xyFC/src/spi.c

/*
 * Bit-Banged SPI routines
 */

#include "spi.h"

void spi_init(void) {
    DDRB |= (1 << PB2);  // SI output
    DDRB &= ~(1 << PB3); // SO input
    DDRB |= (1 << PB4);  // SCLK output
    DDRB |= (1 << PB1);  // CS output
    DDRB &= ~(1 << PB0); // GDO0 input

    SCK_off;
    MO_off;
    CS_on;
}

void spi_write(uint8_t command) {
    SCK_off; //SCK start low
    MO_off;

    uint8_t n = 8;
    while (n--) {
        if (command & 0x80) {
            MO_on;
        } else {
            MO_off;
        }

        SCK_on;
        NOP();
        SCK_off;

        command = command << 1;
    }

    MO_on;
}

uint8_t spi_read(void) {
    uint8_t result = 0;

    for (uint8_t i = 0; i < 8; i++) {
        if (MI_1) {
            result = (result << 1) | 0x01;
        } else {
            result = result << 1;
        }

        SCK_on;
        NOP();
        SCK_off;
        NOP();
    }

    return result;
}