From 6e235622edb1b882401c77c171b0e738a093fd5b Mon Sep 17 00:00:00 2001
From: Martino Facchin <m.facchin@arduino.cc>
Date: Fri, 1 Dec 2017 15:41:18 +0100
Subject: [PATCH] Fix MCUs without MPCM0 register

---
 cores/arduino/HardwareSerial.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
index ecd791843..e99d503d8 100644
--- a/cores/arduino/HardwareSerial.cpp
+++ b/cores/arduino/HardwareSerial.cpp
@@ -100,7 +100,11 @@ void HardwareSerial::_tx_udr_empty_irq(void)
   // actually got written. Other r/w bits are preserved, and zeroes
   // written to the rest.
 
+#ifdef MPCM0
   *_ucsra = ((*_ucsra) & ((1 << U2X0) | (1 << MPCM0))) | (1 << TXC0);
+#else
+  *_ucsra = ((*_ucsra) & ((1 << U2X0) | (1 << TXC0)));
+#endif
 
   if (_tx_buffer_head == _tx_buffer_tail) {
     // Buffer empty, so disable interrupts
@@ -236,7 +240,11 @@ size_t HardwareSerial::write(uint8_t c)
     // be cleared when no bytes are left, causing flush() to hang
     ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
       *_udr = c;
+#ifdef MPCM0
       *_ucsra = ((*_ucsra) & ((1 << U2X0) | (1 << MPCM0))) | (1 << TXC0);
+#else
+      *_ucsra = ((*_ucsra) & ((1 << U2X0) | (1 << TXC0)));
+#endif
     }
     return 1;
   }