Improve NEC reading code

Now the NEC reading code is more cautious about what it accepts, more
readily throwing away input if anything odd is read.  It also, and this
is the big one, sends an event as soon as it's read all 32 bits, so I
can actually read short button presses now(!).  I'm not aware of any
major reliability problems left, so I'm leaving the translator by the TV
for now.

src/main.c

  */
 #define NEC_START_PULSE 45
 #define NEC_END_PULSE 405
-#define NEC_RPT_CMD_PULSE 959
+#define NEC_RPT_CMD_PULSE 962
 #define NEC_ZERO_PULSE 6
 #define NEC_ONE_PULSE 17
 #define NEC_COMMA_PULSE 23
 
 
 /*
- * Variables for holding the most recently read information from icuwidthcb
+ * Variables for holding the most recently read information from nec_icuwidthcb
  */
 static uint8_t nec_addr, nec_data;
 static bool nec_repeat = false;
 /*
  * ICU pulse width callback for reading NEC remote control frames
  */
-static void icuwidthcb(ICUDriver *icup)
+static void nec_icuwidthcb(ICUDriver *icup)
 {
     static int32_t index = -1;
-    static bool START_OCCURED = false;
+    static bool start_occured = false;
     static uint32_t tmp;
 
     icucnt_t cnt = icuGetWidthX(icup);
     if (CLOSE_TO(cnt, NEC_START_PULSE, NEC_DELTA)) {
         index = 0;
-        START_OCCURED = true;
+        start_occured = true;
     } else if (CLOSE_TO(cnt, NEC_ONE_PULSE, NEC_DELTA)) {
-        tmp |= 1 << (31 - index);
-        index++;
+        if (index > -1) {
+            tmp |= 1 << (31 - index);
+            index++;
+        }
     } else if (CLOSE_TO(cnt, NEC_ZERO_PULSE, NEC_DELTA)) {
-        tmp &= ~(1 << (31 - index));
-        index++;
-    } else if (CLOSE_TO(cnt, NEC_END_PULSE, 4*NEC_DELTA)) {
-        if ((START_OCCURED) && (index == 32)) {
-            nec_addr = (tmp >> 24) & 0xFF;
-            nec_data = (tmp >> 8) & 0xFF;
-        } else {
-            nec_addr = 0;
-            nec_data = 0;
+        if (index > -1) {
+            tmp &= ~(1 << (31 - index));
+            index++;
         }
+    } else if (CLOSE_TO(cnt, NEC_END_PULSE, 4*NEC_DELTA)) {
+        /* Nothing to do here */
+    } else if (CLOSE_TO(cnt, NEC_RPT_CMD_PULSE, 9*NEC_DELTA)) {
+        /* Nothing to do here */
+    } else if (CLOSE_TO(cnt, NEC_COMMA_PULSE, NEC_DELTA)) {
+        nec_repeat = true;
+        chEvtBroadcastFlags(&IR_receiver, 0);
+    } else {
+        /* When an unknown symbol is seen, forget what we've read */
+        nec_addr = 0;
+        nec_data = 0;
         nec_repeat = false;
-        START_OCCURED = false;
+        start_occured = false;
+        index = -1;
+    }
+
+    /* If we've read a whole message, send it on */
+    if (start_occured && index == 32) {
+        nec_addr = (tmp >> 24) & 0xFF;
+        nec_data = (tmp >> 8) & 0xFF;
+        nec_repeat = false;
+        start_occured = false;
         index = -1;
-    } else if (CLOSE_TO(cnt, NEC_RPT_CMD_PULSE, NEC_DELTA)) {
-        nec_repeat = true;
-    } else if (CLOSE_TO(cnt, NEC_COMMA_PULSE, NEC_DELTA)) {
         chEvtBroadcastFlags(&IR_receiver, 0);
     }
 }
 static ICUConfig icucfg = {
     ICU_INPUT_ACTIVE_HIGH,
     10000,            /* 10kHz ICU clock frequency. */
-    icuwidthcb,
+    nec_icuwidthcb,
     NULL,
     NULL,
     ICU_CHANNEL_1,
     /* Send a continuous stream of power off signals to the TV */
     while (true) {
         if (nec_addr == 0x80 && nec_data == 0x18) {
+            palClearPad(GPIOC, GPIOC_LED);
             if (chEvtWaitAnyTimeout(ALL_EVENTS, MS2ST(200))) {
                 continue;
             }
-            palClearPad(GPIOC, GPIOC_LED);
             for (int i = 0; i < 3; i++) {
                 rc5_frame(false, 0x00, 0x0C);
                 chThdSleepMilliseconds(90);