I have no UARTs left on the ATmega and need to deliver 1 Byte of information from the pi using 1 analog input. I2C is no option either.
I planned using the digital output to request an analog signal from the Pi, but it does not seem to have a DAC.
Is it possible to properly translate/read a PWM signal with the atmegas ADC? Analyzing the PWM the 'usual' way would probably be too slow as I don't trust the pi to keep up with a high PWM frequency.
PINS left: PA0(ADC0|PCINT0), PD7(OC2A|PCINT31)
I should add that this is a rather large robotics project involving communication between 8 MCUs in it's current state and needs to be extended by a computer vision module(=pi), which is not compatible with the existing custom bus
Edit: This also is a real time system which has approximately ~1-2ms left in it's main loop(10ms period). The required data has to be present in time as it alters the robot's behaviour for this loop.