1 - ESP32 - Scope:
In VSPI_initiation.c file Master SPI (VSPI) initiation is implemented.
2 - ESP32 - ESP32 (Master as transmitter):
The Master_transmitter_output.c file sends "A" character to the slave,
and the Slave_receiver_input.c file receives "A" from a master.
3 - ESP32 - ESP32 (Master as receiver):
The Master_receiver.c file receives a string from the slave,
and the Slave_transmitter.c file sends a string to the master.