PDC_PKT_CLEAR_BSY
buf[14] = (1 << 5) | ATA_REG_DEVICE | PDC_PKT_CLEAR_BSY;
buf[12] = (1 << 5) | PDC_PKT_CLEAR_BSY | ATA_REG_DEVICE;
buf[i++] = (1 << 5) | PDC_PKT_CLEAR_BSY | ATA_REG_DEVICE;