Fix in sam SPI library initialization when using multiple CS (extended API).

http://forum.arduino.cc/index.php?topic=189682.0

(Filtered from arduino/Arduino@b0dc317)

Author: cmaglie

arch/sam/SPI.cpp

@@ -11,15 +11,13 @@
 #include "SPI_Class.h"
 
 SPIClass::SPIClass(Spi *_spi, uint32_t _id, void(*_initCb)(void)) :
-	spi(_spi), id(_id), initCb(_initCb)
+	spi(_spi), id(_id), initCb(_initCb), initialized(false)
 {
 	// Empty
 }
 
 void SPIClass::begin() {
-	initCb();
-	SPI_Configure(spi, id, SPI_MR_MSTR | SPI_MR_PS | SPI_MR_MODFDIS);
-	SPI_Enable(spi);
+	init();
 
 	// NPCS control is left to the user
 
@@ -30,9 +28,7 @@ void SPIClass::begin() {
 }
 
 void SPIClass::begin(uint8_t _pin) {
-	initCb();
-	SPI_Configure(spi, id, SPI_MR_MSTR | SPI_MR_PS | SPI_MR_MODFDIS);
-	SPI_Enable(spi);
+	init();
 
 	uint32_t spiPin = BOARD_PIN_TO_SPI_PIN(_pin);
 	PIO_Configure(
@@ -47,6 +43,15 @@ void SPIClass::begin(uint8_t _pin) {
 	setBitOrder(_pin, MSBFIRST);
 }
 
+void SPIClass::init() {
+	if (initialized)
+		return;
+	initCb();
+	SPI_Configure(spi, id, SPI_MR_MSTR | SPI_MR_PS | SPI_MR_MODFDIS);
+	SPI_Enable(spi);
+	initialized = true;
+}
+
 void SPIClass::end(uint8_t _pin) {
 	uint32_t spiPin = BOARD_PIN_TO_SPI_PIN(_pin);
 	// Setting the pin as INPUT will disconnect it from SPI peripheral
@@ -55,6 +60,7 @@ void SPIClass::end(uint8_t _pin) {
 
 void SPIClass::end() {
 	SPI_Disable(spi);
+	initialized = false;
 }
 
 void SPIClass::setBitOrder(uint8_t _pin, BitOrder _bitOrder) {

arch/sam/SPI_Class.h

@@ -54,12 +54,15 @@ class SPIClass {
 	void setClockDivider(uint8_t _div) { setClockDivider(BOARD_SPI_DEFAULT_SS, _div); };
 
   private:
+	void init();
+
 	Spi *spi;
 	uint32_t id;
 	BitOrder bitOrder[SPI_CHANNELS_NUM];
 	uint32_t divider[SPI_CHANNELS_NUM];
 	uint32_t mode[SPI_CHANNELS_NUM];
 	void (*initCb)(void);
+	bool initialized;
 };
 
 #if SPI_INTERFACES_COUNT > 0