Merge pull request #987 from mcci-catena/issue968

Fix hang after 8 hours with certain compilers

README.md

@@ -999,6 +999,10 @@ function uflt12f(rawUflt12)
 
 ## Release History
 
+- HEAD has the following changes.
+
+  - Work around different behavior for `int32_t` wrap in newer GCC versions. ([#968](https://github.com/mcci-catena/arduino-lmic/issues/968), `v5.0.1-pre1`)
+
 - v5.0.0 has the following changes.
 
   - Enable device time request by default in config file ([#840](https://github.com/mcci-catena/arduino-lmic/issues/840)).

src/lmic/lmic.c

@@ -2597,8 +2597,19 @@ static void engineUpdate_inner (void) {
             goto checkrx;
         }
 #endif // !DISABLE_BEACONS
-        // Earliest possible time vs overhead to setup radio
-        if( txbeg - (now + TX_RAMPUP) < 0 ) {
+
+        //
+        // Compare earliest possible time vs overhead to setup radio, and start
+        // transmit if we can. Otherwise (way below), if we're not tracking a
+        // beacon, we'll simply queue an osjob for the computed txbeg time.
+        //
+        // Per bug #968, the explicit cast to (ostime_t) is needed
+        // (with some versions of GCC) if txbeg is positive and now + TX_RAMPUP is negative
+        // otherwise the compiler falsely assumes that the computation
+        // is positive.
+        //
+        volatile ostime_t tdiff = txbeg - (now + TX_RAMPUP);
+        if( tdiff < 0 ) {
             // We could send right now!
             txbeg = now;
             dr_t txdr = (dr_t)LMIC.datarate;

src/lmic/lmic.h

@@ -106,7 +106,7 @@ extern "C"{
 	((((major)*UINT32_C(1)) << 24) | (((minor)*UINT32_C(1)) << 16) | (((patch)*UINT32_C(1)) << 8) | (((local)*UINT32_C(1)) << 0))
 
 #define	ARDUINO_LMIC_VERSION    \
-    ARDUINO_LMIC_VERSION_CALC(5, 0, 0, 0)  /* 5.0.0 */
+    ARDUINO_LMIC_VERSION_CALC(5, 0, 1, 1)  /* 5.0.1-pre1 */
 
 #define	ARDUINO_LMIC_VERSION_GET_MAJOR(v)	\
 	((((v)*UINT32_C(1)) >> 24u) & 0xFFu)