[U(S)ART] hardware flow control support (#1634)

* Add RTS/CTS configuration interface

void setRts(_rts);
void setCts(_cts);
void setRtsCts(_rts, _cts);
Add constructor with RTS/CTS parameters

These APIs accept either uint32_t pin number or PinName.

Author: akasona

Diff for: cores/arduino/HardwareSerial.cpp

@@ -115,14 +115,14 @@
 #endif // HAVE_HWSERIALx
 
 // Constructors ////////////////////////////////////////////////////////////////
-HardwareSerial::HardwareSerial(uint32_t _rx, uint32_t _tx)
+HardwareSerial::HardwareSerial(uint32_t _rx, uint32_t _tx, uint32_t _rts, uint32_t _cts)
 {
-  init(digitalPinToPinName(_rx), digitalPinToPinName(_tx));
+  init(digitalPinToPinName(_rx), digitalPinToPinName(_tx), digitalPinToPinName(_rts), digitalPinToPinName(_cts));
 }
 
-HardwareSerial::HardwareSerial(PinName _rx, PinName _tx)
+HardwareSerial::HardwareSerial(PinName _rx, PinName _tx, PinName _rts, PinName _cts)
 {
-  init(_rx, _tx);
+  init(_rx, _tx, _rts, _cts);
 }
 
 HardwareSerial::HardwareSerial(void *peripheral, HalfDuplexMode_t halfDuplex)
@@ -286,14 +286,16 @@ HardwareSerial::HardwareSerial(PinName _rxtx)
   init(NC, _rxtx);
 }
 
-void HardwareSerial::init(PinName _rx, PinName _tx)
+void HardwareSerial::init(PinName _rx, PinName _tx, PinName _rts, PinName _cts)
 {
   if (_rx == _tx) {
     _serial.pin_rx = NC;
   } else {
     _serial.pin_rx = _rx;
   }
   _serial.pin_tx = _tx;
+  _serial.pin_rts = _rts;
+  _serial.pin_cts = _cts;
   _serial.rx_buff = _rx_buffer;
   _serial.rx_head = 0;
   _serial.rx_tail = 0;
@@ -575,6 +577,38 @@ void HardwareSerial::setTx(PinName _tx)
   _serial.pin_tx = _tx;
 }
 
+void HardwareSerial::setRts(uint32_t _rts)
+{
+  _serial.pin_rts = digitalPinToPinName(_rts);
+}
+
+void HardwareSerial::setCts(uint32_t _cts)
+{
+  _serial.pin_cts = digitalPinToPinName(_cts);
+}
+
+void HardwareSerial::setRtsCts(uint32_t _rts, uint32_t _cts)
+{
+  _serial.pin_rts = digitalPinToPinName(_rts);
+  _serial.pin_cts = digitalPinToPinName(_cts);
+}
+
+void HardwareSerial::setRts(PinName _rts)
+{
+  _serial.pin_rts = _rts;
+}
+
+void HardwareSerial::setCts(PinName _cts)
+{
+  _serial.pin_cts = _cts;
+}
+
+void HardwareSerial::setRtsCts(PinName _rts, PinName _cts)
+{
+  _serial.pin_rts = _rts;
+  _serial.pin_cts = _cts;
+}
+
 void HardwareSerial::setHalfDuplex(void)
 {
   _serial.pin_rx = NC;

Diff for: cores/arduino/HardwareSerial.h

@@ -110,8 +110,8 @@ class HardwareSerial : public Stream {
     serial_t _serial;
 
   public:
-    HardwareSerial(uint32_t _rx, uint32_t _tx);
-    HardwareSerial(PinName _rx, PinName _tx);
+    HardwareSerial(uint32_t _rx, uint32_t _tx, uint32_t _rts = NUM_DIGITAL_PINS, uint32_t _cts = NUM_DIGITAL_PINS);
+    HardwareSerial(PinName _rx, PinName _tx, PinName _rts = NC, PinName _cts = NC);
     HardwareSerial(void *peripheral, HalfDuplexMode_t halfDuplex = HALF_DUPLEX_DISABLED);
     HardwareSerial(uint32_t _rxtx);
     HardwareSerial(PinName _rxtx);
@@ -155,6 +155,14 @@ class HardwareSerial : public Stream {
     void setRx(PinName _rx);
     void setTx(PinName _tx);
 
