[gnoduino: 44/237] Fixing 300 baud communication for serial.

[Lucian Langa <lucilanga src gnome org>]

commit 84c62a7d1e6ac4f430c6e7d72144aee166076cc1
Author: David A. Mellis <d mellis arduino cc>
Date:   Sat May 14 12:25:39 2011 -0400

    Fixing 300 baud communication for serial.
    
    Because UBBR is only 12 bits, we were overflowing it at 300 baud because of the use of the U2X bit.  Now we turn off U2X if it would yield a UBBR value that would overflow.
    
    Note that this breaks 300 baud communication with the computer on the Uno and Mega 2560 because the 8U2 USB-serial firmware has this same bug (and previously they cancelled each other out).  Since, however, it seems more likely that people will need to use 300 baud to communicate with other (legacy) hardware than with the computer, I'm making this change.  Issue for 8U2 firmware bug: http://code.google.com/p/arduino/issues/detail?id=542
    
    http://code.google.com/p/arduino/issues/detail?id=522

 arduino/cores/arduino/HardwareSerial.cpp |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)
---
diff --git a/arduino/cores/arduino/HardwareSerial.cpp b/arduino/cores/arduino/HardwareSerial.cpp
index d6d7b60..db6b149 100644
--- a/arduino/cores/arduino/HardwareSerial.cpp
+++ b/arduino/cores/arduino/HardwareSerial.cpp
@@ -278,6 +278,8 @@ void HardwareSerial::begin(unsigned long baud)
     use_u2x = false;
   }
 #endif
+
+try_again:
   
   if (use_u2x) {
     *_ucsra = 1 << _u2x;
@@ -286,6 +288,12 @@ void HardwareSerial::begin(unsigned long baud)
     *_ucsra = 0;
     baud_setting = (F_CPU / 8 / baud - 1) / 2;
   }
+  
+  if ((baud_setting > 4095) && use_u2x)
+  {
+    use_u2x = false;
+    goto try_again;
+  }
 
   // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
   *_ubrrh = baud_setting >> 8;