3 files changed, 56 insertions, 16 deletions

diff --git a/cores/arduino/CDC.cpp b/cores/arduino/CDC.cpp
index 14a0eae..8605ce3 100644
--- a/cores/arduino/CDC.cpp
+++ b/cores/arduino/CDC.cpp
@@ -30,6 +30,25 @@ void Reboot()
 	asm volatile("jmp 0x7800");		// jump to bootloader - DiskLoader takes up last 2 kB
 }
 
+// Define constants and variables for buffering incoming serial data.  We're
+// using a ring buffer (I think), in which head is the index of the location
+// to which to write the next incoming character and tail is the index of the
+// location from which to read.
+#if (RAMEND < 1000)
+#define SERIAL_BUFFER_SIZE 16
+#else
+#define SERIAL_BUFFER_SIZE 64
+#endif
+
+struct ring_buffer
+{
+	unsigned char buffer[SERIAL_BUFFER_SIZE];
+	volatile int head;
+	volatile int tail;
+};
+
+ring_buffer cdc_rx_buffer = { { 0 }, 0, 0};
+
 typedef struct
 {
 	u32	dwDTERate;
@@ -111,33 +130,49 @@ void Serial_::end(void)
 {
 }
 
+void Serial_::accept(void) 
+{
+	ring_buffer *buffer = &cdc_rx_buffer;
+	int c = USB_Recv(CDC_RX); 
+	int i = (unsigned int)(buffer->head+1) % SERIAL_BUFFER_SIZE;
+	
+	// if we should be storing the received character into the location
+	// just before the tail (meaning that the head would advance to the
+	// current location of the tail), we're about to overflow the buffer
+	// and so we don't write the character or advance the head.
+	if (i != buffer->tail) {
+		buffer->buffer[buffer->head] = c;
+		buffer->head = i;
+	}
+}
+
 int Serial_::available(void)
 {
-	u8 avail = USB_Available(CDC_RX);
-	if (_serialPeek != -1)
-		avail++;
-	return avail;
+	ring_buffer *buffer = &cdc_rx_buffer;
+	return (unsigned int)(SERIAL_BUFFER_SIZE + buffer->head - buffer->tail) % SERIAL_BUFFER_SIZE;
 }
 
-//	peek is nasty
 int Serial_::peek(void)
 {
-	if (_serialPeek == -1)
-		_serialPeek = read();
-	return _serialPeek;
+	ring_buffer *buffer = &cdc_rx_buffer;
+	if (buffer->head == buffer->tail) {
+		return -1;
+	} else {
+		return buffer->buffer[buffer->tail];
+	}
 }
 
 int Serial_::read(void)
 {
-	int c;
-	if (_serialPeek != -1)
-	{
-		c = _serialPeek;
-		_serialPeek = -1;
+	ring_buffer *buffer = &cdc_rx_buffer;
+	// if the head isn't ahead of the tail, we don't have any characters
+	if (buffer->head == buffer->tail) {
+		return -1;
 	} else {
-		c = USB_Recv(CDC_RX);
-	}
-	return c;
+		unsigned char c = buffer->buffer[buffer->tail];
+		buffer->tail = (unsigned int)(buffer->tail + 1) % SERIAL_BUFFER_SIZE;
+		return c;
+	}	
 }
 
 void Serial_::flush(void)
diff --git a/cores/arduino/USBAPI.h b/cores/arduino/USBAPI.h
index 26a2032..1772c3c 100644
--- a/cores/arduino/USBAPI.h
+++ b/cores/arduino/USBAPI.h
@@ -27,11 +27,14 @@ extern USB_ USB;
 
 class Serial_ : public Stream
 {
+private:
+	ring_buffer *_cdc_rx_buffer;
 public:
 	void begin(uint16_t baud_count);
 	void end(void);
 
 	virtual int available(void);
+	virtual void accept(void);
 	virtual int peek(void);
 	virtual int read(void);
 	virtual void flush(void);
diff --git a/cores/arduino/USBCore.cpp b/cores/arduino/USBCore.cpp
index 398bc73..7924078 100644
--- a/cores/arduino/USBCore.cpp
+++ b/cores/arduino/USBCore.cpp
@@ -599,6 +599,8 @@ ISR(USB_GEN_vect)
 	{
 #ifdef CDC_ENABLED
 		USB_Flush(CDC_TX);				// Send a tx frame if found
+		while (USB_Available(CDC_RX))	// Handle received bytes (if any)
+			Serial.accept();
 #endif
 		
 		// check whether the one-shot period has elapsed.  if so, turn off the LED