This changes allow to use the SFE_UBLOX_GPS to be used as data storage and disable the implicit update of data that happened previously even with autoPVT set to true

Changes:
- add implicitUpdate parameter to setAutoPVT to control when the actual processing of the data happens
- add assumeAutoPVT method for use-cases where the receiver can't be controlled (no UART Tx line from MCU to receiver)
- change getPVT to respect autoPVTImplicitUpdate==false
- remove "virtual" from getPVT as it is not required anymore after the above changes

Author: FelixJirka

src/SparkFun_Ublox_Arduino_Library.cpp

@@ -1174,9 +1174,29 @@ uint8_t SFE_UBLOX_GPS::getNavigationFrequency(uint16_t maxWait)
   return (measurementRate);
 }
 
+//In case no config access to the GPS is possible and PVT is send cyclically already
+//set config to suitable parameters
+boolean SFE_UBLOX_GPS::assumeAutoPVT(boolean enabled, boolean implicitUpdate)
+{
+  boolean changes = autoPVT != enabled || autoPVTImplicitUpdate != implicitUpdate;
+  if(changes)
+  {
+    autoPVT = enabled;
+    autoPVTImplicitUpdate = implicitUpdate;
+  }
+  return changes;
+}
+
 //Enable or disable automatic navigation message generation by the GPS. This changes the way getPVT
 //works.
 boolean SFE_UBLOX_GPS::setAutoPVT(boolean enable, uint16_t maxWait)
+{
+  return setAutoPVT(enable, true, maxWait);
+}
+
+//Enable or disable automatic navigation message generation by the GPS. This changes the way getPVT
+//works.
+boolean SFE_UBLOX_GPS::setAutoPVT(boolean enable, boolean implicitUpdate, uint16_t maxWait)
 {
   packetCfg.cls = UBX_CLASS_CFG;
   packetCfg.id = UBX_CFG_MSG;
@@ -1187,8 +1207,10 @@ boolean SFE_UBLOX_GPS::setAutoPVT(boolean enable, uint16_t maxWait)
   payloadCfg[2] = enable ? 1 : 0; // rate relative to navigation freq.
 
   bool ok = sendCommand(packetCfg, maxWait);
-  if (ok)
+  if (ok){
     autoPVT = enable;
+    autoPVTImplicitUpdate = implicitUpdate;
+  }
   moduleQueried.all = false;
   return ok;
 }
@@ -1276,12 +1298,17 @@ uint8_t SFE_UBLOX_GPS::getSecond(uint16_t maxWait)
 //Get the latest Position/Velocity/Time solution and fill all global variables
 boolean SFE_UBLOX_GPS::getPVT(uint16_t maxWait)
 {
-  if (autoPVT)
+  if (autoPVT && autoPVTImplicitUpdate)
   {
     //The GPS is automatically reporting, we just check whether we got unread data
     checkUblox();
     return moduleQueried.all;
   }
+  else if(autoPVT && !autoPVTImplicitUpdate)
+  {
+    //Someone else has to call checkUblox for us...
+    return (false);
+  }
   else
   {
     //The GPS is not automatically reporting navigation position so we have to poll explicitly

src/SparkFun_Ublox_Arduino_Library.h

@@ -226,8 +226,10 @@ class SFE_UBLOX_GPS
 
 	boolean waitForResponse(uint8_t requestedClass, uint8_t requestedID, uint16_t maxTime = 250); //Poll the module until and ack is received
 
+	boolean assumeAutoPVT(boolean enabled, boolean implicitUpdate = true); //In case no config access to the GPS is possible and PVT is send cyclically already 
 	boolean setAutoPVT(boolean enabled, uint16_t maxWait = 250); //Enable/disable automatic PVT reports at the navigation frequency
-	virtual boolean getPVT(uint16_t maxWait = 1000);			 //Query module for latest group of datums and load global vars: lat, long, alt, speed, SIV, accuracies, etc. If autoPVT is disabled, performs an explicit poll and waits, if enabled does not block. Retruns true if new PVT is available.
+	boolean setAutoPVT(boolean enabled, boolean implicitUpdate, uint16_t maxWait = 250); //Enable/disable automatic PVT reports at the navigation frequency, with implicitUpdate == false accessing stale data will not issue parsing of data in the rxbuffer of your interface, instead you have to call checkUblox when you want to perform an update 
+	boolean getPVT(uint16_t maxWait = 1000);			 //Query module for latest group of datums and load global vars: lat, long, alt, speed, SIV, accuracies, etc. If autoPVT is disabled, performs an explicit poll and waits, if enabled does not block. Retruns true if new PVT is available.
 
 	int32_t getLatitude(uint16_t maxWait = 250);			//Returns the current latitude in degrees * 10^-7. Auto selects between HighPrecision and Regular depending on ability of module.
 	int32_t getLongitude(uint16_t maxWait = 250);			//Returns the current longitude in degrees * 10-7. Auto selects between HighPrecision and Regular depending on ability of module.
@@ -399,6 +401,7 @@ class SFE_UBLOX_GPS
 	const uint8_t I2C_POLLING_WAIT_MS = 25; //Limit checking of new characters to every X ms
 	unsigned long lastCheck = 0;
 	boolean autoPVT = false;	//Whether autoPVT is enabled or not
+	boolean autoPVTImplicitUpdate = true; // Whether autoPVT is triggered by accessing stale data (=true) or by a call to checkUblox (=false) 
 	boolean commandAck = false; //This goes true after we send a command and it's ack'd
 	uint8_t ubxFrameCounter;