problem of the example "key_intterput"

#include <stdio.h># include "system.h"# include "altera_avalon_pio_regs.h"# include "alt_types.h"# include "sys/alt_irq.h"# include "priv/alt_busy_sleep.h"

volatile alt_u32 done = 0;

static void KeyDown_interrupts(void* context, alt_u32 id)

{

IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0);

done++;

}

void InitPIO(void)

{

IOWR_ALTERA_AVALON_PIO_DIRECTION(LED_PIO_BASE, 0xFF);

IOWR_ALTERA_AVALON_PIO_DIRECTION(BUTTON_PIO_BASE, 0x00);

IOWR_ALTERA_AVALON_PIO_IRQ_MASK(BUTTON_PIO_BASE, 0xFF);

IOWR_ALTERA_AVALON_PIO_EDGE_CAP(BUTTON_PIO_BASE, 0x00);

alt_irq_register(BUTTON_PIO_IRQ, NULL, KeyDown_interrupts);

}

int main(void)

{

volatile alt_u32 key_state,old_state,new_state;

old_state = 0xff;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, old_state);

InitPIO();

while(1)

{

if(0 != done)

{

done--;

alt_busy_sleep(5000);

key_state = IORD_ALTERA_AVALON_PIO_DATA(BUTTON_PIO_BASE)&0xFF;

if(key_state == 0xff)

continue;

new_state = ~(old_state ^ key_state);

old_state = new_state;

IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, new_state);

}

}

return(0);

}