/**
 * \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);
}

/* FORCE ERASE */
uint8_t send_cmd42_erase(){
        uint8_t response,i;
        uint8_t arg = 0x08;
        uint8_t command = 0x2a;
        uint16_t crc = calc_crc(mess,((command&arg)|command),CRC16STARTBIT);
        /* wait some clock cycles */
        sd_raw_rec_byte();
        Serial.print("Starting erase procedure");
        select_card(); // select SD card first

        sd_raw_send_byte(0x40 | 0x10);
        sd_raw_send_byte(0x01 & 0xff);
        sd_raw_send_byte(0x40 | 0x2a);
        sd_raw_send_byte((arg >> 0) & 0xff);
        /*CRC16 CCITT*/
        //CRC16 is calculated over data given/sent (block length*n_frames_sent)
        //SPI does not force CRC checking, but i'll enable it anyway
        //CRC16=size(command+argument) (38 bits)
        sd_raw_send_byte((crc >> 8) & 0xff);
        sd_raw_send_byte((crc >> 0) & 0xff);

        /* receive response */
        for(i = 0; i < 10; ++i)
        {
            response = sd_raw_rec_byte();
            if(response != 0xff)
                break;
        }

        return response;

}