typedef enum { CTL_SPI_CPOL_0, CTL_SPI_CPOL_1, CTL_SPI_CPHA_0, CTL_SPI_CPHA_1, CTL_SPI_MODE0, CTL_SPI_MODE1, CTL_SPI_MODE2, CTL_SPI_MODE3 } CTL_SPI_MODE_t;
CTL_SPI_MODE_t defines the four operating modes of the SPI bus, 0 through 3.