spi.c

#include "spi.h"

void spi_init(void) {
    USICR &= ~(_BV(USISIE) | _BV(USIOIE) | _BV(USIWM1));
    USICR |= _BV(USIWM0) | _BV(USICS1) | _BV(USICLK);
    SPI_DDR_PORT |= _BV(SCK_DD_PIN);        //set the USCK pin as output
    SPI_DDR_PORT |= _BV(SDO_DD_PIN);        //set the DO pin as output
    SPI_DDR_PORT &= ~_BV(SDI_DD_PIN);       //set the DI pin as input
}

void spi_setDataMode(uint8_t spiDataMode) {
    if (spiDataMode == SPI_MODE1)
        USICR |= _BV(USICS0);
    else
        USICR &= ~_BV(USICS0);
}

uint8_t spi_transfer(uint8_t spiData) {
    USIDR = spiData;
    USISR = _BV(USIOIF);                    //clear counter and counter overflow interrupt flag
    ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {     //ensure a consistent clock period
        while (!(USISR & _BV(USIOIF))) {
            USICR |= _BV(USITC);            // Toggle SCK full speed, until USIOIF is set (all data exchanged)
        }

    }
    return USIDR;
}

void spi_end(void) {
    USICR &= ~(_BV(USIWM1) | _BV(USIWM0));
}