Hat jemand für den ATtiny44 eine funktionierende USI to SPI Routine?

#include <avr\io.h>

struct bits {

  uint8_t b0:1;

  uint8_t b1:1;

  uint8_t b2:1;

  uint8_t b3:1;

  uint8_t b4:1;

  uint8_t b5:1;

  uint8_t b6:1;

  uint8_t b7:1;

} __attribute__((__packed__));

#define SBIT(port,pin) ((*(volatile struct bits*)&port).b##pin)

#define SPI_CLK         SBIT( PORTB, 0 )        // clock

#define SPI_CLK_DDR     SBIT( DDRB,  0 )

#define SPI_MISO_PIN    SBIT( PINB,  2 )

#define HC165_LD        SBIT( PORTB, 3 )

#define HC165_LD_DDR    SBIT( DDRB,  3 )

#define SPI_MOSI        SBIT( PORTB, 1 )

uint8_t spi_io( uint8_t val )

{

  uint8_t i;

  for( i = 8; i; i-- ){

    SPI_MOSI = 0;

    if( val & 0x80 )

      SPI_MOSI = 1;

    val <<= 1;

    if( SPI_MISO_PIN )

      val += 1;

    SPI_CLK = 0;

    SPI_CLK = 1;

  }

  return val;

}

#include <avr/io.h>

#include <stdlib.h>

#include <avr/interrupt.h>

#include <util/delay.h>

void SPI_init(void)

{

  DDRA  |=  (1<<PA4)|(1<<PA5);   //Output:   PA4=USCK, PA5=DO

  DDRB  |=  (1<<PB1);      //Output:   PB1=CS

  DDRA  &=  !(1<<PA6);      //Input:   PA6=DI

  PORTA  |=  (1<<PA6);      //int. Pull-up an PA6 aktivieren

  DDRA   |=   (1<<PA7);      //LED auf Ausgang

  USICR   =   (1<<USIWM0) | (1<<USICLK)| (1<<USITC)| (1<<USICS1);

}

void SPI_transfer(int data)

{

    PORTB  &=  !(1<<PB1);    //CS = 0

    USIDR = data;        //Daten in Data Register laden

    USISR   |=  (1<<USIOIF);  //Überlaufflag löschen  

    while (!(USISR & (1<<USIOIF)))  //solange kein Timerüberlauf...

    {

      USICR  |=  (1<<USITC);    //Toggle clk

      USICR  |=  (1<<USITC);

    }

    PORTB  |=  (1<<PB1);    //CS = 1

}

int main (void)

{

  SPI_init();

  sei();

  while(1)

  {

    SPI_transfer(0xAF);

    PORTA |= (1<<PA7);  // Led on

    _delay_ms(1000);

    PORTA &= !(1<<PA7);  // Led off

    _delay_ms(1000);

  }

}