The Raspberry Pi is flashed with the Raspbian OS (quick start guide available here).

The STM32 is flashed with the RTOS ChibiOS. ChibiOS is compact, fast and open source OS : Perfect for me !

STM32F4 Discovery Board

I modified the power connector of the Pi in order to connect it with another connector. As you can see on the architecture document, I will use a small 3.7v Li-Po battery for the Pi and the STM32 with a special power supply (PTN04050C). So I soldered a JST connector with cables :

Brain Power Supply

The Raspberry Pi will will equipped with a “smart switch”. As you are running a Linux on it and a SD-Card, you can not unplug the Pi as you wish. If you shut off your Pi while it is writing on the SD-Card, you might corrupt this one… And you will have to flash it again… 😦

So to prevent this a found what I call a “smart switch” from Mausberry Circuits :

Smart switch

With this switch, you only have to install a small script on the Pi, and that’s it 😉 You can now power ON/OFF your Pi safely !

Concerning the STM32, I can directly use the 5v pin, so i don’t need do modify the board. The STM32 can be shut-down directly without special precaution, so no problem as for the Pi.