Fix false RX loss detection on EEPROM read/write

The problem is caused by hardware counters (timekeeping and PPM/PWM
measurement) that keep running while the firmware is frozen. The result
is misinterpretation of received data.

EEPROM read & write now call a suspend and resume function to make RX
ignore incoming wrong data during reads/writes (and flush the wrong data
on resume).

Fixes issue #1257

(+1 squashed commit)
- Moved the check for skipSamples to the right place.

As commented by hydra

src/main/config/config.c

@@ -829,6 +829,8 @@ void readEEPROM(void)
     if (!isEEPROMContentValid())
         failureMode(10);
 
+    suspendRxSignal();
+
     // Read flash
     memcpy(&masterConfig, (char *) CONFIG_START_FLASH_ADDRESS, sizeof(master_t));
 
@@ -844,6 +846,8 @@ void readEEPROM(void)
 
     validateAndFixConfig();
     activateConfig();
+
+    resumeRxSignal();
 }
 
 void readEEPROMAndNotify(void)
@@ -862,6 +866,8 @@ void writeEEPROM(void)
     uint32_t wordOffset;
     int8_t attemptsRemaining = 3;
 
+    suspendRxSignal();
+
     // prepare checksum/version constants
     masterConfig.version = EEPROM_CONF_VERSION;
     masterConfig.size = sizeof(master_t);
@@ -903,6 +909,8 @@ void writeEEPROM(void)
     if (status != FLASH_COMPLETE || !isEEPROMContentValid()) {
         failureMode(10);
     }
+
+    resumeRxSignal();
 }
 
 void ensureEEPROMContainsValidData(void)

src/main/rx/rx.c

@@ -71,6 +71,7 @@ static bool rxFlightChannelsValid = false;
 
 static uint32_t rxUpdateAt = 0;
 static uint32_t needRxSignalBefore = 0;
+static uint8_t  skipRxSamples = 0;
 
 int16_t rcRaw[MAX_SUPPORTED_RC_CHANNEL_COUNT];     // interval [1000;2000]
 int16_t rcData[MAX_SUPPORTED_RC_CHANNEL_COUNT];     // interval [1000;2000]
@@ -79,6 +80,8 @@ int16_t rcData[MAX_SUPPORTED_RC_CHANNEL_COUNT];     // interval [1000;2000]
 
 #define DELAY_50_HZ (1000000 / 50)
 #define DELAY_10_HZ (1000000 / 10)
+#define SKIP_RC_SAMPLES_ON_SUSPEND 75               // approx. 1.5 seconds of samples at 50Hz
+#define SKIP_RC_SAMPLES_ON_RESUME  2                // flush 2 samples to drop wrong measurements
 
 rxRuntimeConfig_t rxRuntimeConfig;
 static rxConfig_t *rxConfig;
@@ -261,6 +264,16 @@ static void resetRxSignalReceivedFlagIfNeeded(uint32_t currentTime)
     }
 }
 
+void suspendRxSignal(void)
+{
+    skipRxSamples = SKIP_RC_SAMPLES_ON_SUSPEND;
+}
+
+void resumeRxSignal(void)
+{
+    skipRxSamples = SKIP_RC_SAMPLES_ON_RESUME;
+}
+
 void updateRx(uint32_t currentTime)
 {
     resetRxSignalReceivedFlagIfNeeded(currentTime);
@@ -467,6 +480,11 @@ void calculateRxChannelsAndUpdateFailsafe(uint32_t currentTime)
         }
     }
 
+    if (skipRxSamples) {
+        skipRxSamples--;
+        return;
+    }
+
     readRxChannelsApplyRanges();
     detectAndApplySignalLossBehaviour();
 

src/main/rx/rx.h

@@ -142,3 +142,5 @@ uint8_t serialRxFrameStatus(rxConfig_t *rxConfig);
 void updateRSSI(uint32_t currentTime);
 void resetAllRxChannelRangeConfigurations(rxChannelRangeConfiguration_t *rxChannelRangeConfiguration);
 
+void suspendRxSignal(void);
+void resumeRxSignal(void);