Adding check for ongoing automatic-uplink

Before going after an automatic uplink, we should check if there was an
automatic uplink already ongoing, i.e., the ack for the previous
automatic uplink cycle has not been received.
If there is we shouldn't queue the new automatic uplink and wait for
the previous Ack cycle to complete.

Author: Hasnain Virk

features/lorawan/LoRaWANStack.cpp

@@ -691,7 +691,8 @@ void LoRaWANStack::process_reception(const uint8_t *const payload, uint16_t size
         state_machine_run_to_completion();
     }
 
-    if (_loramac.get_mlme_indication()->pending) {
+    // suppress auto uplink if another auto-uplink is in AWAITING_ACK state
+    if (_loramac.get_mlme_indication()->pending && !_automatic_uplink_ongoing) {
         tr_debug("MLME Indication pending");
         _loramac.post_process_mlme_ind();
         tr_debug("Immediate Uplink requested");
@@ -1027,11 +1028,15 @@ void LoRaWANStack::mcps_indication_handler()
             || (_loramac.get_device_class() == CLASS_C
                     && mcps_indication->type == MCPS_CONFIRMED)) {
 #if (MBED_CONF_LORA_AUTOMATIC_UPLINK_MESSAGE)
-        tr_debug("Sending empty uplink message...");
-        _automatic_uplink_ongoing = true;
-        const int ret = _queue->call(this, &LoRaWANStack::send_automatic_uplink_message, mcps_indication->port);
-        MBED_ASSERT(ret != 0);
-        (void)ret;
+            // Do not queue an automatic uplink of there is one already outgoing
+            // This means we have not received an ack for the previous automatic uplink
+            if (!_automatic_uplink_ongoing) {
+                tr_debug("Sending empty uplink message...");
+                _automatic_uplink_ongoing = true;
+                const int ret = _queue->call(this, &LoRaWANStack::send_automatic_uplink_message, mcps_indication->port);
+                MBED_ASSERT(ret != 0);
+                (void)ret;
+            }
 #else
         send_event_to_application(UPLINK_REQUIRED);
 #endif