Merge pull request #3525 from oltaco/airoha-sleep

Use Airoha AG3335 backup mode sleep for faster GPS fix time

src/helpers/sensors/AirohaSleep.h

@@ -0,0 +1,19 @@
+#pragma once
+#include <helpers/sensors/LocationProvider.h>
+
+// Board must keep the GPS RTC backup pin powered and can cut GPS power once we return.
+// Returns true if the command was acked within 3 attempts, otherwise returns false.
+static inline bool airohaEnterSleep(LocationProvider* nmea) {
+  for (uint8_t attempt = 0; attempt < 3; attempt++) {
+    nmea->drain();
+    nmea->sendSentence("$PAIR650,0");
+    if (nmea->waitFor("$PAIR001,650,0", 50)) {  // wait for the command received signal
+      #ifdef GPS_NMEA_DEBUG
+      Serial.printf("Airoha RTC Backup sleep command accepted by GPS after %u attempts\r\n", attempt + 1);
+      #endif
+      nmea->waitFor("$PAIR650,0", 50); // give the GPS 50ms grace to signal it is ready for sleep
+      return true;
+    }
+  }
+  return false;
+}

src/helpers/sensors/LocationProvider.h

@@ -19,6 +19,8 @@ public:
     virtual bool isValid() = 0;
     virtual long getTimestamp() = 0;
     virtual void sendSentence(const char * sentence);
+    virtual bool waitFor(const char* prefix, uint32_t timeout_ms) { return false; }
+    virtual void drain() { }
     virtual void reset() = 0;
     virtual void begin() = 0;
     virtual void stop() = 0;

src/helpers/sensors/MicroNMEALocationProvider.h

@@ -173,10 +173,31 @@ public :
         return dt.unixtime();
     } 
 
+    void drain() { while (_gps_serial->available()) _gps_serial->read(); }
+
+    const char* getSentence() const { return nmea.getSentence(); }
+
     void sendSentence(const char *sentence) override {
         nmea.sendSentence(*_gps_serial, sentence);
     }
 
+    bool waitFor(const char* prefix, uint32_t timeout_ms) {
+        size_t plen = strlen(prefix);
+        uint32_t timeout = millis() + timeout_ms;
+        while ((int32_t)(millis() - timeout) < 0) {
+            if (_gps_serial->available()) {
+                char c = _gps_serial->read();
+                #ifdef GPS_NMEA_DEBUG
+                Serial.print(c);
+                #endif
+                if (nmea.process(c) && strncmp(nmea.getSentence(), prefix, plen) == 0) return true;
+            } else {
+                yield();
+            }
+        }
+        return false;
+    }
+
     void loop() override {
 
         while (_gps_serial->available()) {