slip binary IO in C

host_slip.c

int main(int argc, char const *argv[]) {
	
	g_fd = 0x00;
	struct response *resp;
	struct timer_data *data;
	uint8_t buff[8] = {0x00};
	uint16_t crc = 0x00;

	if (argc <= 3) {
		fprintf(stderr, "host_slip <prescaler> <ocr> <st_max>\n");
		return -1;
	}

	if (0 > (g_fd = open(SERIAL_PORT, O_RDWR | O_NOCTTY | O_SYNC))) {
		fprintf(stderr, "Unable to open device [%s]\n", SERIAL_PORT);
		return 0;
	}

	tty_attrib_conf(g_fd, BAUD_9600, 0);
	tty_block_conf(g_fd, 1);

	data = (struct timer_data *)buff;

	data->crc16 = 0x0000;
	data->prescaler = atoi(argv[1]);
	data->ocr = atoi(argv[2]);
	data->st_max = atoi(argv[3]);

	// insert the CRC
	crc = crc16(0x00, buff, sizeof(struct timer_data));
	data->crc16 = crc;

	// wait for the board to reset itself
	sleep(4);

	printf("Sending: %d/%d/%d, CRC: 0x%04x\n", 
			data->prescaler,
			data->ocr,
			data->st_max,
			data->crc16);

	slip_send(buff, sizeof(struct timer_data));
	slip_recv(buff, sizeof(buff));

	resp = (struct response *)buff;

	// zero the CRC to perform verification
	buff[6] = buff[0];
	buff[7] = buff[1];
	buff[0] = 0x00;
	buff[1] = 0x00;

	// we've got the calculated CRC now
	crc = crc16(0x00, buff, sizeof(struct response));

	// restore the CRC
	buff[0] = buff[6];
	buff[1] = buff[7];

	printf("CRC/CRC_CALCD/STATUS: 0x%04x/0x%04x/%s\n", 
			resp->crc16, 
			crc,
			(resp->status == 0x10 ? "ACK" : "NACK"));

	close(g_fd);

	return 0;
}