Axoloti uses the following gpio pins for i2c. The Hohum Axoctrl already uses I2C for the display. So you will have to communicate to the Arduino on an other address on the i2c bus, and probably solder some extra wires to these pins to connect to your Arduino.
- PB9 = SDA (Data Signal)
- PB8 = SCL (Clock Signal)
Chibios is the RTOS (real time operating system) used on the Axoloti.
I2C driver code from the Axoloti firmware can be found here.:
You will also need to write custom code for the Arduino in order to interpret the data coming from the Axoloti, since it won't know by default what the ones and zeroes you are sending mean.
This is a good tutorial to learn about i2c communication between two arduinos.
Not exactly something I would recommend as a first coding project, but good luck.