Add Teensy 3.x chip select pin functions and transfer16() for AVR

SPI.cpp

 	updateCTAR(ctar);
 }
 
+bool SPIClass::pinIsChipSelect(uint8_t pin)
+{
+	if (pin == 10 || pin == 9 || pin == 6 || pin == 2 || pin == 15) return true;
+	if (pin >= 20 && pin <= 23) return true;
+	return false;
+}
+
+bool SPIClass::pinIsChipSelect(uint8_t pin1, uint8_t pin2)
+{
+	if (!pinIsChipSelect(pin1) || !pinIsChipSelect(pin2)) return false;
+	if ((pin1 ==  2 && pin2 == 10) || (pin1 == 10 && pin2 ==  2)) return false;
+	if ((pin1 ==  6 && pin2 ==  9) || (pin1 ==  9 && pin2 ==  6)) return false;
+	if ((pin1 == 20 && pin2 == 23) || (pin1 == 23 && pin2 == 20)) return false;
+	if ((pin1 == 21 && pin2 == 22) || (pin1 == 22 && pin2 == 21)) return false;
+	return true;
+}
+
+uint8_t SPIClass::setCS(uint8_t pin)
+{
+	switch (pin) {
+	  case 10: CORE_PIN10_CONFIG = PORT_PCR_MUX(2); return 0x01; // PTC4
+	  case 2:  CORE_PIN2_CONFIG  = PORT_PCR_MUX(2); return 0x01; // PTD0
+	  case 9:  CORE_PIN9_CONFIG  = PORT_PCR_MUX(2); return 0x02; // PTC3
+	  case 6:  CORE_PIN6_CONFIG  = PORT_PCR_MUX(2); return 0x02; // PTD4
+	  case 20: CORE_PIN20_CONFIG = PORT_PCR_MUX(2); return 0x04; // PTD5
+	  case 23: CORE_PIN23_CONFIG = PORT_PCR_MUX(2); return 0x04; // PTC2
+	  case 21: CORE_PIN21_CONFIG = PORT_PCR_MUX(2); return 0x08; // PTD6
+	  case 22: CORE_PIN22_CONFIG = PORT_PCR_MUX(2); return 0x08; // PTC1
+	  case 15: CORE_PIN15_CONFIG = PORT_PCR_MUX(2); return 0x10; // PTC0
+	}
+	return 0;
+}
+
 
 #endif
 

SPI.h

 		while (!(SPSR & _BV(SPIF))) ; // wait
 		return SPDR;
 	}
+	inline static uint16_t transfer16(uint16_t data) {
+		union { uint16_t val; struct { uint8_t lsb; uint8_t msb; }; } in, out;
+		in.val = data;
+		if (!(SPCR & _BV(DORD))) {
+			SPDR = in.msb;
+			while (!(SPSR & _BV(SPIF))) ;
+			out.msb = SPDR;
+			SPDR = in.lsb;
+			while (!(SPSR & _BV(SPIF))) ;
+			out.lsb = SPDR;
+		} else {
+			SPDR = in.lsb;
+			while (!(SPSR & _BV(SPIF))) ;
+			out.lsb = SPDR;
+			SPDR = in.msb;
+			while (!(SPSR & _BV(SPIF))) ;
+			out.msb = SPDR;
+		}
+		return out.val;
+	}
 	inline static void transfer(void *buf, size_t count) {
 		if (count == 0) return;
 		uint8_t *p = (uint8_t *)buf;
 	// Write to the SPI bus (MOSI pin) and also receive (MISO pin)
 	inline static uint8_t transfer(uint8_t data) {
 		SPDR = data;
-		asm volatile("nop");
 		while (!(SPSR & _BV(SPIF))) ; // wait
 		return SPDR;
 	}
 	inline static void setSCK(uint8_t pin) __attribute__((always_inline)) {
 		SPCR.setSCK(pin);
 	}
+	// return true if "pin" has special chip select capability
+	static bool pinIsChipSelect(uint8_t pin);
+	// return true if both pin1 and pin2 have independent chip select capability
+	static bool pinIsChipSelect(uint8_t pin1, uint8_t pin2);
+	// configure a pin for chip select and return its SPI_MCR_PCSIS bitmask
+	static uint8_t setCS(uint8_t pin);
 
 private:
 	static uint8_t interruptMode; // 0=none, 1=mask, 2=global