Disable and re-enable USB interrupts while read breakValues from USB CDC

Author: sandeepmistry

cores/arduino/USB/CDC.cpp

@@ -298,10 +298,18 @@ Serial_::operator bool()
 }
 
 int32_t Serial_::readBreak() {
+	// disable the USB interrupt,
+	// to avoid clearing a breakValue that might occur 
+	// while processing the current break value
+	NVIC_DisableIRQ((IRQn_Type) USB_IRQn);
+
 	int32_t ret = breakValue;
 
 	breakValue = -1;
 
+	// re-enable the USB interupt
+	NVIC_EnableIRQ((IRQn_Type) USB_IRQn);
+
 	return ret;
 }