[SoftwareSerial] Add function to set interrupt priority

Fixes #751

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

Diff for: libraries/SoftwareSerial/src/SoftwareSerial.cpp

@@ -419,3 +419,8 @@ int SoftwareSerial::peek()
   // Read from "head"
   return _receive_buffer[_receive_buffer_head];
 }
+
+void SoftwareSerial::setInterruptPriority(uint32_t preemptPriority, uint32_t subPriority)
+{
+  timer.setInterruptPriority(preemptPriority, subPriority);
+}

Diff for: libraries/SoftwareSerial/src/SoftwareSerial.h

@@ -118,6 +118,8 @@ class SoftwareSerial : public Stream {
       return true;
     }
 
+    static void setInterruptPriority(uint32_t preemptPriority, uint32_t subPriority);
+
     using Print::write;
 };