uni-t-ut32x: use ASCII literals in packet parser, symbols for magic numbers

Slightly unobfuscate the UT32x packet parser. The protocol is mostly
ASCII based, checks for hex numbers may be unexpected. Use symbolic
identifiers for the packet length and some special characters.

diff --git a/src/hardware/uni-t-ut32x/protocol.c b/src/hardware/uni-t-ut32x/protocol.c
index 1d4324b32a539e2dbd7ff7aba075b046e4a5d7a0..85752419df24b748be888292071a1ca2b104f14d 100644 (file)
--- a/src/hardware/uni-t-ut32x/protocol.c
+++ b/src/hardware/uni-t-ut32x/protocol.c
@@ -22,6 +22,14 @@
 #include <math.h>
 #include "protocol.h"
 
+#define SEP    "\r\n"
+#define BLANK  ':'
+#define NEG    ';'
+
+/*
+ * Get a temperature value from a four-character buffer. The value is
+ * encoded in ASCII and the unit is deci-degrees (tenths of degrees).
+ */
 static float parse_temperature(unsigned char *buf)
 {
        float temp;
@@ -31,23 +39,22 @@ static float parse_temperature(unsigned char *buf)
        negative = FALSE;
        temp = 0.0;
        for (i = 0; i < 4; i++) {
-               if (buf[i] == 0x3a)
+               if (buf[i] == BLANK)
                        continue;
-               if (buf[i] == 0x3b) {
+               if (buf[i] == NEG) {
                        if (negative) {
                                sr_dbg("Double negative sign!");
                                return NAN;
-                       } else {
-                               negative = TRUE;
-                               continue;
                        }
+                       negative = TRUE;
+                       continue;
                }
-               if (buf[i] < 0x30 || buf[i] > 0x39) {
+               if (buf[i] < '0' || buf[i] > '9') {
                        sr_dbg("Invalid digit '%.2x'!", buf[i]);
                        return NAN;
                }
                temp *= 10;
-               temp += (buf[i] - 0x30);
+               temp += buf[i] - '0';
        }
        temp /= 10;
        if (negative)
@@ -80,8 +87,8 @@ static void process_packet(struct sr_dev_inst *sdi)
        }
 
        is_valid = TRUE;
-       if (devc->packet[1] == 0x3b && devc->packet[2] == 0x3b
-                       && devc->packet[3] == 0x3b && devc->packet[4] == 0x3b)
+       if (devc->packet[1] == NEG && devc->packet[2] == NEG
+                       && devc->packet[3] == NEG && devc->packet[4] == NEG)
                /* No measurement: missing channel, empty storage location, ... */
                is_valid = FALSE;
 
@@ -93,7 +100,7 @@ static void process_packet(struct sr_dev_inst *sdi)
                sr_analog_init(&analog, &encoding, &meaning, &spec, 1);
                analog.meaning->mq = SR_MQ_TEMPERATURE;
                analog.meaning->mqflags = 0;
-               switch (devc->packet[5] - 0x30) {
+               switch (devc->packet[5] - '0') {
                case 1:
                        analog.meaning->unit = SR_UNIT_CELSIUS;
                        break;
@@ -107,7 +114,7 @@ static void process_packet(struct sr_dev_inst *sdi)
                        /* We can still pass on the measurement, whatever it is. */
                        sr_dbg("Unknown unit 0x%.2x.", devc->packet[5]);
                }
-               switch (devc->packet[13] - 0x30) {
+               switch (devc->packet[13] - '0') {
                case 0:
                        /* Channel T1. */
                        analog.meaning->channels = g_slist_append(NULL, g_slist_nth_data(sdi->channels, 0));
@@ -162,14 +169,14 @@ SR_PRIV void LIBUSB_CALL uni_t_ut32x_receive_transfer(struct libusb_transfer *tr
                                hid_payload_len);
                devc->packet_len += hid_payload_len;
                if (devc->packet_len >= 2
-                               && devc->packet[devc->packet_len - 2] == 0x0d
-                               && devc->packet[devc->packet_len - 1] == 0x0a) {
+                               && 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? */
-                       if (devc->packet_len == 19)
+                       if (devc->packet_len == PACKET_SIZE)
                                process_packet(sdi);
                        /* Either way, done with it. */
                        devc->packet_len = 0;
-               } else if (devc->packet_len > 19) {
+               } else if (devc->packet_len > PACKET_SIZE) {
                        /* Guard against garbage from the device overrunning
                         * our packet buffer. */
                        sr_dbg("Buffer overrun!");

diff --git a/src/hardware/uni-t-ut32x/protocol.h b/src/hardware/uni-t-ut32x/protocol.h
index acc453ec170d34752c0017d761022817cc245c72..f30ff2b711d995d46b91c460a1530a412d423d2e 100644 (file)
--- a/src/hardware/uni-t-ut32x/protocol.h
+++ b/src/hardware/uni-t-ut32x/protocol.h
@@ -35,6 +35,8 @@
 #define EP_IN (0x80 | 2)
 #define EP_OUT 2
 
+#define PACKET_SIZE    19
+
 enum ut32x_data_source {
        DATA_SOURCE_LIVE,
        DATA_SOURCE_MEMORY,