add SPI support - tested with TitanX1.

Adafruit_GPS.cpp

@@ -455,8 +455,8 @@ size_t Adafruit_GPS::available(void) {
   if (gpsHwSerial) {
     return gpsHwSerial->available();
   }
-  if (gpsI2C) {
+  if (gpsI2C || gpsSPI) {
-    return 1; // I2C doesnt have 'availability' so always has a byte at least to read!
+    return 1; // I2C/SPI doesnt have 'availability' so always has a byte at least to read!
   }
   return 0;
 }
@@ -486,6 +486,19 @@ size_t Adafruit_GPS::write(uint8_t c) {
       return 1;
     }
   }
+  if (gpsSPI) {
+    gpsSPI->beginTransaction(gpsSPI_settings); 
+    if (gpsSPI_cs >= 0) {
+      digitalWrite(gpsSPI_cs, LOW);
+    }
+    c = gpsSPI->transfer(c);
+    if (gpsSPI_cs >= 0) {
+      digitalWrite(gpsSPI_cs, HIGH);
+    }
+    gpsSPI->endTransaction();
+    return 1;
+  }
+
   return 0;
 }
 
@@ -515,14 +528,14 @@ char Adafruit_GPS::read(void) {
     c = gpsHwSerial->read();
   }
   if (gpsI2C) {
-    if (_i2cbuff_idx <= _i2cbuff_max) {
+    if (_buff_idx <= _buff_max) {
-      c = _i2cbuffer[_i2cbuff_idx];
+      c = _i2cbuffer[_buff_idx];
-      _i2cbuff_idx++;
+      _buff_idx++;
     } else {
       // refill the buffer!
       if (Wire.requestFrom(0x10, GPS_MAX_I2C_TRANSFER, true) == GPS_MAX_I2C_TRANSFER) {
 	// got data!
-	_i2cbuff_max = 0;
+	_buff_max = 0;
 	char curr_char = 0;
 	for (int i=0; i<GPS_MAX_I2C_TRANSFER; i++) {
 	  curr_char = Wire.read();
@@ -531,19 +544,34 @@ char Adafruit_GPS::read(void) {
 	    continue;
 	  }
 	  last_char = curr_char;
-	  _i2cbuffer[_i2cbuff_max] = curr_char;
+	  _i2cbuffer[_buff_max] = curr_char;
-	  _i2cbuff_max++;
+	  _buff_max++;
 	}
-	_i2cbuff_max--;  // back up to the last valid slot
+	_buff_max--;  // back up to the last valid slot
-	if ((_i2cbuff_max == 0) && (_i2cbuffer[0] == 0x0A)) {
+	if ((_buff_max == 0) && (_i2cbuffer[0] == 0x0A)) {
-	  _i2cbuff_max = -1;  // ahh there was nothing to read after all
+	  _buff_max = -1;  // ahh there was nothing to read after all
 	}
-	_i2cbuff_idx = 0;
+	_buff_idx = 0;
       }
       return c;
     }
   }
 
+  if (gpsSPI) {
+    do {
+      gpsSPI->beginTransaction(gpsSPI_settings); 
+      if (gpsSPI_cs >= 0) {
+	digitalWrite(gpsSPI_cs, LOW);
+      }
+      c = gpsSPI->transfer(0xFF);
+      if (gpsSPI_cs >= 0) {
+	digitalWrite(gpsSPI_cs, HIGH);
+      }
+      gpsSPI->endTransaction();
+      // skip duplicate 0x0A's - but keep as part of a CRLF
+    } while (((c == 0x0A) && (last_char != 0x0D)) || (!isprint(c) && !isspace(c)) );
+    last_char = c;
+  }
   //Serial.print(c);
 
   currentline[lineidx++] = c;
@@ -612,6 +640,20 @@ Adafruit_GPS::Adafruit_GPS(TwoWire *theWire) {
   gpsI2C = theWire; // ...override gpsI2C
 }
 
