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The flush() method blocks until all characters in the serial buffer have been written to the uart _and_ transmitted. This is checked by waiting until the "TXC" (TX Complete) bit is set by the UART, signalling completion. This bit is cleared by write() when adding a new byte to the buffer and set by the hardware after tranmission ends, so it is always guaranteed to be zero from the moment the first byte in a sequence is queued until the moment the last byte is transmitted, and it is one from the moment the last byte in the buffer is transmitted until the first byte in the next sequence is queued. However, the TXC bit is also zero from initialization to the moment the first byte ever is queued (and then continues to be zero until the first sequence of bytes completes transmission). Unfortunately we cannot manually set the TXC bit during initialization, we can only clear it. To make sure that flush() would not (indefinitely) block when it is called _before_ anything was written to the serial device, the "transmitting" variable was introduced. This variable suggests that it is only true when something is transmitting, which isn't currently the case (it remains true after transmission is complete until flush() is called, for example). Furthermore, there is no need to keep the status of transmission, the only thing needed is to remember if anything has ever been written, so the corner case described above can be detected. This commit improves the code by: - Renaming the "transmitting" variable to _written (making it more clear and following the leading underscore naming convention). - Not resetting the value of _written at the end of flush(), there is no point to this. - Only checking the "_written" value once in flush(), since it can never be toggled off anyway. - Initializing the value of _written in both versions of _begin (though it probably gets initialized to 0 by default anyway, better to be explicit).
Arduino is an open-source physical computing platform based on a simple i/o board and a development environment that implements the Processing/Wiring language. Arduino can be used to develop stand-alone interactive objects or can be connected to software on your computer (e.g. Flash, Processing, MaxMSP). The boards can be assembled by hand or purchased preassembled; the open-source IDE can be downloaded for free. For more information, see the website at: http://www.arduino.cc/ or the forums at: http://arduino.cc/forum/ To report a *bug* in the software or to request *a simple enhancement* go to: http://github.com/arduino/Arduino/issues More complex requests and technical discussion should go on the Arduino Developers mailing list: https://groups.google.com/a/arduino.cc/forum/#!forum/developers If you're interested in modifying or extending the Arduino software, we strongly suggest discussing your ideas on the Developers mailing list *before* starting to work on them. That way you can coordinate with the Arduino Team and others, giving your work a higher chance of being integrated into the official release https://groups.google.com/a/arduino.cc/forum/#!forum/developers INSTALLATION Detailed instructions are in reference/Guide_Windows.html and reference/Guide_MacOSX.html. For Linux, see the Arduino playground: http://www.arduino.cc/playground/Learning/Linux CREDITS Arduino is an open source project, supported by many. The Arduino team is composed of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, Daniela Antonietti, and David A. Mellis. Arduino uses the GNU avr-gcc toolchain, avrdude, avr-libc, and code from Processing and Wiring. Icon and about image designed by ToDo: http://www.todo.to.it/