alt_irq_register question

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