title: C: Prefix __ before function
body: <p>I have a question about why in some code is beeing used a prefix __ before function declaration? 
  For example:</p>
  
  <pre><code>__irq void Timer0IRQHandler(){
  
  T0IR=mMR0_INTERRUPT;    
  ptrTimer0InterruptFunction();    
  VICVectAddr=0x00;   
  </code></pre>
  
  <p>}</p>
  
  <p>and then:</p>
  
  <pre><code>VICVectAddr1  =(unsigned long)Timer0IRQHandler; 
  </code></pre>
  
  <p>It is a form of type projection? Or it is only used in embedded programming? How it exactly works? </p>