DRESULT disk_writep (const BYTE* buff, DWORD sc){
    static WORD wr_cnt;
    if(sd_blsize == 0xff) return RES_NOTRDY;

    if (!buff) {
        if (sc) {
            CS_LOW
            spi_io(0xff);
            spi_io(0xff);
            if(sd_blsize == 0x00) sc *= 512;
            spi_io(CMD_24);
            spi_io(((BYTE*) &sc)[3]);
            spi_io(((BYTE*) &sc)[2]);
            spi_io(((BYTE*) &sc)[1]);
            spi_io(((BYTE*) &sc)[0]);
            spi_io(0xff);
            if(in_oout() != 0X00) return RES_ERROR;
            spi_io(0xff);
            spi_io(0xfe);

            writep_status=1;
            wr_cnt = 512;
        } else {
            // Finalize write process
            if(writep_status == 0) return RES_NOTRDY;
            while(wr_cnt--){
                spi_io(0x00);
            }
            in_oout();
            while(spi_io(0xff) != 0xff);
            writep_status = 0x00;
            CS_HIGH
        }
    } else {
        if(writep_status == 0) return RES_NOTRDY;
        wr_cnt -= (WORD)sc;
            while(sc--){
                spi_io(*buff++);
            }
    }
    return RES_OK;
}