Bash Shell Interface for I2C

On the kernel level, I2C communication is handled by the i2c-dev kernel driver. On the lowest level, the bus is seen as a file and using a file descriptor one can read from it or write to it. The shell interface is a set of compiled programs that wrap this functionality for specific uses at a higher level. The intended use is interactive debugging to see if something works or not. For programmatic use it's better to take a look at the C API for C/C++ and the smbus2 library for Python.

These programs are part of the i2c-tools package that usually comes preinstalled in most Linux distributions.

Detects I2C chips. Use: i2cdetect [options] i2cbus [first_addr last_addr]. Special flags that don't require a given i2cbus are -V that prints the current version and -l.

• i2cdetect -l to list busses. To access each buss you have to used it's number (i2c-{NUM}) or the full string name.
• -q and -r options are to use quick write and receive byte commands for probing. They can corrupt certain IC chips.
• -F displays the list of functionalities available on the bus.

Examines registers on the I2C bus. Use: i2cdump [options] i2cbus address [mode [bank [bankreg]]]

• i2cbus: One of the buses represented by the number or string name from i2cdetect -l.
• -r first-last: Limit the range of registers being accessed. Incompatible with s.
• address: The address of the IC chip on the bus.
• mode: Chooses the mode to access the register as a single byte, a double byte word or a block. If not provided, defaults to single byte without PEC. Options are listed below:
  • b: Single byte (default).
  • w: Word.
  • i: I2C block.
  • c: Consecutive block. Useful for ICs with automatic increment, like EEPROMs.
  • W: Word, but the command will only be issued on even addresses. Also useful for EEPROMs.
  • s: SMBus block. Avoid it, it's deprecated.
  • p: Can be appended on the mode parameter (not on i and W) to enable Packet Error Checking (PEC).
• bank/bankreg: Used on Winbond and Asus chips. bank is an integer from 0 to 7, and bankreg an integer from 0x00 to 0xff with a default of 0x4e.

Use of i2cdump is not advised unless you have intimate knowledge of the IC you're accessing. It's very easy to corrupt stuff.

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