GPIO-Usage-&-Used-Pins.md

@@ -58,6 +58,17 @@ somePin.mode(Mode::ALTERNATE);
 somePin.alternateFunction(5);
 ```
 
+> :warning: **WARNING: when configuring GPIOs you should disable interrupts to avoid concurrent calls to *mode()* (for example if it is done at runtime). This can be done since pins configuration is a very fast operation, but it should in general be avoided, in order not to compromise real-time capabilities of Miosix. A normal mutex would introduce more overhead.**
+> ```cpp
+> void someFunction()
+> {
+>    {
+>        FastInterruptDisableLock dLock; // disable interrupts
+>        somePin::mode(Mode::OUTPUT);
+>    } // dLock scope ends: re-enable interrupts
+> }
+> ```
+
 ### Discovery Board Pins
 These are some commonly used pins that you'll need when writing software for **Discovery boards**.