Use UART TX FIFO

When possible, fill the tx FIFO in interrupt handler, in order to reduce
number of interrupts called and overhead.

Author: descampsa

cores/arduino/UARTClass.cpp

@@ -217,9 +217,12 @@ void UARTClass::IrqHandler( void )
   // 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:SERIAL_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

@@ -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;

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;