First, the micro-controller and the Raspberry Pi were powered through the key-switch B1-SW2 (5V came from the transformer to the micro-USB of the Raspberry via the switch, and then the ATtiny was powered by the 3.3V of the Raspberry).
But, I was not safe to turn off directly the Raspberry Pi without shut it down (with commands like shutdown).
So, now, the ATtiny is always on (powered by a dedicated 5v-to-3.3v converter), and command a mecanical relay ()