Make HardwareSerial.flush() compatible with Arduino 1.0 api

Author: edogaldo

STM32F1/cores/maple/HardwareSerial.cpp

@@ -193,7 +193,8 @@ size_t HardwareSerial::write(unsigned char ch) {
 	return 1;
 }
 
+/* edogaldo: Waits for the transmission of outgoing serial data to complete (Arduino 1.0 api specs) */
 void HardwareSerial::flush(void) {
-    usart_reset_rx(this->usart_device);
-    usart_reset_tx(this->usart_device);
+    while(!rb_is_empty(this->usart_device->wb)); // wait for TX buffer empty
+    while(!((this->usart_device->regs->SR) & (1<<USART_SR_TC_BIT))); // wait for TC (Transmission Complete) flag set 
 }

STM32F1/system/libmaple/include/libmaple/ring_buffer.h

@@ -52,9 +52,9 @@ extern "C"{
  * One byte is left free to distinguish empty from full. */
 typedef struct ring_buffer {
     volatile uint8 *buf; /**< Buffer items are stored into */
-    uint16 head;         /**< Index of the next item to remove */
-    uint16 tail;         /**< Index where the next item will get inserted */
-    uint16 size;         /**< Buffer capacity minus one */
+    volatile uint16 head;         /**< Index of the next item to remove */
+    volatile uint16 tail;         /**< Index where the next item will get inserted */
+    volatile uint16 size;         /**< Buffer capacity minus one */
 } ring_buffer;
 
 /**