Add availableForWrite() on Teensy 2.0

teensy/HardwareSerial.cpp

 	return RX_BUFFER_SIZE + head - tail;
 }
 
+int HardwareSerial::availableForWrite(void)
+{
+	uint8_t head, tail;
+
+	head = rx_buffer_head;
+	tail = rx_buffer_tail;
+	if (head >= tail) return TX_BUFFER_SIZE - 1 - head + tail;
+	return tail - head - 1;
+}
+
 int HardwareSerial::peek(void)
 {
 	uint8_t head, tail;

teensy/HardwareSerial.h

 	virtual int peek(void);
 	virtual int read(void);
 	virtual void flush(void);
+	int availableForWrite(void);
 	void clear(void);
 #if ARDUINO >= 100
 	virtual size_t write(uint8_t);

usb_serial/usb_api.cpp

         return c;
 }
 
-#if ARDUINO >= 100
 size_t usb_serial_class::readBytes(char *buffer, size_t length)
 {
 	size_t count=0;
 	setReadError();
 	return count;
 }
-#endif
 
 
-#if ARDUINO >= 100
 void usb_serial_class::flush()
 {
 	send_now();
 }
-#else
+
+
 // discard any buffered input
-void usb_serial_class::flush()
+void usb_serial_class::clear()
 {
         uint8_t intr_state;
 
         }
 	peek_buf = -1;
 }
-#endif
+
 
 #if 0
 // transmit a character.
 #endif
 
 
+int usb_serial_class::availableForWrite()
+{
+	uint8_t intr_state, write_size;
+
+	if (!usb_configuration) return 0;
+	intr_state = SREG;
+	cli();
+	UENUM = CDC_TX_ENDPOINT;
+	write_size = CDC_TX_SIZE - UEBCLX;
+	SREG = intr_state;
+	return write_size;
+}
+
 // transmit a block of data
-#if ARDUINO >= 100
 size_t usb_serial_class::write(const uint8_t *buffer, uint16_t size)
-#else
-#define setWriteError()
-void usb_serial_class::write(const uint8_t *buffer, uint16_t size)
-#endif
 {
 	uint8_t timeout, intr_state, write_size;
-#if ARDUINO >= 100
 	size_t count=0;
-#endif
 
 	// if we're not online (enumerated and configured), error
 	if (!usb_configuration) {
 		write_size = CDC_TX_SIZE - UEBCLX;
 		if (write_size > size) write_size = size;
 		size -= write_size;
-#if ARDUINO >= 100
 		count += write_size;
-#endif
 
 #define ASM_COPY1(src, dest, tmp) "ld " tmp ", " src "\n\t" "st " dest ", " tmp "\n\t"
 #define ASM_COPY2(src, dest, tmp) ASM_COPY1(src, dest, tmp) ASM_COPY1(src, dest, tmp)
 	}
 	SREG = intr_state;
 end:
-#if ARDUINO >= 100
 	return count;
-#else
-	return;
-#endif
 }
 
 // transmit a string

usb_serial/usb_api.h

 	virtual void write(const uint8_t *buffer, uint16_t size);
 	virtual void write(const char *s)	{ write((const uint8_t *)s, strlen(s)); }
 #endif
+	int availableForWrite(void);
+	void clear(void);
 	void send_now(void);
 	uint32_t baud(void);
 	uint8_t stopbits(void);