+    // Enable HW flow control on RTS, CTS or both
+    void setRts(uint32_t _rts);
+    void setCts(uint32_t _cts);
+    void setRtsCts(uint32_t _rts, uint32_t _cts);
+    void setRts(PinName _rts);
+    void setCts(PinName _cts);
+    void setRtsCts(PinName _rts, PinName _cts);
+
     // Enable half-duplex mode by setting the Rx pin to NC
     // This needs to be done before the call to begin()
     void setHalfDuplex(void);
@@ -170,7 +178,7 @@ class HardwareSerial : public Stream {
     bool _rx_enabled;
     uint8_t _config;
     unsigned long _baud;
-    void init(PinName _rx, PinName _tx);
+    void init(PinName _rx, PinName _tx, PinName _rts = NC, PinName _cts = NC);
     void configForLowPower(void);
 };
 

Diff for: cores/arduino/stm32/uart.h

@@ -71,6 +71,8 @@ struct serial_s {
   int (*tx_callback)(serial_t *);
   PinName pin_tx;
   PinName pin_rx;
+  PinName pin_rts;
+  PinName pin_cts;
   IRQn_Type irq;
   uint8_t index;
   uint8_t recv;

Diff for: libraries/SrcWrapper/src/stm32/uart.c

@@ -110,6 +110,8 @@ void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
   /* Determine the U(S)ART peripheral to use (USART1, USART2, ...) */
   USART_TypeDef *uart_tx = pinmap_peripheral(obj->pin_tx, PinMap_UART_TX);
   USART_TypeDef *uart_rx = pinmap_peripheral(obj->pin_rx, PinMap_UART_RX);
+  USART_TypeDef *uart_rts = pinmap_peripheral(obj->pin_rts, PinMap_UART_RTS);
+  USART_TypeDef *uart_cts = pinmap_peripheral(obj->pin_cts, PinMap_UART_CTS);
 
   /* Pin Tx must not be NP */
   if (uart_tx == NP) {
@@ -121,15 +123,28 @@ void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
     core_debug("ERROR: [U(S)ART] Rx pin has no peripheral!\n");
     return;
   }
+  /* Pin RTS must not be NP if flow control is enabled */
+  if ((obj->pin_rts != NC) && (uart_rts == NP)) {
+    core_debug("ERROR: [U(S)ART] RTS pin has no peripheral!\n");
+    return;
+  }
+  /* Pin CTS must not be NP if flow control is enabled */
+  if ((obj->pin_cts != NC) && (uart_cts == NP)) {
+    core_debug("ERROR: [U(S)ART] CTS pin has no peripheral!\n");
+    return;
+  }
 
   /*
    * Get the peripheral name (USART1, USART2, ...) from the pin
    * and assign it to the object
    */
   obj->uart = pinmap_merge_peripheral(uart_tx, uart_rx);
+  /* We also merge RTS/CTS and assert all pins belong to the same instance */
+  obj->uart = pinmap_merge_peripheral(obj->uart, uart_rts);
+  obj->uart = pinmap_merge_peripheral(obj->uart, uart_cts);
 
   if (obj->uart == NP) {
-    core_debug("ERROR: [U(S)ART] Rx and Tx pins peripherals mismatch!\n");
+    core_debug("ERROR: [U(S)ART] Rx/Tx/RTS/CTS pins peripherals mismatch!\n");
     return;
   }
 
@@ -290,6 +305,17 @@ void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
     pinmap_pinout(obj->pin_rx, PinMap_UART_RX);
   }
 
+  /* Configure flow control */
+  uint32_t flow_control = UART_HWCONTROL_NONE;
+  if (uart_rts != NP) {
+    flow_control |= UART_HWCONTROL_RTS;
+    pinmap_pinout(obj->pin_rts, PinMap_UART_RTS);
+  }
+  if (uart_cts != NP) {
+    flow_control |= UART_HWCONTROL_CTS;
+    pinmap_pinout(obj->pin_cts, PinMap_UART_CTS);
+  }
+
   /* Configure uart */
   uart_handlers[obj->index] = huart;
   huart->Instance          = (USART_TypeDef *)(obj->uart);
@@ -298,7 +324,7 @@ void uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
   huart->Init.StopBits     = stopbits;
   huart->Init.Parity       = parity;
   huart->Init.Mode         = UART_MODE_TX_RX;
-  huart->Init.HwFlowCtl    = UART_HWCONTROL_NONE;
+  huart->Init.HwFlowCtl    = flow_control;
   huart->Init.OverSampling = UART_OVERSAMPLING_16;
 #if !defined(STM32F1xx) && !defined(STM32F2xx) && !defined(STM32F4xx)\
  && !defined(STM32L1xx)