HardwareSerial: don't call STM32 HAL for every bytes to transfer

Instead of calling HAL for each and every bytes,
try to call it only once for a string.
Several call may be needed to manage internal circular buffer
Fixes #1309

Signed-off-by: Alexandre Bourdiol <alexandre.bourdiol@st.com>

Author: ABOSTM

cores/arduino/HardwareSerial.cpp

@@ -327,7 +327,7 @@ int HardwareSerial::_tx_complete_irq(serial_t *obj)
 {
   // If interrupts are enabled, there must be more data in the output
   // buffer. Send the next byte
-  obj->tx_tail = (obj->tx_tail + 1) % SERIAL_TX_BUFFER_SIZE;
+  obj->tx_tail = (obj->tx_tail + obj->tx_size) % SERIAL_TX_BUFFER_SIZE;
 
   if (obj->tx_head == obj->tx_tail) {
     return -1;
@@ -467,8 +467,12 @@ void HardwareSerial::flush()
   // the hardware finished tranmission (TXC is set).
 }
 
-size_t HardwareSerial::write(uint8_t c)
+size_t HardwareSerial::write(const uint8_t *buffer, size_t size)
 {
+  tx_buffer_index_t i;
+  size_t size_tmp;
+  size_t ret = size;
+
   _written = true;
   if (isHalfDuplex()) {
     if (_rx_enabled) {
@@ -477,22 +481,59 @@ size_t HardwareSerial::write(uint8_t c)
     }
   }
 
-  tx_buffer_index_t i = (_serial.tx_head + 1) % SERIAL_TX_BUFFER_SIZE;
+  // If necessary split transfert till end of TX buffer
+  while (_serial.tx_head + size > SERIAL_TX_BUFFER_SIZE) {
+    size_t size_intermediate = SERIAL_TX_BUFFER_SIZE - _serial.tx_head;
 
-  // If the output buffer is full, there's nothing for it other than to
-  // wait for the interrupt handler to empty it a bit
-  while (i == _serial.tx_tail) {
-    // nop, the interrupt handler will free up space for us
+    write(buffer, size_intermediate);
+    size -= size_intermediate;
+    buffer += size_intermediate;
+  }
+
+  // Here size if less or equal to SERIAL_TX_BUFFER_SIZE, but SERIAL_TX_BUFFER_SIZE is not possible as tx_head = tx_tail is ambiguous empty or full
+  if (size == SERIAL_TX_BUFFER_SIZE) {
+    size_t size_intermediate = SERIAL_TX_BUFFER_SIZE - 1;
+
+    write(buffer, size_intermediate);
+    size -= size_intermediate;
+    buffer += size_intermediate;
+  }
+
+  size_tmp = size;
+
+  while (size_tmp) {
+    i = (_serial.tx_head + 1) % SERIAL_TX_BUFFER_SIZE;
+
+
+    // If the output buffer is full, there's nothing for it other than to
+    // wait for the interrupt handler to empty it a bit
+    while (i == _serial.tx_tail) {
+      // nop, the interrupt handler will free up space for us
+    }
+    _serial.tx_buff[_serial.tx_head] = *buffer;
+    _serial.tx_head = i;
+    size_tmp --;
+    buffer ++;
+  }
+
+  while ((_serial.tx_head != (_serial.tx_tail + size) % SERIAL_TX_BUFFER_SIZE)) {
+    // nop, previous transfert no yet completed
   }
 
-  _serial.tx_buff[_serial.tx_head] = c;
-  _serial.tx_head = i;
+  _serial.tx_size = size;
 
   if (!serial_tx_active(&_serial)) {
-    uart_attach_tx_callback(&_serial, _tx_complete_irq);
+    uart_attach_tx_callback(&_serial, _tx_complete_irq, size);
   }
 
-  return 1;
+  /* There is no real error management so just return transfer size requested*/
+  return ret;
+}
+
+size_t HardwareSerial::write(uint8_t c)
+{
+  uint8_t buff = c;
+  return write(&buff, 1);
 }
 
 void HardwareSerial::setRx(uint32_t _rx)

cores/arduino/HardwareSerial.h

@@ -143,7 +143,8 @@ class HardwareSerial : public Stream {
     {
       return write((uint8_t)n);
     }
-    using Print::write; // pull in write(str) and write(buf, size) from Print
+    size_t write(const uint8_t *buffer, size_t size);
+    using Print::write; // pull in write(str) from Print
     operator bool()
     {
       return true;

cores/arduino/stm32/uart.h

@@ -80,6 +80,7 @@ struct serial_s {
   uint16_t tx_head;
   volatile uint16_t rx_head;
   volatile uint16_t tx_tail;
+  size_t tx_size;
 };
 
 /* Exported constants --------------------------------------------------------*/
@@ -186,7 +187,7 @@ void uart_config_lowpower(serial_t *obj);
 size_t uart_write(serial_t *obj, uint8_t data, uint16_t size);
 int uart_getc(serial_t *obj, unsigned char *c);
 void uart_attach_rx_callback(serial_t *obj, void (*callback)(serial_t *));
-void uart_attach_tx_callback(serial_t *obj, int (*callback)(serial_t *));
+void uart_attach_tx_callback(serial_t *obj, int (*callback)(serial_t *), size_t size);
 
 uint8_t serial_tx_active(serial_t *obj);
 uint8_t serial_rx_active(serial_t *obj);

libraries/SrcWrapper/src/stm32/uart.c

@@ -723,7 +723,7 @@ void uart_attach_rx_callback(serial_t *obj, void (*callback)(serial_t *))
  * @param callback : function call at the end of transmission
  * @retval none
  */
-void uart_attach_tx_callback(serial_t *obj, int (*callback)(serial_t *))
+void uart_attach_tx_callback(serial_t *obj, int (*callback)(serial_t *), size_t size)
 {
   if (obj == NULL) {
     return;
@@ -734,7 +734,7 @@ void uart_attach_tx_callback(serial_t *obj, int (*callback)(serial_t *))
   HAL_NVIC_DisableIRQ(obj->irq);
 
   /* The following function will enable UART_IT_TXE and error interrupts */
-  HAL_UART_Transmit_IT(uart_handlers[obj->index], &obj->tx_buff[obj->tx_tail], 1);
+  HAL_UART_Transmit_IT(uart_handlers[obj->index], &obj->tx_buff[obj->tx_tail], size);
 
   /* Enable interrupt */
   HAL_NVIC_EnableIRQ(obj->irq);
@@ -810,11 +810,8 @@ void HAL_UART_RxCpltCallback(UART_HandleTypeDef *huart)
 void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart)
 {
   serial_t *obj = get_serial_obj(huart);
-
-  if (obj && obj->tx_callback(obj) != -1) {
-    if (HAL_UART_Transmit_IT(huart, &obj->tx_buff[obj->tx_tail], 1) != HAL_OK) {
-      return;
-    }
+  if (obj) {
+    obj->tx_callback(obj);
   }
 }