for data transfer (hex).
The default is zero.
Use
.Dq -w 0
to disable writing of the offset to the slave.
.It Fl r
reset the controller.
.It Fl s
scan the bus for devices.
.It Fl v
be verbose.
.It Fl w Ar 0|8|16
device addressing width (in bits).
This is used to determine how to pass
.Ar offset
specified with
.Fl o
to the slave.
Zero means that the offset is ignored and not passed to the slave at all.
.El
.Sh WARNINGS
Great care must be taken when manipulating slave I2C devices with the
.Nm
utility. Often times important configuration data for the system is kept in
non-volatile but write enabled memories located on the I2C bus, for example
Ethernet hardware addresses, RAM module parameters (SPD), processor reset
configuration word etc.
.Pp
It is very easy to render the whole system unusable when such configuration
data is deleted or altered, so use the
.Dq -d w
(write) command only if you know exactly what you are doing.
.Pp
Also avoid ungraceful interrupting of an ongoing transaction on the I2C bus,
as it can lead to potentially dangerous effects. Consider the following
scenario: when the host CPU is reset (for whatever reason) in the middle of a
started I2C transaction, the I2C slave device could be left in write mode
waiting for data or offset to arrive. When the CPU reinitializes itself and
talks to this I2C slave device again, the commands and other control info it
sends are treated by the slave device as data or offset it was waiting for,
and there's great potential for corruption if such a write is performed.
.Sh EXAMPLES
.Bl -bullet
.It
Scan the default bus (/dev/iic0) for devices:
.Pp
i2c -s
.It
Scan the default bus (/dev/iic0) for devices and skip addresses 0x56 and
0x45.
.Pp
i2c -s -n 0x56:0x45
.It
Scan the default bus (/dev/iic0) for devices and skip address range
0x34 to 0x56.
.Pp
i2c -s -n 0x34..0x56
.It
Read 8 bytes of data from device at address 0x56 (e.g., an EEPROM):
.Pp
i2c -a 0x56 -d r -c 8
.It
Write 16 bytes of data from file data.bin to device 0x56 at offset 0x10:
.Pp
i2c -a 0x56 -d w -c 16 -o 0x10 -b < data.bin
.It
Copy 4 bytes between two EEPROMs (0x56 on /dev/iic1 to 0x57 on /dev/iic0):
.Pp
i2c -a 0x56 -f /dev/iic1 -d r -c 0x4 -b | i2c -a 0x57 -f /dev/iic0 -d w -c 4 -b
.It
Reset the controller:
.Pp
i2c -f /dev/iic1 -r
.El
.Sh SEE ALSO
.Xr iic 4 ,
.Xr iicbus 4
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 8.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
utility and this manual page were written by
.An Bartlomiej Sieka Aq Mt tur@semihalf.com
and
.An Michal Hajduk Aq Mt mih@semihalf.com .