+/**************************************************************************/
+/*!
+    @brief Constructor when using SPI
+    @param theSPI Pointer to an SPI device object
+    @param cspin The pin connected to the GPS CS, can be -1 if unused
+*/
+/**************************************************************************/
+Adafruit_GPS::Adafruit_GPS(SPIClass *theSPI, int8_t cspin) {
+  common_init();  // Set everything to common state, then...
+  gpsSPI = theSPI; // ...override gpsSPI
+  gpsSPI_cs = cspin;
+}
+
+
 /**************************************************************************/
 /*!
     @brief Initialization code used by all constructor types
@@ -623,6 +665,7 @@ void Adafruit_GPS::common_init(void) {
 #endif
   gpsHwSerial = NULL; // port pointer in corresponding constructor
   gpsI2C      = NULL;
+  gpsSPI      = NULL;
   recvdflag   = false;
   paused      = false;
   lineidx     = 0;
@@ -666,6 +709,15 @@ bool Adafruit_GPS::begin(uint32_t baud_or_i2caddr)
     gpsI2C->beginTransmission(_i2caddr);
     return (gpsI2C->endTransmission () == 0);
   }
+  if (gpsSPI) {
+    gpsSPI->begin();
+    gpsSPI_settings = SPISettings(baud_or_i2caddr, MSBFIRST, SPI_MODE0);
+    if (gpsSPI_cs >= 0) {
+      pinMode(gpsSPI_cs, OUTPUT);
+      digitalWrite(gpsSPI_cs, HIGH);
+    }
+  }
+
   delay(10);
   return true;
 }

Adafruit_GPS.h

@@ -35,7 +35,7 @@
   #include <SoftwareSerial.h>
 #endif
 #include <Wire.h>
-
+#include <SPI.h>
 
 /**************************************************************************/
 /**
@@ -112,6 +112,7 @@ class Adafruit_GPS : public Print{
 #endif
   Adafruit_GPS(HardwareSerial *ser); // Constructor when using HardwareSerial
   Adafruit_GPS(TwoWire *theWire); // Constructor when using I2C
+  Adafruit_GPS(SPIClass *theSPI, int8_t cspin); // Constructor when using SPI
 
   char *lastNMEA(void);
   boolean newNMEAreceived();
@@ -208,9 +209,13 @@ class Adafruit_GPS : public Print{
 #endif
   HardwareSerial *gpsHwSerial;
   TwoWire *gpsI2C;
+  SPIClass *gpsSPI;
+  int8_t gpsSPI_cs = -1;
+  SPISettings gpsSPI_settings = SPISettings(1000000, MSBFIRST, SPI_MODE0); // default
+  char _spibuffer[GPS_MAX_SPI_TRANSFER]; // for when we write data, we need to read it too!
   uint8_t _i2caddr;
   char _i2cbuffer[GPS_MAX_I2C_TRANSFER];
-  int8_t _i2cbuff_max = -1, _i2cbuff_idx = 0;
+  int8_t _buff_max = -1, _buff_idx = 0;
   char last_char = 0;
 };
 /**************************************************************************/

examples/GPS_SPI_EchoTest/GPS_SPI_EchoTest.ino

@@ -0,0 +1,41 @@
+// Test code for Adafruit GPS That Support Using SPI
+//
+// This code shows how to test a passthru between USB and SPI
+//
+// Pick one up today at the Adafruit electronics shop
+// and help support open source hardware & software! -ada
+
+#include <Adafruit_GPS.h>
+
+// Connect to the GPS on the hardware SPI port
+// with CS on pin #10
+Adafruit_GPS GPS(&SPI, 10);
+#define RESET_PIN 9
+
+void setup() {
+  // wait for hardware serial to appear
+  while (!Serial);
+
+  // make this baud rate fast enough to we aren't waiting on it
+  Serial.begin(115200);
+
+  Serial.println("Adafruit GPS library basic SPI test!");
+  pinMode(RESET_PIN, OUTPUT);
+  digitalWrite(RESET_PIN, LOW);
+  delay(10);
+  digitalWrite(RESET_PIN, HIGH);
+  delay(100);
+  GPS.begin(100000);  // use 100kHz for SPI data rate
+}
+
+
+void loop() {
+  if (Serial.available()) {
+    char c = Serial.read();
+    GPS.write(c);
+  }
+  if (GPS.available()) {
+    char c = GPS.read();
+    Serial.write(c);
+  }
+}