UART interrupt handler

Hi!

I've write small program with interrupt handler. I can't see the result ot ISR. May be somebody can explain my errors.

char uval=0;

ALTERA_AVALON_UART_INSTANCE( UART_0, uart_0 );

//----------------------------------------------------------------------------

void isr (void* context, alt_u32 id)

{

uval++;

IOWR_ALTERA_AVALON_PIO_DATA( PIO_1_BASE ,uval);

}

//----------------------------------------------------------------------------

int main()

{

char vv=1;

alt_sys_init();

alt_irq_register( UART_0_IRQ, &uart_0 , isr );

alt_irq_enabled();

while(1)

{

}

return 0;

}