test_spi.c

void SPI_Init(void){

   /* Set !DM, MOSI and SCK output, MISO input */

   DDRB |= (1<<PB3) | (1<<PB5) | (1<<PB7);

   DDRB &= ~(1<<PB6);

   /* Enable SPI, Master, set clock rate fck/16 */

   SPCR = (1<<SPE) | (1<<MSTR) | (1<<SPR0);

}

void SPI_Transmit(uint8_t cData){

   /* Start transmission */

   SPDR = cData;

   /* Wait for transmission complete */

   while (!(SPSR & (1<<SPIF)))

      printf("waiting\n");

}

void main(){

   SPI_Init();

   while (1){

      printf("sende jetzt\n");

      SPI_Transmit(164);

      printf("senden fertig\n");

   }

}