RTS/CTS support for Serial1 on Teensy LC & 3.x (experimental)

teensy3/HardwareSerial.h

 					  serial_format(format); }
 	virtual void end(void)		{ serial_end(); }
 	virtual void transmitterEnable(uint8_t pin) { serial_set_transmit_pin(pin); }
+	virtual bool attachRts(uint8_t pin) { return serial_set_rts(pin); }
+	virtual bool attachCts(uint8_t pin) { return serial_set_cts(pin); }
 	virtual int available(void)     { return serial_available(); }
 	virtual int peek(void)          { return serial_peek(); }
 	virtual int read(void)          { return serial_getchar(); }
 					  serial2_format(format); }
 	virtual void end(void)		{ serial2_end(); }
 	virtual void transmitterEnable(uint8_t pin) { serial2_set_transmit_pin(pin); }
+	virtual bool attachRts(uint8_t pin) { return serial2_set_rts(pin); }
+	virtual bool attachCts(uint8_t pin) { return serial2_set_cts(pin); }
 	virtual int available(void)     { return serial2_available(); }
 	virtual int peek(void)          { return serial2_peek(); }
 	virtual int read(void)          { return serial2_getchar(); }
 					  serial3_format(format); }
 	virtual void end(void)          { serial3_end(); }
 	virtual void transmitterEnable(uint8_t pin) { serial3_set_transmit_pin(pin); }
+	virtual bool attachRts(uint8_t pin) { return serial3_set_rts(pin); }
+	virtual bool attachCts(uint8_t pin) { return serial3_set_cts(pin); }
 	virtual int available(void)     { return serial3_available(); }
 	virtual int peek(void)          { return serial3_peek(); }
 	virtual int read(void)          { return serial3_getchar(); }

teensy3/serial1.c

 // Tunable parameters (relatively safe to edit these numbers)
 ////////////////////////////////////////////////////////////////
 
-#define TX_BUFFER_SIZE 64 // number of outgoing bytes to buffer
-#define RX_BUFFER_SIZE 64 // number of incoming bytes to buffer
+#define TX_BUFFER_SIZE     64 // number of outgoing bytes to buffer
+#define RX_BUFFER_SIZE     64 // number of incoming bytes to buffer
+#define RTS_HIGH_WATERMARK 40 // RTS requests sender to pause
+#define RTS_LOW_WATERMARK  26 // RTS allows sender to resume
 #define IRQ_PRIORITY  64  // 0 = highest priority, 255 = lowest
 
 
   static volatile uint8_t *transmit_pin=NULL;
   #define transmit_assert()   *transmit_pin = 1
   #define transmit_deassert() *transmit_pin = 0
+  static volatile uint8_t *rts_pin=NULL;
+  #define rts_assert()        *rts_pin = 0
+  #define rts_deassert()      *rts_pin = 1
 #elif defined(KINETISL)
   static volatile uint8_t *transmit_pin=NULL;
   static uint8_t transmit_mask=0;
   #define transmit_assert()   *(transmit_pin+4) = transmit_mask;
   #define transmit_deassert() *(transmit_pin+8) = transmit_mask;
+  static volatile uint8_t *rts_pin=NULL;
+  static uint8_t rts_mask=0;
+  #define rts_assert()        *(rts_pin+8) = rts_mask;
+  #define rts_deassert()      *(rts_pin+4) = rts_mask;
 #endif
 #if TX_BUFFER_SIZE > 255
 static volatile uint16_t tx_buffer_head = 0;
 	CORE_PIN1_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1);
 	rx_buffer_head = 0;
 	rx_buffer_tail = 0;
+	if (rts_pin) rts_deassert();
 }
 
 void serial_set_transmit_pin(uint8_t pin)
 int serial_set_rts(uint8_t pin)
 {
 	if (!(SIM_SCGC4 & SIM_SCGC4_UART0)) return 0;
+	if (pin < CORE_NUM_DIGITAL) {
+		rts_pin = portOutputRegister(pin);
+		#if defined(KINETISL)
+		rts_mask = digitalPinToBitMask(pin);
+		#endif
+		pinMode(pin, OUTPUT);
+		rts_assert();
+	} else {
+		rts_pin = NULL;
+		return 0;
+	}
+/*
 	if (pin == 6) {
 		CORE_PIN6_CONFIG = PORT_PCR_MUX(3);
 	} else if (pin == 19) {
 		return 0;
 	}
 	UART0_MODEM |= UART_MODEM_RXRTSE;
+*/
 	return 1;
 }
 
 {
 	if (!(SIM_SCGC4 & SIM_SCGC4_UART0)) return 0;
 	if (pin == 18) {
-		CORE_PIN18_CONFIG = PORT_PCR_MUX(3); // TODO: weak pullup or pulldown?
+		CORE_PIN18_CONFIG = PORT_PCR_MUX(3) | PORT_PCR_PE; // weak pulldown
 	} else if (pin == 20) {
-		CORE_PIN20_CONFIG = PORT_PCR_MUX(3); // TODO: weak pullup or pulldown?
+		CORE_PIN20_CONFIG = PORT_PCR_MUX(3) | PORT_PCR_PE; // weak pulldown
 	} else {
 		UART0_MODEM &= ~UART_MODEM_TXCTSE;
 		return 0;
 	if (++tail >= RX_BUFFER_SIZE) tail = 0;
 	c = rx_buffer[tail];
 	rx_buffer_tail = tail;
+	if (rts_pin) {
+		int avail;
+		if (head >= tail) avail = head - tail;
+		else avail = RX_BUFFER_SIZE + head - tail;
+		if (avail <= RTS_LOW_WATERMARK) rts_assert();
+	}
 	return c;
 }
 
 	UART0_C2 |= (UART_C2_RE | UART_C2_RIE | UART_C2_ILIE);
 #endif
 	rx_buffer_head = rx_buffer_tail;
+	if (rts_pin) rts_assert();
 }
 
 // status interrupt combines 
 				}
 			} while (--avail > 0);
 			rx_buffer_head = head;
+			if (rts_pin) {
+				int avail;
+				if (head >= tail) avail = head - tail;
+				else avail = RX_BUFFER_SIZE + head - tail;
+				if (avail >= RTS_HIGH_WATERMARK) rts_deassert();
+			}
 		}
 	}
 	c = UART0_C2;