Hi,
no I confirm, this is an official brand "arduino.org" see attachment.
I was inspired by your example and others.
And so the pins GPIO8, 11, 26 or 27 can still be used to make a handshake provided you validate the level shifter outputs by exporting and setting high the GPIO21 pin of the Atheros.
example with the "D17/PB0/RxLED/SS" of the ATMega.
Add these lines to your /etc/rc.local
export 21 > /sys/class/gpio/gpio21/export
echo 1 > /sys/class/gpio/gpio21/direction
echo 1 > /sys/class/gpio/gpio21/value
export 26 > /sys/class/gpio/gpio26/export
echo 1 > /sys/class/gpio/gpio26/direction
echo 1 > /sys/class/gpio/gpio26/value
Then I created a code and a sketch in C to connect the processor (Master) with the microcontroller (slave) through the SPI.
It would be useful for someone to translate it into python on the linux side...
See attachment.
Thanks
ATmega_SPI_Slave_Hardware.ino (1.99 KB)
Atheros_SPI_Master.c (4.09 KB)
Atheros_SPI_Master_py.txt (227 Bytes)