Enable interrupt mode of UART tx

Previous version of write will never use the interrupt mode
transmission, because it fails to check if holding register is
empty. This commit fix that, and several bugs related to
interrupt mode serial transmission.
When possible, it uses the tx FIFO, in order to reduce
the number of interrupts called and the overhead.

Author: descampsa

cores/arduino/UARTClass.cpp

@@ -168,7 +168,7 @@ int UARTClass::read( void )
 
 void UARTClass::flush( void )
 {
-  while (_tx_buffer->_iHead != _tx_buffer->_iTail); //wait for transmit data to be sent
+  while (_tx_buffer->_iHead != *(volatile int*)&(_tx_buffer->_iTail)); //wait for transmit data to be sent
   // Wait for transmission to complete
   while(!uart_tx_complete(CONFIG_UART_CONSOLE_INDEX));
 }
@@ -179,12 +179,11 @@ size_t UARTClass::write( const uint8_t uc_data )
     return(0);
 
   // Is the hardware currently busy?
-  if (_tx_buffer->_iTail != _tx_buffer->_iHead)
+  if (_tx_buffer->_iTail != _tx_buffer->_iHead || !uart_tx_ready(CONFIG_UART_CONSOLE_INDEX))
   {
     // If busy we buffer
     int l = (_tx_buffer->_iHead + 1) % UART_BUFFER_SIZE;
-    while (_tx_buffer->_iTail == l)
-      ; // Spin locks if we're about to overwrite the buffer. This continues once the data is sent
+    while (*(volatile int*)&(_tx_buffer->_iTail) == l); // Spin locks if we're about to overwrite the buffer. This continues once the data is sent
 
     _tx_buffer->_aucBuffer[_tx_buffer->_iHead] = uc_data;
     _tx_buffer->_iHead = l;
@@ -201,21 +200,29 @@ size_t UARTClass::write( const uint8_t uc_data )
 
 void UARTClass::IrqHandler( void )
 {
-  uint8_t uc_data;
-  int ret;
-  ret = uart_poll_in(CONFIG_UART_CONSOLE_INDEX, &uc_data);
-  
-  while ( ret != -1 ) {
-    _rx_buffer->store_char(uc_data);
+  uart_irq_update(CONFIG_UART_CONSOLE_INDEX);
+  // if irq is Receiver Data Available
+  if(uart_irq_rx_ready(CONFIG_UART_CONSOLE_INDEX))
+  {
+    uint8_t uc_data;
+    int ret;
     ret = uart_poll_in(CONFIG_UART_CONSOLE_INDEX, &uc_data);
+    
+    while ( ret != -1 ) {
+      _rx_buffer->store_char(uc_data);
+      ret = uart_poll_in(CONFIG_UART_CONSOLE_INDEX, &uc_data);
+    }
   }
 
-  // Do we need to keep sending data?
-  if (!uart_irq_tx_ready(CONFIG_UART_CONSOLE_INDEX))
+  // if irq is Transmitter Holding Register
+  else if(uart_irq_tx_ready(CONFIG_UART_CONSOLE_INDEX))
   {
-    if (_tx_buffer->_iTail != _tx_buffer->_iHead) {
-      uart_poll_out(CONFIG_UART_CONSOLE_INDEX, _tx_buffer->_aucBuffer[_tx_buffer->_iTail]);
-      _tx_buffer->_iTail = (unsigned int)(_tx_buffer->_iTail + 1) % UART_BUFFER_SIZE;
+    if(_tx_buffer->_iTail != _tx_buffer->_iHead)
+    {
+      int end = (_tx_buffer->_iTail < _tx_buffer->_iHead) ? _tx_buffer->_iHead:UART_BUFFER_SIZE;
+      int l = min(end - _tx_buffer->_iTail, UART_FIFO_SIZE);
+      uart_fifo_fill(CONFIG_UART_CONSOLE_INDEX, _tx_buffer->_aucBuffer+_tx_buffer->_iTail, l);
+      _tx_buffer->_iTail = (_tx_buffer->_iTail+l)%UART_BUFFER_SIZE;
     }
     else
     {

system/libarc32_arduino101/drivers/ns16550.c

@@ -340,7 +340,7 @@ unsigned char uart_poll_out(
 	)
 {
 	/* wait for transmitter to ready to accept a character */
-	while ((INBYTE(LSR(which)) & LSR_TEMT) == 0)
+	while ((INBYTE(LSR(which)) & LSR_THRE) == 0)
 		;
 
 	OUTBYTE(THR(which), outChar);
@@ -352,6 +352,8 @@ unsigned char uart_poll_out(
 *
 * uart_fifo_fill - fill FIFO with data
 *
+* It is up to the caller to make sure that FIFO capcity is not exceeded
+*
 * RETURNS: number of bytes sent
 */
 
@@ -362,8 +364,8 @@ int uart_fifo_fill(int which, /* UART on which to send */
 {
 	int i;
 
-	for (i = 0; i < size && (INBYTE(LSR(which)) &
-			LSR_BOTH_EMPTY) != 0; i++) {
+	for (i = 0; i < size ; i++) 
+	{
 		OUTBYTE(THR(which), txData[i]);
 	}
 	return i;
@@ -640,6 +642,19 @@ uint8_t uart_tx_complete(int which)
 	return INBYTE(LSR(which)) & LSR_TEMT;
 }
 
+/*******************************************************************************
+*
+* uart_tx_complete - check if tx holding register is empty
+*
+* RETURNS: zero if register is non-empty, 
+*          non-zero if register is empty (ready to receive new data)
+*/
+
+uint8_t uart_tx_ready(int which)
+{
+	return INBYTE(LSR(which)) & LSR_THRE;
+}
+
 /*******************************************************************************
 *
 * uart_loop_enable - enable loopback

system/libarc32_arduino101/drivers/uart.h

@@ -54,6 +54,9 @@ extern "C" {
 /* options for uart init */
 #define UART_OPTION_AFCE 0x01
 
+/* Size of the FIFO in bytes */
+#define UART_FIFO_SIZE 16
+
 /* generic UART info structure */
 struct uart_init_info {
 	int baud_rate;
@@ -92,6 +95,7 @@ int uart_break_check(int port);
 void uart_break_send(int port, int delay);
 void uart_disable(int port);
 uint8_t uart_tx_complete(int which);
+uint8_t uart_tx_ready(int which);
 void uart_loop_enable(int which);
 void uart_loop_disable(int which);