I am working with two types of STM boards - Stm32f3 and Stm32E407. On both the boards, I am using I2C in the multi master configuration. In this configuration, I can connect multiple boards to the same I2C bus with unique 7 bit addresses for each board. I am using the transciever module to abstract the I2C bus from the upper layers. I make the I2C bus look like an 802.15.4 radio using the radio packet type definition. On the second board, STM32E407, from Olimex, has an Ethernet connection and I pass the Ethernet packets directly to the IP layer.

Regards, Abhinav