Fix #249: add reentrancy protection in engineUpdate()

Author: terrillmoore

src/lmic/lmic.c

@@ -2453,8 +2453,9 @@ static void startRxPing (xref2osjob_t osjob) {
 #endif // !DISABLE_PING
 
 
-// Decide what to do next for the MAC layer of a device
-static void engineUpdate (void) {
+// Decide what to do next for the MAC layer of a device. Inner part.
+// Only called from outer part.
+static void engineUpdate_inner (void) {
 #if LMIC_DEBUG_LEVEL > 0
     LMIC_DEBUG_PRINTF("%"LMIC_PRId_ostime_t": engineUpdate, opmode=0x%x\n", os_getTime(), LMIC.opmode);
 #endif
@@ -2637,6 +2638,24 @@ static void engineUpdate (void) {
     os_setTimedCallback(&LMIC.osjob, txbeg-TX_RAMPUP, FUNC_ADDR(runEngineUpdate));
 }
 
+// Decide what to do next for the MAC layer of a device.
+// Outer part. Safe to call from anywhere; defers if it
+// detects a recursive call.
+static void engineUpdate (void) {
+    lmic_engine_update_state_t state;
+
+    state = LMIC.engineUpdateState;
+    if (state == lmic_EngineUpdateState_idle) {
+        LMIC.engineUpdateState = lmic_EngineUpdateState_busy;
+        do  {
+            engineUpdate_inner();
+            state = LMIC.engineUpdateState - 1;
+            LMIC.engineUpdateState = state;
+            } while (state != lmic_EngineUpdateState_idle);
+    } else {
+        LMIC.engineUpdateState = lmic_EngineUpdateState_again;
+    }
+}
 
 void LMIC_setAdrMode (bit_t enabled) {
     LMIC.adrEnabled = enabled ? FCT_ADREN : 0;

src/lmic/lmic.h

@@ -360,6 +360,14 @@ enum lmic_request_time_state_e {
 
 typedef u1_t lmic_request_time_state_t;
 
+enum lmic_engine_update_state_e {
+    lmic_EngineUpdateState_idle = 0,    // engineUpdate is idle.
+    lmic_EngineUpdateState_busy = 1,    // engineUpdate is busy, but has not been reentered.
+    lmic_EngineUpdateState_again = 2,   // engineUpdate is busy, and has to be evaluated again.
+};
+
+typedef u1_t lmic_engine_update_state_t;
+
 /*
 
 Structure:  lmic_client_data_t
@@ -480,7 +488,6 @@ struct lmic_t {
 #endif
 
     /* (u)int16_t things */
-
     rps_t       rps;            // radio parameter selections: SF, BW, CodingRate, NoCrc, implicit hdr
     u2_t        opmode;         // engineUpdate() operating mode flags
     u2_t        devNonce;       // last generated nonce
@@ -494,6 +501,7 @@ struct lmic_t {
 #endif
 
     /* (u)int8_t things */
+    lmic_engine_update_state_t engineUpdateState;   // state of the engineUpdate() evaluator.
     s1_t        rssi;
     s1_t        snr;            // LMIC.snr is SNR times 4
     u1_t        rxsyms;