The HiPi::BCM2835::I2C module provides access to i2c devices including those that require repeated start signals before a read can take place. It also allows you to enable or disable individual i2c buses so that for Model B Rev 2 and Model A boards you can enable a second i2c bus on the P5 header. ( see :Second I2C Bus).
To allow access to this facility from outside your Perl scripts HiPi modules installs a utility application hipi-i2c (
The utility is installed with setuid permission so allways runs as root allowing the necessary access to the i2c hardware peripherals on the Pi.
The calling process user must be a member of the group i2c to execute the utility.
You can manage group membership with the HiPi Control Gui.
usage : hipi-i2c MODE I2C [ADDRESS] [REGISTER] [BAUDRATE] [ARG1 ARG2 ARG3] MODE = w[rite] | r[read] | h[elp] | b[aud] | e[nable] I2C = 0 | 1 The i2c perphipheral to use ADDRESS = The device address on the i2c bus when mode r|w REGISTER = The register on the device you wish to write to / read from when mode r|w BAUDRATE = Baudrate for I2C ( only root may change baudrate); ARG1,2,n = additional arguments Examples: We have a device at address 0x3A on the I2C-1 peripheral. (default for Model B Revision 2.0 and Model A boards.) write one byte (0xFF) to register 0x02 hipi-i2c w 1 0x3A 0x02 0xFF write just the register address (0x02) to the device hipi-i2c w 1 0x3A 0x02 write 3 bytes (0xFF, 0xFE, 0x11) to register 0x02 hipi-i2c w 1 0x3A 0x02 0xFF 0xFE 0x11 read 1 byte starting at register 0x09 hipi-i2c r 1 0x3A 0x09 1 read 24 bytes starting at register 0x09 hipi-i2c r 1 0x3A 0x09 24 set baudrate to 400000 on I2C peripheral 1 sudo hipi-i2c b 1 400000 get current baudrate on I2C peripheral 1 hipi-i2c b 1 enable i2c bus 1 hipi-i2c e 1 1 enable i2c bus 0 hipi-i2c e 0 1 disable i2c bus 0 hipi-i2c e 0 0 Calls to read return a list of space separated byte values on stdout. Calls to write return the number of bytes written on stdout. The register address passed to the write command counts as one byte (it is possible to write only the register address) so the command hipi-i2c w 1 0x3A 0x02 0xFF will return '2' on success. Calls to baud, whether set or get, always return the baudrate from the hardware peripheral on stdout. Because the baudrate is converted to a divider for the system clock on set, and then converted back to a baudrate on get, the number you get back will not always be exactly the number that you set. Allowed baudrate settings are in the range 500 to 1600000 ( near the maximum the Broadcom peripheral supports). You may see problems at speeds over 1MHz ( 1000000 ) even if your device claims to support it. Common values for baudrate are: 100000 - the i2c standard 400000 - fast i2c standard 1000000 - seems to be the fastest reliable speed that this implementation supports. Of course, all the devices on your bus must support this too. 32000 - the Broadcom I2C peripherals don't support clock stretching so if you have a device that employs this, a baudrate of 32000 ( or perhaps even lower ) will often allow the device to work. Calls to enable allow you to disable and enable the available I2C buses. Parameters are e(command) bus(0 or 1) enable(0 or 1) So to disable bus 1 hipi-i2c e 1 0 to enable bus 0 hipi-i2c e 0 1 See also : Second I2C Bus On error, the utility will exit with a none zero value.