Hello-Skyward.md

+
+This is the third tutorial and here you will see how to establish serial communication between the microcontroller and your PC.  
+  
+More details are explained in the [Serial Communication](Serial-Communication) page.  
+
+## Introduction
+If you want to visualize the data you read from the sensor on your PC, you can use the *TRACE()* function: it is basically a *printf()* during the debugging, but it performs no action when the production code is released. You can use it as normal *printf()* (it has the same signature). In fact the *printf()* usage is almost prohibited by our [coding guidelines](Coding-Guidelines).  
+Everytime you call *TRACE()* in your code, the output data is redirected to the default serial port of the microcontroller. The default serial port for the STM32F407VG microcontroller is the `USART3` (default value set by Miosix), which corresponds to the GPIOs `PB10` (TX) and `PB11` (RX). The baud rate is by default set to `19200`.  
+  
+In order to read the *TRACE()* output you can use a serial to USB adapter and the connections you need are:
+- PB10 (TX) -> adapter RX
+- PB11 (RX) -> adapter TX
+- PB13 -> adapter CTS
+- PB14 -> adapter RST
+- GND -> adapter GND
+  
+Make sure you connect at least RX, TX and GND pins.  
+If you want to only receive data you can connect only the RX pin of the adapter (or TX if you only want to send data).  
+  
+Consider that you should set your serial adapter to work with 3.3 volts, since the microcontroller GPIOs work with this voltage level.  
+  
+You also need a program that is able to read those data from the USB port of your PC. You can use for example *GTKTerm* on Linux or *Putty* on Windows. You have to select the correct serial port (for example `/dev/ttyUSB0`) and set the correct baud rate.
+
+#### Note
+Consider that if you are using a different board, it may be possible that its USB connector is also connected to a microcontroller's serial port (i.e. you don't need to connect an external adapter). Just check which serial port is connected to the USB connector (e.g. `USARTX`).
+
+## Writing an entrypoint
+
+Here we will write an entrypoint that uses the *TRACE()* function in order to send data to the PC.
+
+#### hello-skyward.cpp
+```cpp
+#include <Common.h>
+
+using namespace miosix;
+
+int main()
+{
+    int i = 0;
+    while (true)
+    {
+        TRACE("%d : Hello Skyward! \n", i);
+        Thread::sleep(1000);
+        i++;
+    }
+
+    return 0;
+}
+```
+#### sbs.conf
+You should also add the entrypoint configuration to `sbs.conf`.  
+  
+First of all we need an `srcfiles` section in which we add the `Debug.cpp` file, on which the *TRACE()* function depends:
+```config
+[trace-include]
+Type:       srcfiles
+Files:      src/shared/Debug.cpp
+```
+
+Also, in order for the *TRACE()* function to act as a normal *printf()*, `DEBUG` has to be defined. We can define it in `sbs.conf` by inserting `-DDEBUG` in the defines section of our entrypoint configuration.  
+Notice that all the defines specified in `sbs.conf` start with `-D` followed by the string corresponding to the required define: if we want to define `MYDEF`, we will specify `-DMYDEF` in the SBS configuration file.  
+  
+Moreover the *trace_include* include is needed in order to compile also `Debug.cpp`, on which the *TRACE()* macro depends.
+
+```config
+[hello-skyward]
+Type:       test
+BoardId:    stm32f407vg_stm32f4discovery
+BinName:    hello-skyward
+Include:    %trace-include
+Defines:    -DDEBUG
+Main:       hello-skyward
+```
+
+## Run it!
+Same as before: build the entrypoint with `python sbs -b test-led-driver` and [flash the binary on the board](Flashing-on-a-Target-Board).
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