I2C interface

This RP2040 firmware implements the USB protocol expected by the I2C-Tiny-USB kernel driver, allowing the use of a Raspberry Pi Pico as USB to I2C adapter.

The original I2C-Tiny-USB project can be found at https://github.com/harbaum/I2C-Tiny-USB, this firmware is a complete re-implementation of the firmware for use with the RP2040.

More testing is needed to verify that the firmware works correctly, this project currently has proof of concept status.

To compile and flash

Be sure you have your PICO_SDK_PATH env variable pointing to the root of the Pico SDK.

Set your PICO_BOARD env variable to one of the supported boards in ${PICO_SDK_PATH}/src/boards/include/boards.

Note: before compiling, plug in your pico and set it in programming mode (RESET + BOOT then release RESET, release BOOT and it should appear as a block device). You might need root priviledge or be in a specific group on your distrib to be able to do that.

For example:

PICO_BOARD=waveshare_rp2040_zero make

Pinout

It will depend on your mappings for your board.

If you are unsure, make will give you what it has configured for your board:

[...]
PICO_SDK_PATH set to: /usr/share/pico-sdk
PICO_BOARD set to: pico
For this board:
-> SDA is pin 4.
-> SCL is pin 5.
[...]

Note: It will default to 2 and 3 if not found in the board definition file.

Expected behavior

Check your i2c devices prior to plug in the device:

$ ls -la /dev/i2c*                                                                                                                                                                                  
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-0                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-1                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-2                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-3                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-4                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-5                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-6                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-7                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-8

Once plugged in, it should appear as an extra i2c device:

$ ls -la /dev/i2c*                                                                                                                                                                                  
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-0                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-1                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-2                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-3                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-4                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-5                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-6                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-7                                                                                                                                                                           
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-8
crw-rw----+ root i2c 0 B Tue Jan  9 07:51:12 2024  /dev/i2c-9 <==