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I2C

Each CPU supports a number of I2C bus interfaces. In some cases, more I2C interfaces exist on the CPU and can be enabled in the device tree file. The table below is a mapping between the bus numbering in U-Boot / Linux and the I2C channel name (A/B/C/) used on the SOM Carrier board. Note that the bus numbering in U-Boot/Linux is not necessarily the same as the peripheral number on the processor.

BoardI2C-AI2C-BI2C-CI2C-D
RX/G3E SOMi2c-8i2c-3i2c-1i3c - see I3C

Which I2C devices that can be found varies depending on SOM board, SOM Carrier Board and connected peripherals like displays (typically the touch controller uses I2C).

The 7-bit address of all I2C devices on the SOM Carrier board can be found in the schematics for the SOM Carrier board.

U-Boot​

i2c
i2c - I2C sub-system

Usage:
i2c bus [muxtype:muxaddr:muxchannel] - show I2C bus info
i2c crc32 chip address[.0, .1, .2] count - compute CRC32 checksum
i2c dev [dev] - show or set current I2C bus
i2c loop chip address[.0, .1, .2] [# of objects] - looping read of device
i2c md chip address[.0, .1, .2] [# of objects] - read from I2C device
i2c mm chip address[.0, .1, .2] - write to I2C device (auto-incrementing)
i2c mw chip address[.0, .1, .2] value [count] - write to I2C device (fill)
i2c nm chip address[.0, .1, .2] - write to I2C device (constant address)
i2c probe [address] - test for and show device(s) on the I2C bus
i2c read chip address[.0, .1, .2] length memaddress - read to memory
i2c write memaddress chip address[.0, .1, .2] length [-s] - write memory
          to I2C; the -s option selects bulk write in a single transaction
i2c flags chip [flags] - set or get chip flags
i2c olen chip [offset_length] - set or get chip offset length
i2c reset - re-init the I2C Controller
i2c speed [speed] - show or set I2C bus speed

To see the available busses.

i2c bus
Bus 3:  i2c@14401000
Bus 8:  i2c@11C01000  (active 8)
   21: gpio@21, offset len 1, flags 0
   23: gpio@23, offset len 1, flags 0
   22: gpio@22, offset len 1, flags 0
   38: generic_38, offset len 1, flags 0

To list all devices on bus 8.

i2c dev 8
Setting bus to 8
i2c probe
Valid chip addresses: 12 1A 52 55 6F

The scan found the following devices.

  • 0x12 – PMIC on the SOM board
  • 0x1a – Audio Codec on the SOM Carrier Board
  • 0x52 – EUI-48 EEPROM on the SOM Carrier Board
  • 0x55 – EEPROM on the SOM Board
  • 0x6F – PMIC on the SOM board

Note that your result may be different depending on which combination of SOM board, SOM Carrier Board and external peripherals you use.

Linux​

To see which I2C busses are available list content in dev directory.

ls /dev/i2c*
/dev/i2c-1  /dev/i2c-3  /dev/i2c-8

You can also use the i2cdetect command.

i2cdetect -l
i2c-1   i2c   Renesas RIIC adapter       I2C adapter
i2c-3   i2c   Renesas RIIC adapter       I2C adapter
i2c-8   i2c   Renesas RIIC adapter       I2C adapter

To scan for all devices on i2c-8.

i2cdetect -y 8
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- 12 -- -- -- -- -- -- -- UU -- -- -- -- --
20: -- UU UU UU -- -- -- -- 28 -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- 38 -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- UU -- -- UU -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- 6f
70: -- -- -- -- -- -- -- --

The scan above uses UU to indicate that a device was not probed as it was marked as being in use by a driver. The address to device mapping is described in the U-Boot section above.