/**
 * \ingroup sd_raw
 * Sends a raw byte to the memory card.
 *
 * \param[in] b The byte to sent.
 * \see sd_raw_rec_byte
 */
void sd_raw_send_byte(uint8_t b)
{
    SPDR = b;
    /* wait for byte to be shifted out */
    while(!(SPSR & (1 << SPIF)));
    SPSR &= ~(1 << SPIF);
}

static  unsigned char  xchg(unsigned char  c)
{
    SPDR = c;
    while ((SPSR & (1<<SPIF)) == 0)  ;
    return  SPDR;
}


static int8_t  sd_wait_for_data(void)
{
    int16_t             i;
    uint8_t             r;

    for (i=0; i<100; i++)
    {
        r = xchg(0xff);
        if (r != 0xff)  break;
    }
    return  (int8_t) r;
}


static    uint8_t lock()
    {
        uint8_t response,i,r;
        uint32_t arg = 0x01020102;
        uint8_t command = 0x2a;
        uint16_t crc = calc_crc(mess,((command&arg)|command),CRC16STARTBIT);
        Serial.print("Starting lock procedure");
        select_card(); // select SD card first
        sd_raw_rec_byte();
        sd_raw_send_command(CMD_CRC_ON_OFF, 0);
        if(sd_raw_send_command(CMD_SET_BLOCKLEN, 4))
        {
                Serial.print("\nIMPOSIBLE TO SET_BLOCKLEN to 1 byte\n");
                unselect_card();
                return 0;
        }else{
                Serial.print("\nSET_BLOCKLEN to 1 byte\n");
        }
    xchg(0xfe);
    xchg(0x2a);
    sd_raw_send_byte((arg >> 24) & 0xff);
    sd_raw_send_byte((arg >> 16) & 0xff);
    sd_raw_send_byte((arg >> 8) & 0xff);
    sd_raw_send_byte((arg >> 0) & 0xff);
    /*xchg(arg)*/;
    xchg((crc >> 8) & 0xff);
    xchg((crc >> 0) & 0xff);
    xchg(0xff);
    r=sd_wait_for_data();
    Serial.println(r, BIN);

}