AVR clib boot_program_page schreibt nicht in Programflash

#include <inttypes.h>

#include <avr/interrupt.h>

#include <avr/pgmspace.h>

#include <stdlib.h>

#include <avr/io.h>

#include <avr/boot.h>

#define  NOP  asm volatile("nop"::);

// 1:1 aus libc    

void boot_program_page (uint32_t page, uint8_t *buf)

{

    uint16_t i;

    uint8_t sreg;

    // Disable interrupts.

    sreg = SREG;

    cli();

    eeprom_busy_wait ();

    boot_page_erase (page);

    boot_spm_busy_wait ();      // Wait until the memory is erased.

    for (i=0; i<SPM_PAGESIZE; i+=2)

    {

        // Set up little-endian word.

        uint16_t w = *buf++;

        w += (*buf++) << 8;

        boot_page_fill (page + i, w);

    }

    boot_page_write (page);     // Store buffer in flash page.

    boot_spm_busy_wait();       // Wait until the memory is written.

    // Reenable RWW-section again. We need this if we want to jump back

    // to the application after bootloading.

    boot_rww_enable ();

    // Re-enable interrupts (if they were ever enabled).

    SREG = sreg;

}

int main(void)

{

    uint32_t    flash_adr = 0;

    uint8_t     buf[SPM_PAGESIZE];

    // Puffer testweise mit irgendwas fuellen

    for(int n=0; n<SPM_PAGESIZE; n++)

    {

        buf[n] = 0x55;

    }

    // Flash Programmierung

    boot_program_page (flash_adr, buf);

    while (1) 

    {

        NOP;    // Haltepunkt -> im prog Flash sollte doch jetzt ab 

                // prog 0x000000 der Inhalt von buf[] stehen ??

    }

}