Add spiPollingWait and setSPIpollingWait. Change delayMicroseconds(500) to delay(1)

examples/SPI/Example1_GetPosition/Example1_GetPosition.ino

@@ -86,6 +86,8 @@ void setup()
     while (1);
   }
   
+  //myGNSS.factoryDefault(); delay(5000); // Uncomment this line to reset the module back to its factory defaults
+
   myGNSS.setPortOutput(COM_PORT_SPI, COM_TYPE_UBX); //Set the SPI port to output UBX only (turn off NMEA noise)
   myGNSS.saveConfigSelective(VAL_CFG_SUBSEC_IOPORT); //Save (only) the communications port settings to flash and BBR
 }

examples/SPI/Example2_AutoPVT/Example2_AutoPVT.ino

@@ -79,12 +79,14 @@ void setup()
     while (1);
   }
   
+  //myGNSS.factoryDefault(); delay(5000); // Uncomment this line to reset the module back to its factory defaults
+
   myGNSS.setPortOutput(COM_PORT_SPI, COM_TYPE_UBX); //Set the SPI port to output UBX only (turn off NMEA noise)
   myGNSS.saveConfigSelective(VAL_CFG_SUBSEC_IOPORT); //Save (only) the communications port settings to flash and BBR
 
   myGNSS.setNavigationFrequency(2); //Produce two solutions per second
   myGNSS.setAutoPVT(true); //Tell the GNSS to "send" each solution
-  //myGNSS.saveConfiguration(); //Optional: Save the current settings to flash and BBR
+  //myGNSS.saveConfiguration(); //Optional: Save _all_ the current settings to flash and BBR
 }
 
 void loop()

keywords.txt

@@ -53,6 +53,7 @@ setPacketCfgPayloadSize	KEYWORD2
 begin	KEYWORD2
 end	KEYWORD2
 setI2CpollingWait	KEYWORD2
+setSPIpollingWait	KEYWORD2
 setI2CTransactionSize	KEYWORD2
 getI2CTransactionSize	KEYWORD2
 setSpiTransactionSize   KEYWORD2

src/SparkFun_u-blox_GNSS_Arduino_Library.cpp

@@ -514,6 +514,13 @@ void SFE_UBLOX_GNSS::setI2CpollingWait(uint8_t newPollingWait_ms)
   i2cPollingWait = newPollingWait_ms;
 }
 
+// Allow the user to change SPI polling wait
+// (the minimum interval between SPI data requests when no data is available - to avoid pounding the bus)
+void SFE_UBLOX_GNSS::setSPIpollingWait(uint8_t newPollingWait_ms)
+{
+  spiPollingWait = newPollingWait_ms;
+}
+
 //Sets the global size for I2C transactions
 //Most platforms use 32 bytes (the default) but this allows users to increase the transaction
 //size if the platform supports it
@@ -664,7 +671,7 @@ const char *SFE_UBLOX_GNSS::statusString(sfe_ublox_status_e stat)
   return "None";
 }
 
-// Check for the arrival of new I2C/Serial data
+// Check for the arrival of new I2C/Serial/SPI data
 
 //Allow the user to disable the "7F" check (e.g.) when logging RAWX data
 void SFE_UBLOX_GNSS::disableUBX7Fcheck(boolean disabled)
@@ -860,8 +867,20 @@ boolean SFE_UBLOX_GNSS::checkUbloxSpi(ubxPacket *incomingUBX, uint8_t requestedC
   _spiPort->beginTransaction(SPISettings(_spiSpeed, MSBFIRST, SPI_MODE0));
   digitalWrite(_csPin, LOW);
   uint8_t byteReturned = _spiPort->transfer(0xFF);
-  // Note to future self: I think the 0xFF check will cause problems when attempting to process (e.g.) RAWX data
-  // which could legitimately contain 0xFF within the data stream
+
+  // Note to future self: I think the 0xFF check might cause problems when attempting to process (e.g.) RAWX data
+  // which could legitimately contain 0xFF within the data stream. But the currentSentence check will certainly help!
+
+  // If we are not receiving a sentence (currentSentence == NONE) and the byteReturned is 0xFF,
+  // i.e. the module has no data for us, then delay for 
+  if ((byteReturned == 0xFF) && (currentSentence == NONE))
+  {
+    digitalWrite(_csPin, HIGH);
+    _spiPort->endTransaction();
+    delay(spiPollingWait);
+    return (true);
+  }
+
   while (byteReturned != 0xFF || currentSentence != NONE)
   {       
     process(byteReturned, incomingUBX, requestedClass, requestedID);
@@ -3208,7 +3227,7 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::waitForACKResponse(ubxPacket *outgoingUBX, ui
 
     } //checkUbloxInternal == true
 
-    delayMicroseconds(500);
+    delay(1); // Allow an RTOS to get an elbow in (#11)
   } //while (millis() - startTime < maxTime)
 
   // We have timed out...
@@ -3318,7 +3337,7 @@ sfe_ublox_status_e SFE_UBLOX_GNSS::waitForNoACKResponse(ubxPacket *outgoingUBX,
       }
     }
 
-    delayMicroseconds(500);
+    delay(1); // Allow an RTOS to get an elbow in (#11)
   }
 
   if (_printDebug == true)

src/SparkFun_u-blox_GNSS_Arduino_Library.h

@@ -577,6 +577,7 @@ public:
 	void end(void); //Stop all automatic message processing. Free all used RAM
 
 	void setI2CpollingWait(uint8_t newPollingWait_ms); // Allow the user to change the I2C polling wait if required
+	void setSPIpollingWait(uint8_t newPollingWait_ms); // Allow the user to change the SPI polling wait if required
 
 	//Set the max number of bytes set in a given I2C transaction
 	uint8_t i2cTransactionSize = 32; //Default to ATmega328 limit
@@ -1344,10 +1345,14 @@ private:
 	sfe_ublox_packet_buffer_e activePacketBuffer = SFE_UBLOX_PACKET_PACKETBUF;
 
 	//Limit checking of new data to every X ms
-	//If we are expecting an update every X Hz then we should check every half that amount of time
+	//If we are expecting an update every X Hz then we should check every quarter that amount of time
 	//Otherwise we may block ourselves from seeing new data
 	uint8_t i2cPollingWait = 100; //Default to 100ms. Adjusted when user calls setNavigationFrequency() or setHNRNavigationRate() or setMeasurementRate()
 
+	//The SPI polling wait is a little different. checkUbloxSpi will delay for this amount before returning if
+	//there is no data waiting to be read. This prevents waitForACKResponse from pounding the SPI bus too hard.
+	uint8_t spiPollingWait = 9; //Default to 9ms; waitForACKResponse delays for 1ms on top of this. User can adjust with setSPIPollingWait.
+
 	unsigned long lastCheck = 0;
 
 	uint16_t ubxFrameCounter; //Count all UBX frame bytes. [Fixed header(2bytes), CLS(1byte), ID(1byte), length(2bytes), payload(x bytes), checksums(2bytes)]