xref: /freebsd/usr.sbin/i2c/i2c.8 (revision 39beb93c) 
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26.\" $FreeBSD$
27.\"
28
29.Dd Jan 23, 2009
30.Dt I2C 8
31.Os
32.Sh NAME
33.Nm i2c
34.Nd test I2C bus and slave devices
35.Sh SYNOPSIS
36.Nm
37.Cm -a Ar address
38.Op Fl f Ar device
39.Op Fl d Ar r|w
40.Op Fl w Ar 0|8|16
41.Op Fl o Ar offset
42.Op Fl c Ar count
43.Op Fl m Ar ss|rs|no
44.Op Fl b
45.Op Fl v
46.Nm
47.Cm -s
48.Op Fl f Ar device
49.Op Fl n Ar skip_addr
50.Op Fl v
51.Nm
52.Cm -r
53.Op Fl f Ar device
54.Op Fl v
55.Sh DESCRIPTION
56The
57.Nm
58utility can be used to perform raw data transfers (read or write) with devices
59on the I2C bus. It can also scan the bus for available devices and reset the
60I2C controller.
61.Pp
62The options are as follows:
63.Bl -tag -width ".Fl d Ar direction"
64.It Fl a Ar address
657-bit address on the I2C device to operate on (hex).
66.It Fl b
67binary mode - when performing a read operation, the data read from the device
68is output in binary format on stdout; when doing a write, the binary data to
69be written to the device is read from stdin.
70.It Fl c Ar count
71number of bytes to transfer (dec).
72.It Fl d Ar r|w
73transfer direction: r - read, w - write.
74.It Fl f Ar device
75I2C bus to use (default is /dev/iic0).
76.It Fl m Ar ss|rs|no
77addressing mode, i.e., I2C bus operations performed after the offset for the
78transfer has been written to the device and before the actual read/write
79operation. rs - repeated start; ss - stop start; no - none.
80.It Fl n Ar skip_addr
81skip address - address(es) to be skipped during bus scan.
82The are two ways to specify addresses to ignore: by range 'a..b' or
83using selected addresses 'a:b:c'. This option is available only when "-s" is
84used.
85.It Fl o Ar offset
86offset within the device for data transfer (hex).
87.It Fl r
88reset the controller.
89.It Fl s
90scan the bus for devices.
91.It Fl v
92be verbose
93.It Fl w Ar 0|8|16
94device addressing width (in bits).
95.El
96.Sh WARNINGS
97Great care must be taken when manipulating slave I2C devices with the
98.Nm
99utility. Often times important configuration data for the system is kept in
100non-volatile but write enabled memories located on the I2C bus, for example
101Ethernet hardware addresses, RAM module parameters (SPD), processor reset
102configuration word etc.
103.Pp
104It is very easy to render the whole system unusable when such configuration
105data is deleted or altered, so use the
106.Dq -d w
107(write) command only if you know exactly what you are doing.
108.Pp
109Also avoid ungraceful interrupting of an ongoing transaction on the I2C bus,
110as it can lead to potentially dangerous effects. Consider the following
111scenario: when the host CPU is reset (for whatever reason) in the middle of a
112started I2C transaction, the I2C slave device could be left in write mode
113waiting for data or offset to arrive. When the CPU reinitializes itself and
114talks to this I2C slave device again, the commands and other control info it
115sends are treated by the slave device as data or offset it was waiting for,
116and there's great potential for corruption if such a write is performed.
117.Sh EXAMPLES
118.Pp
119.Bl -bullet
120.It
121Scan the default bus (/dev/iic0) for devices:
122.Pp
123i2c -s
124.It
125Scan the default bus (/dev/iic0) for devices and skip addresses 0x56 and
1260x45.
127.Pp
128i2c -s -n 0x56:0x45
129.It
130Scan the default bus (/dev/iic0) for devices and skip address range
1310x34 to 0x56.
132.Pp
133i2c -s -n 0x34..0x56
134.It
135Read 8 bytes of data from device at address 0x56 (e.g., an EEPROM):
136.Pp
137i2c -a 0x56 -d r -c 8
138.It
139Write 16 bytes of data from file data.bin to device 0x56 at offset 0x10:
140.Pp
141i2c -a 0x56 -d w -c 16 -o 0x10 -b < data.bin
142.It
143Copy 4 bytes between two EEPROMs (0x56 on /dev/iic1 to 0x57 on /dev/iic0):
144.Pp
145i2c -a 0x56 -f /dev/iic1 -d r -c 0x4 -b | i2c -a 0x57 -f /dev/iic0 -d w -c 4 -b
146.It
147Reset the controller:
148.Pp
149i2c -f /dev/iic1 -r
150.El
151.Sh SEE ALSO
152.Xr iic 4 ,
153.Xr iicbus 4
154.Sh HISTORY
155The
156.Nm
157utility appeared in
158.Fx 8.0 .
159.Sh AUTHORS
160.An -nosplit
161The
162.Nm
163utility and this manual page were written by
164.An Bartlomiej Sieka
165.Aq tur@semihalf.com
166and
167.An Michal Hajduk
168.Aq mih@semihalf.com .
169