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33 .Nd test I2C bus and slave devices
42 .Op Fl m Ar tr|ss|rs|no
57 utility can be used to perform raw data transfers (read or write) with devices
58 on the I2C bus. It can also scan the bus for available devices and reset the
61 The options are as follows:
62 .Bl -tag -width ".Fl d Ar direction"
64 7-bit address on the I2C device to operate on (hex).
66 binary mode - when performing a read operation, the data read from the device
67 is output in binary format on stdout; when doing a write, the binary data to
68 be written to the device is read from stdin.
70 number of bytes to transfer (dec).
72 transfer direction: r - read, w - write.
74 I2C bus to use (default is /dev/iic0).
75 .It Fl m Ar tr|ss|rs|no
76 addressing mode, i.e., I2C bus operations performed after the offset for the
77 transfer has been written to the device and before the actual read/write
79 .Bl -tag -compact -offset indent
89 Some I2C bus hardware does not provide control over the individual start,
90 repeat-start, and stop operations.
91 Such hardware can only perform a complete transfer of the offset and the
92 data as a single operation.
95 mode creates control structures describing the transfer and submits them
96 to the driver as a single complete transaction.
97 This mode works on all types of I2C hardware.
99 skip address - address(es) to be skipped during bus scan.
100 There are two ways to specify addresses to ignore: by range 'a..b' or
101 using selected addresses 'a:b:c'. This option is available only when "-s" is
104 offset within the device for data transfer (hex).
108 to disable writing of the offset to the slave.
110 reset the controller.
112 scan the bus for devices.
116 device addressing width (in bits).
117 This is used to determine how to pass
122 Zero means that the offset is ignored and not passed to the slave at all.
125 Great care must be taken when manipulating slave I2C devices with the
127 utility. Often times important configuration data for the system is kept in
128 non-volatile but write enabled memories located on the I2C bus, for example
129 Ethernet hardware addresses, RAM module parameters (SPD), processor reset
130 configuration word etc.
132 It is very easy to render the whole system unusable when such configuration
133 data is deleted or altered, so use the
135 (write) command only if you know exactly what you are doing.
137 Also avoid ungraceful interrupting of an ongoing transaction on the I2C bus,
138 as it can lead to potentially dangerous effects. Consider the following
139 scenario: when the host CPU is reset (for whatever reason) in the middle of a
140 started I2C transaction, the I2C slave device could be left in write mode
141 waiting for data or offset to arrive. When the CPU reinitializes itself and
142 talks to this I2C slave device again, the commands and other control info it
143 sends are treated by the slave device as data or offset it was waiting for,
144 and there's great potential for corruption if such a write is performed.
148 Scan the default bus (/dev/iic0) for devices:
152 Scan the default bus (/dev/iic0) for devices and skip addresses 0x56 and
157 Scan the default bus (/dev/iic0) for devices and skip address range
162 Read 8 bytes of data from device at address 0x56 (e.g., an EEPROM):
164 i2c -a 0x56 -d r -c 8
166 Write 16 bytes of data from file data.bin to device 0x56 at offset 0x10:
168 i2c -a 0x56 -d w -c 16 -o 0x10 -b < data.bin
170 Copy 4 bytes between two EEPROMs (0x56 on /dev/iic1 to 0x57 on /dev/iic0):
172 i2c -a 0x56 -f /dev/iic1 -d r -c 0x4 -b | i2c -a 0x57 -f /dev/iic0 -d w -c 4 -b
174 Reset the controller:
190 utility and this manual page were written by
191 .An Bartlomiej Sieka Aq Mt tur@semihalf.com
193 .An Michal Hajduk Aq Mt mih@semihalf.com .