SPI master transfer for Atmega328p

// Example of Master Write SPI for Atmega328p
// SS(CE) <=> PB0
#include <avr/io.h>

#define bitSet(p,m) ((p) |= (m))
#define bitClear(p,m) ((p) &= ~(m))

void SPI_initMaster(void);
void SPI_transferByte(char data);

int main(void) {
    SPI_initMaster();
    bitClear(PORTB, 0);
    SPI_transferByte(0b01010101);
    bitSet(PORTB, 1);
}

void SPI_initMaster() {
    DDRB = (1 << 0) | (1 << 3) | (1 << 5);
    SPCR = (1 << SPE) | (1 << MSTR) | (1 << SPR0);
}

void SPI_transferByte(char data) {
    SPDR = data;
    while(!(SPSR & (1 << SPIF)))
      ;
}