Serial-Communication.md

+### Usage
+
+Standard input and output (`printf()` and `scanf()`) are redirected to the [default USART](#settings).
+
+Other serial ports can be used as follows, but they have to be configured first.
+```cpp
+#include <fcntl.h>
+//...
+fd=open("/dev/auxtty",O_RDWR);      //open serial port named auxtty
+if(fd<0) printf("Cannot open /dev/auxtty");
+
+char buffer[11];         //Buffer is 10 chars + '\0'
+read(fd, 10, buffer);    //Read 10 chars
+write(fd, 10, buffer);   //Write 10 chars
+```
+Pay attention to the baudrate at which the used port is set!
+
+### Settings
+The default serial for a certain board is set in `miosix/config/arch/<your_arch>/<your_board>/board_settings.h`
+
+```cpp
+const unsigned int defaultSerial=1;
+const unsigned int defaultSerialSpeed=19200;    //baudrate
+const bool defaultSerialFlowctrl=false;         //use rts/cts
+
+#define SERIAL_1_DMA                            //use the DMA
+```
+For the f407vg board, there's also another serial port that can be opened:
+```cpp
+//#define AUX_SERIAL "auxtty"    UNCOMMENT THIS TO OPEN THE SERIAL
+const unsigned int auxSerialSpeed=9600;
+const bool auxSerialFlowctrl=false;
+```
+
+The default serial port is opened in the *IRQBspInit()* method 
+inside `miosix/arch/<your arch>/<your board>/interfaces-impl/bsp.cpp`
+
+```cpp
+    DefaultConsole::instance().IRQset(intrusive_ref_ptr<Device>(
+     new STM32Serial(defaultSerial,defaultSerialSpeed,
+      defaultSerialFlowctrl ? STM32Serial::RTSCTS : STM32Serial::NOFLOWCTRL)));
+```
+
+While the other serial ports are opened in the *bspInit2()* method of the same file.
+```cpp
+void bspInit2()
+{
+      #ifdef WITH_FILESYSTEM
+      #ifdef AUX_SERIAL
+      intrusive_ref_ptr<DevFs> devFs=basicFilesystemSetup(SDIODriver::instance());
+      devFs->addDevice(AUX_SERIAL,
+        intrusive_ref_ptr<Device>(new STM32Serial(2,auxSerialSpeed,
+        auxSerialFlowctrl ? STM32Serial::RTSCTS : STM32Serial::NOFLOWCTRL)));
+      #else //AUX_SERIAL
+      basicFilesystemSetup(SDIODriver::instance());
+      #endif //AUX_SERIAL
+      #endif //WITH_FILESYSTEM
+}
+```
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