Multiple interrupts on single PIO input event

Hi,

I've been trying to use User push buttons in an applications. I've modified the Standard Ethernet Example from Altera to include VIC and shadow registers.

The design example configures the push buttons to generate an interrupt when pushed. The problem is that every push generates more than one interrupts even after I've cleared the interrupt in my ISR. Is there any documented way/Example of doing this? I've pasted my code below for reference.

Thanks!

Environment

------------

13.1 Quartus tools.

Standard Ethernet Example from Altera modified to add VIC and shadow registers.

Hello World Nios II application example.

Cyclone III (EP3C120F780C7) device.

Test Code

---------

volatile int count = 0;
static void handle_interrupt()
{
        // Clear all interrupts.
	IOWR_ALTERA_AVALON_PIO_EDGE_CAP(PERIPHERAL_SUBSYSTEM_BUTTON_PIO_BASE, 0xF);
	count++;
}
static void register_interrupt()
{
	// Enable all 4 button interrupts.
	IOWR_ALTERA_AVALON_PIO_IRQ_MASK(PERIPHERAL_SUBSYSTEM_BUTTON_PIO_BASE, 0xF);
	// Register handler.
	alt_ic_isr_register(PERIPHERAL_SUBSYSTEM_BUTTON_PIO_IRQ_INTERRUPT_CONTROLLER_ID,
						PERIPHERAL_SUBSYSTEM_BUTTON_PIO_IRQ,
						handle_interrupt, NULL, 0x0);
	alt_ic_irq_enable(PERIPHERAL_SUBSYSTEM_BUTTON_PIO_IRQ_INTERRUPT_CONTROLLER_ID,
					  PERIPHERAL_SUBSYSTEM_BUTTON_PIO_IRQ);
  }
int main()
{
	// Register PIO Interrupts.
	register_interrupt();
	printf("Hello from Nios II!\n");
	// Loop forever.
	while (1);
  return 0;
}