Fix random RX loss beep when using Serial RX receivers.

src/main/flight/failsafe.c

@@ -18,6 +18,8 @@
 #include <stdbool.h>
 #include <stdint.h>
 
+#include "debug.h"
+
 #include "common/axis.h"
 
 #include "rx/rx.h"
@@ -75,11 +77,11 @@ failsafePhase_e failsafePhase()
     return failsafeState.phase;
 }
 
-#define MAX_COUNTER_VALUE_WHEN_RX_IS_RECEIVED_AFTER_RX_CYCLE 1
+#define FAILSAFE_COUNTER_THRESHOLD 20
 
 bool failsafeIsReceivingRxData(void)
 {
-    return failsafeState.counter <= MAX_COUNTER_VALUE_WHEN_RX_IS_RECEIVED_AFTER_RX_CYCLE;
+    return failsafeState.counter <= FAILSAFE_COUNTER_THRESHOLD;
 }
 
 bool failsafeIsMonitoring(void)
@@ -130,8 +132,8 @@ static void failsafeApplyControlInput(void)
 
 void failsafeOnValidDataReceived(void)
 {
-    if (failsafeState.counter > 20)
+    if (failsafeState.counter > FAILSAFE_COUNTER_THRESHOLD)
-        failsafeState.counter -= 20;
+        failsafeState.counter -= FAILSAFE_COUNTER_THRESHOLD;
     else
         failsafeState.counter = 0;
 }

src/main/rx/rx.c

@@ -225,6 +225,9 @@ void updateRx(uint32_t currentTime)
     if (rxSignalReceived) {
         if (((int32_t)(currentTime - needRxSignalBefore) >= 0)) {
             rxSignalReceived = false;
+#ifdef DEBUG_RX_SIGNAL_LOSS
+            debug[0]++;
+#endif
         }
     }
 

src/test/unit/flight_failsafe_unittest.cc

@@ -176,22 +176,27 @@ TEST(FlightFailsafeTest, TestFailsafeDetectsRxLossAndStartsLanding)
     // given
     ENABLE_ARMING_FLAG(ARMED);
 
-    // when
-    failsafeOnRxCycleStarted();
-    // no call to failsafeOnValidDataReceived();
-
-    failsafeUpdateState();
-
-    // then
-    EXPECT_EQ(false, failsafeIsActive());
-    EXPECT_EQ(FAILSAFE_IDLE, failsafePhase());
-
     //
-    // currently one cycle must occur (above) so that the next cycle (below) can detect the lack of an update.
+    // currently 20 cycles must occur before the lack of an update triggers RX loss detection.
     //
+    // FIXME see comments about RX_SERIAL/RX_MSP above, the test should likely deal with time rather than counters.
+    int failsafeCounterThreshold = 20;
 
     // when
-    for (int i = 0; i < FAILSAFE_UPDATE_HZ - 1; i++) {
+    for (int i = 0; i < failsafeCounterThreshold; i++) {
+
+        failsafeOnRxCycleStarted();
+        // no call to failsafeOnValidDataReceived();
+
+        failsafeUpdateState();
+
+        // then
+        EXPECT_EQ(FAILSAFE_IDLE, failsafePhase());
+        EXPECT_EQ(false, failsafeIsActive());
+    }
+
+    // when
+    for (int i = 0; i < FAILSAFE_UPDATE_HZ - failsafeCounterThreshold; i++) {
 
         failsafeOnRxCycleStarted();
         // no call to failsafeOnValidDataReceived();
@@ -201,7 +206,6 @@ TEST(FlightFailsafeTest, TestFailsafeDetectsRxLossAndStartsLanding)
         // then
         EXPECT_EQ(FAILSAFE_RX_LOSS_DETECTED, failsafePhase());
         EXPECT_EQ(false, failsafeIsActive());
-
     }
 
     //
@@ -305,6 +309,7 @@ TEST(FlightFailsafeTest, TestFailsafeNotActivatedWhenDisarmedAndRXLossIsDetected
 extern "C" {
 int16_t rcData[MAX_SUPPORTED_RC_CHANNEL_COUNT];
 uint8_t armingFlags;
+int16_t debug[DEBUG16_VALUE_COUNT];
 
 void delay(uint32_t) {}
 
@@ -316,6 +321,8 @@ void mwDisarm(void) {
     callCounts[COUNTER_MW_DISARM]++;
 }
 
-void beeper(beeperMode_e mode) { }
+void beeper(beeperMode_e mode) {
+    UNUSED(mode);
+}
 
 }