SPI communication between slave Arduino and Master Raspberry Pi

Projects Networking, Protocols, and Devices
3

Thank you @Idahowalker for your response.
Yes, theoretically I should be sending these bytes one by one and re-assemble them. Any idea how to do that using SPDR on the arduino side?

On Raspberry Pi side, I can change the buffer array to contain 4 bytes

unsigned char buf[4] = {entered_value, 0, 0, 0};

Then, the last input in the function " wiringPiSPIDataRW" can be changed to 4 as well to receive the 4 bytes.

wiringPiSPIDataRW(SPI_CHANNEL, buf, 4);" function

However, I'm not sure how the code will look like on the Arduino UNO side. I'm not sure how I can send a different byte to the RPi during a 4 bytes single transmission session.