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+.. _arduino-volatile:
+
+volatile keyword
+================
+
+volatile is a keyword known as a variable *qualifier*, it is
+usually used before the datatype of a variable, to modify the way
+in which the compiler and subsequent program treats the variable.
+
+
+
+Declaring a variable volatile is a directive to the compiler. The
+compiler is software which translates your C/C++ code into the
+machine code, which are the real instructions for the Atmega chip
+in the Arduino.
+
+
+
+Specifically, it directs the compiler to load the variable from RAM
+and not from a storage register, which is a temporary memory
+location where program variables are stored and manipulated. Under
+certain conditions, the value for a variable stored in registers
+can be inaccurate.
+
+
+
+A variable should be declared volatile whenever its value can be
+changed by something beyond the control of the code section in
+which it appears, such as a concurrently executing thread. In the
+Arduino, the only place that this is likely to occur is in sections
+of code associated with interrupts, called an interrupt service
+routine.
+
+
+
+Example
+-------
+
+::
+
+    // toggles LED when interrupt pin changes state
+    
+    int pin = 13;
+    volatile int state = LOW;
+    
+    void setup()
+    {
+      pinMode(pin, OUTPUT);
+      attachInterrupt(0, blink, CHANGE);
+    }
+    
+    void loop()
+    {
+      digitalWrite(pin, state);
+    }
+    
+    void blink()
+    {
+      state = !state;
+    }
+
+
+
+See also
+--------
+
+
+-  `AttachInterrupt <http://arduino.cc/en/Reference/AttachInterrupt>`_
+
+