alt_irq_register question

[Altera_Forum]

Hello, 

 I have a specific question about using global variables instead of passing context argument.  What's the advantage to pass variable through the context argument if we can directly access to the global variable?  I have an example:  //Global Variable volatile int edge_capture;    static void handle_button_interrupts(void* context, alt_u32 id) {  /* Cast context to edge_capture's type. It is important that this be   * declared volatile to avoid unwanted compiler optimization.  */  volatile int* edge_capture_ptr = (volatile int*) context;  /* Store the value in the Button's edge capture register in *context. */  *edge_capture_ptr = IORD_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE);  /* Reset the Button's edge capture register. */  IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0); }  /* Initialize the button_pio. */  static void init_button_pio() {  /* Recast the edge_capture pointer to match the alt_irq_register() function  * prototype. */  void* edge_capture_ptr = (void*) &edge_capture;  /* Enable all 4 button interrupts. */  IOWR_ALTERA_AVALON_PIO_IRQ_MASK(BUTTON_PIO_BASE, 0xf);  /* Reset the edge capture register. */  IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0x0);  /* Register the interrupt handler. */  alt_irq_register( BUTTON_PIO_IRQ, edge_capture_ptr, handle_button_interrupts );  }   Instead, we could only use the edge_capture variable   static void handle_button_interrupts(void* context, alt_u32 id) {  /* Store the value in the Button's edge capture register in *context. */  edge_capture = IORD_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE);  /* Reset the Button's edge capture register. */  IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0); }  /* Initialize the button_pio. */  static void init_button_pio() {  /* Enable all 4 button interrupts. */  IOWR_ALTERA_AVALON_PIO_IRQ_MASK(BUTTON_PIO_BASE, 0xf);  /* Reset the edge capture register. */  IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0x0);  /* Register the interrupt handler. */  alt_irq_register( BUTTON_PIO_IRQ, NULL, handle_button_interrupts );  }   Best regards  Christian