from machine import Pin, SPI

# Initialize SPI0 as a Target (Slave)
spi = SPI(0, baudrate=100000, polarity=0, phase=0, sck=Pin(2), mosi=Pin(3), miso=Pin(4))
cs = Pin(5, Pin.IN, Pin.PULL_UP) # Listen for CS signal

print("Waiting for data...")

while True:
    # Wait for the Controller to pull the CS pin low
    if cs.value() == 0:
        # Create a buffer to read incoming data
        data = bytearray(3)
        spi.write_readinto(bytearray(3), data)
        
        # Make sure transmission is complete
        while cs.value() == 0:
            pass 
            
        print("Received:", list(data))