uni-t-ut32x: improve robustness of packet parser, more diagnostics

Always print the data bytes of received buffers in the packet parser,
then check some more fixed fields to not process invalid packets, then
process the packet content as the previous implementation did.

Call the packet parser for incomplete packets and discarded input
buffers as well (initial synchronization, re-sync after comm errors).
This results in the availability of more diagnostics during development.

Pass the packet's location and size from outside. This prepares the
logic to cope with situations where the receive buffer contains multiple
(potentially incomplete) packets.

src/hardware/uni-t-ut32x/protocol.c

@@ -63,7 +63,7 @@ static float parse_temperature(unsigned char *buf)
 	return temp;
 }
 
-static void process_packet(struct sr_dev_inst *sdi)
+static void process_packet(struct sr_dev_inst *sdi, uint8_t *pkt, size_t len)
 {
 	struct dev_context *devc;
 	struct sr_datafeed_packet packet;
@@ -73,34 +73,36 @@ static void process_packet(struct sr_dev_inst *sdi)
 	struct sr_analog_spec spec;
 	GString *spew;
 	float temp;
-	int i;
 	gboolean is_valid;
 
-	devc = sdi->priv;
-	sr_dbg("Received full 19-byte packet.");
 	if (sr_log_loglevel_get() >= SR_LOG_SPEW) {
-		spew = g_string_sized_new(60);
+		spew = sr_hexdump_new(pkt, len);
-		for (i = 0; i < devc->packet_len; i++)
+		sr_spew("Got a packet, len %zu, bytes%s", len, spew->str);
-			g_string_append_printf(spew, "%.2x ", devc->packet[i]);
+		sr_hexdump_free(spew);
-		sr_spew("%s", spew->str);
-		g_string_free(spew, TRUE);
 	}
+	if (len != PACKET_SIZE)
+		return;
+	if (pkt[17] != SEP[0] || pkt[18] != SEP[1])
+		return;
+	if (pkt[8] != '0' || pkt[16] != '1')
+		return;
+	sr_dbg("Processing 19-byte packet.");
 
 	is_valid = TRUE;
-	if (devc->packet[1] == NEG && devc->packet[2] == NEG
+	if (pkt[1] == NEG && pkt[2] == NEG && pkt[3] == NEG && pkt[4] == NEG)
-			&& devc->packet[3] == NEG && devc->packet[4] == NEG)
 		/* No measurement: missing channel, empty storage location, ... */
 		is_valid = FALSE;
 
-	temp = parse_temperature(devc->packet + 1);
+	temp = parse_temperature(&pkt[1]);
 	if (isnan(temp))
 		is_valid = FALSE;
 
 	if (is_valid) {
+		memset(&packet, 0, sizeof(packet));
 		sr_analog_init(&analog, &encoding, &meaning, &spec, 1);
 		analog.meaning->mq = SR_MQ_TEMPERATURE;
 		analog.meaning->mqflags = 0;
-		switch (devc->packet[5] - '0') {
+		switch (pkt[5] - '0') {
 		case 1:
 			analog.meaning->unit = SR_UNIT_CELSIUS;
 			break;
@@ -112,9 +114,9 @@ static void process_packet(struct sr_dev_inst *sdi)
 			break;
 		default:
 			/* We can still pass on the measurement, whatever it is. */
-			sr_dbg("Unknown unit 0x%.2x.", devc->packet[5]);
+			sr_dbg("Unknown unit 0x%.2x.", pkt[5]);
 		}
-		switch (devc->packet[13] - '0') {
+		switch (pkt[13] - '0') {
 		case 0:
 			/* Channel T1. */
 			analog.meaning->channels = g_slist_append(NULL, g_slist_nth_data(sdi->channels, 0));
@@ -130,7 +132,7 @@ static void process_packet(struct sr_dev_inst *sdi)
 			analog.meaning->mqflags |= SR_MQFLAG_RELATIVE;
 			break;
 		default:
-			sr_err("Unknown channel 0x%.2x.", devc->packet[13]);
+			sr_err("Unknown channel 0x%.2x.", pkt[13]);
 			is_valid = FALSE;
 		}
 		if (is_valid) {
@@ -148,6 +150,7 @@ static void process_packet(struct sr_dev_inst *sdi)
 	 * a sample limit on "Memory" data source still works: Unused
 	 * memory slots come through as "----" measurements.
 	 */
+	devc = sdi->priv;
 	sr_sw_limits_update_samples_read(&devc->limits, 1);
 	if (sr_sw_limits_check(&devc->limits))
 		sr_dev_acquisition_stop(sdi);
@@ -171,15 +174,14 @@ SR_PRIV void LIBUSB_CALL uni_t_ut32x_receive_transfer(struct libusb_transfer *tr
 		if (devc->packet_len >= 2
 				&& devc->packet[devc->packet_len - 2] == SEP[0]
 				&& devc->packet[devc->packet_len - 1] == SEP[1]) {
-			/* Got end of packet, but do we have a complete packet? */
+			/* Got end of packet. */
-			if (devc->packet_len == PACKET_SIZE)
+			process_packet(sdi, devc->packet, devc->packet_len);
-				process_packet(sdi);
-			/* Either way, done with it. */
 			devc->packet_len = 0;
 		} else if (devc->packet_len > PACKET_SIZE) {
 			/* Guard against garbage from the device overrunning
 			 * our packet buffer. */
 			sr_dbg("Buffer overrun!");
+			process_packet(sdi, devc->packet, devc->packet_len);
 			devc->packet_len = 0;
 		}
 	}

src/hardware/uni-t-ut32x/protocol.h

@@ -55,7 +55,7 @@ struct dev_context {
 	struct libusb_transfer *xfer;
 
 	unsigned char packet[32];
-	int packet_len;
+	size_t packet_len;
 };
 
 SR_PRIV int uni_t_ut32x_handle_events(int fd, int revents, void *cb_data);