Try-fix: L76K spamming bad times can crash nodes (#7261)

* Try-fix: Clear GPS buffer when we encounter a bad time in NMEA

* Fix signed int warnings

src/gps/GPS.cpp

@@ -1536,7 +1536,10 @@ The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of s
         if (t.tm_mon > -1) {
             LOG_DEBUG("NMEA GPS time %02d-%02d-%02d %02d:%02d:%02d age %d", d.year(), d.month(), t.tm_mday, t.tm_hour, t.tm_min,
                       t.tm_sec, ti.age());
-            perhapsSetRTC(RTCQualityGPS, t);
+            if (perhapsSetRTC(RTCQualityGPS, t) == RTCSetResultInvalidTime) {
+                // Clear the GPS buffer if we got an invalid time
+                clearBuffer();
+            }
             return true;
         } else
             return false;

src/gps/RTC.cpp

@@ -105,7 +105,7 @@ void readFromRTC()
  *
  * If we haven't yet set our RTC this boot, set it from a GPS derived time
  */
-bool perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate)
+RTCSetResult perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate)
 {
     static uint32_t lastSetMsec = 0;
     uint32_t now = millis();
@@ -113,7 +113,7 @@ bool perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate)
 #ifdef BUILD_EPOCH
     if (tv->tv_sec < BUILD_EPOCH) {
         LOG_WARN("Ignore time (%ld) before build epoch (%ld)!", printableEpoch, BUILD_EPOCH);
-        return false;
+        return RTCSetResultInvalidTime;
     }
 #endif
 
@@ -184,9 +184,9 @@ bool perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate)
         readFromRTC();
 #endif
 
-        return true;
+        return RTCSetResultSuccess;
     } else {
-        return false;
+        return RTCSetResultNotSet; // RTC was already set with a higher quality time
     }
 }
 
@@ -215,7 +215,7 @@ const char *RtcName(RTCQuality quality)
  * @param t The time to potentially set the RTC to.
  * @return True if the RTC was set to the provided time, false otherwise.
  */
-bool perhapsSetRTC(RTCQuality q, struct tm &t)
+RTCSetResult perhapsSetRTC(RTCQuality q, struct tm &t)
 {
     /* Convert to unix time
     The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970
@@ -231,7 +231,7 @@ bool perhapsSetRTC(RTCQuality q, struct tm &t)
     // LOG_DEBUG("Got time from GPS month=%d, year=%d, unixtime=%ld", t.tm_mon, t.tm_year, tv.tv_sec);
     if (t.tm_year < 0 || t.tm_year >= 300) {
         // LOG_DEBUG("Ignore invalid GPS month=%d, year=%d, unixtime=%ld", t.tm_mon, t.tm_year, tv.tv_sec);
-        return false;
+        return RTCSetResultInvalidTime;
     } else {
         return perhapsSetRTC(q, &tv);
     }

src/gps/RTC.h

@@ -22,13 +22,22 @@ enum RTCQuality {
     RTCQualityGPS = 4
 };
 
+/// The RTC set result codes
+/// Used to indicate the result of an attempt to set the RTC.
+enum RTCSetResult {
+    RTCSetResultNotSet = 0,      ///< RTC was set successfully
+    RTCSetResultSuccess = 1,     ///< RTC was set successfully
+    RTCSetResultInvalidTime = 3, ///< The provided time was invalid (e.g., before the build epoch)
+    RTCSetResultError = 4        ///< An error occurred while setting the RTC
+};
+
 RTCQuality getRTCQuality();
 
 extern uint32_t lastSetFromPhoneNtpOrGps;
 
 /// If we haven't yet set our RTC this boot, set it from a GPS derived time
-bool perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate = false);
-bool perhapsSetRTC(RTCQuality q, struct tm &t);
+RTCSetResult perhapsSetRTC(RTCQuality q, const struct timeval *tv, bool forceUpdate = false);
+RTCSetResult perhapsSetRTC(RTCQuality q, struct tm &t);
 
 /// Return a string name for the quality
 const char *RtcName(RTCQuality quality);