ESP32 has 4 SPI controllers. They are SPI0、SPI1、SPI2、SPI3. SPI0 can be used to access to the external storage unit as a fast cache. SPI1 can be used as the Master host. SPI2, SPI3 can be used as both Master and Slave. SPI0 and SPI1 share one BUS prefixed with "SPI", they consist of signals "D, Q, CS...