More GPS work (#2711)

Increase GPS buffer on esp32
Check for and flush GPS buffer when overfilled and corrupted.

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

arch/esp32/esp32.ini

@@ -30,6 +30,7 @@ build_flags =
   -DCONFIG_BT_NIMBLE_MAX_CCCDS=20
   -DCONFIG_BT_NIMBLE_HOST_TASK_STACK_SIZE=5120
   -DESP_OPENSSL_SUPPRESS_LEGACY_WARNING
+  -DSERIAL_BUFFER_SIZE=4096
   ;-DDEBUG_HEAP
 
 lib_deps =

src/gps/GPS.cpp

@@ -174,7 +174,7 @@ bool GPS::setupGPS()
 
 #ifdef ARCH_ESP32
         // In esp32 framework, setRxBufferSize needs to be initialized before Serial
-        _serial_gps->setRxBufferSize(2048); // the default is 256
+        _serial_gps->setRxBufferSize(SERIAL_BUFFER_SIZE); // the default is 256
 #endif
 
         // if the overrides are not dialled in, set them from the board definitions, if they exist
@@ -834,6 +834,14 @@ void GPS::forceWake(bool on)
     }
 }
 
+// clear the GPS rx buffer as quickly as possible
+void GPS::clearBuffer()
+{
+    int x = _serial_gps->available();
+    while (x--)
+        _serial_gps->read();
+}
+
 /// Prepare the GPS for the cpu entering deep or light sleep, expect to be gone for at least 100s of msecs
 int GPS::prepareSleep(void *unused)
 {

src/gps/GPS.h

@@ -91,6 +91,9 @@ class GPS : private concurrency::OSThread
     // Some GPS modules (ublock) require factory reset
     virtual bool factoryReset() { return true; }
 
+    // Empty the input buffer as quickly as possible
+    void clearBuffer();
+
   protected:
     /// Do gps chipset specific init, return true for success
     virtual bool setupGPS();

src/gps/NMEAGPS.cpp

@@ -253,8 +253,14 @@ bool NMEAGPS::hasFlow()
 bool NMEAGPS::whileIdle()
 {
     bool isValid = false;
+#ifdef SERIAL_BUFFER_SIZE
+    if (_serial_gps->available() >= SERIAL_BUFFER_SIZE - 1) {
+        LOG_WARN("GPS Buffer full with %u bytes waiting. Flushing to avoid corruption.\n", _serial_gps->available());
+        clearBuffer();
+    }
+#endif
     // if (_serial_gps->available() > 0)
-    // LOG_DEBUG("GPS Bytes Waiting: %u\n", _serial_gps->available());
+    LOG_DEBUG("GPS Bytes Waiting: %u\n", _serial_gps->available());
     // First consume any chars that have piled up at the receiver
     while (_serial_gps->available() > 0) {
         int c = _serial_gps->read();