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i2c-star - A STM32 based clone of the i2c-tiny-usb

i2c-star is a compatible clone of Till Harbaum’s i2c-tiny-usb. The firmware has no software in common with Till’s implementation but is compatible with the i2c-tiny-usb driver found in the mainline Linux kernel. As a result it will work out of the box without requiring any special software on the host computer.

Quickstart

  • Install gcc-arm-embedded compiler toolchain (or similar arm-none-eabi- compiler), openocd and dfu-util.

  • Clone this repo: git clone https://github.com/daniel-thompson/i2c-star.git

  • Fetch the libraries: cd i2c-star; git submodule update --init --recursive

  • Build the firmware:

  • make

  • Use a JTAG/SWD programmer to install the booloader. Either make -C src/bootloader flash for STLink v2 or make -C src/bootloader BMP_PORT=/dev/ttyACM0 flash for a Black Magic Probe.

  • Use the bootloader to install the main application using the microcontroller board’s own USB socket: make -C src/i2c-stm32f1-usb flash

Examples

Note that the i2c_dev kernel module needs to be loaded before using any of the i2c-tools utilities.

$ i2cdetect -l
...
i2c-7   unknown         i2c-tiny-usb at bus 001 device 031      N/A
$ i2cdetect -y 7

To make Linux aware of I2C devices on the bus, use the following command:

$ echo tmp102 0x48 | sudo tee /sys/class/i2c-adapter/i2c-7/new_device

Where tmp102 is the name of the kernel driver you want to associate with the I2C device, 0x48 is the I2C device’s 7-bit address, and i2c-7 is the bus number the kernel assigned to the i2c-star adapter (appears as i2c-tiny-usb in dmesg and i2cdetect).

Hardware setup

The firmware can be easily ported but has been tested on an small STM32F103C8T6 based breakout board. Connections required are:

  • USB to host computer

  • B7: I2C bus SDA and B6: I2C bus SCL (don’t forget pull up resistors)

  • [Optional; debug only] PA9: UART TX and PA10: UART RX

It has also been tested on the STM32F4-Discovery board, where no connections (except for USB) are required because this board has I2C peripherals built in

Example hardware

STM32F103C8T6 microcontroller development board from vcc-gnd.com. Normally very easy to source on eBay.

STM32F103C8T6 microcontroller development board