added availableForWrite

Author: delta-G

Diff for: cores/arduino/Serial.cpp

@@ -315,6 +315,12 @@ int UART::available() {
   return rxBuffer.available();
 }
 
+/* -------------------------------------------------------------------------- */
+int UART::availableForWrite() {
+/* -------------------------------------------------------------------------- */  
+  return txBuffer.availableForStore();
+}
+
 /* -------------------------------------------------------------------------- */
 int UART::peek() {
 /* -------------------------------------------------------------------------- */  

Diff for: cores/arduino/Serial.h

@@ -65,6 +65,7 @@ class UART : public arduino::HardwareSerial {
     size_t write(uint8_t* c, size_t len);
     size_t write_raw(uint8_t* c, size_t len);
     using Print::write; 
+    int availableForWrite();
     operator bool(); // { return true; }
 
   private: