C undeclared(first use in this function) error

Question

I am writing a C program on NIOS II SBT for Eclplise to deal with Pushbuttons interrupts on a DE2 board, not that it matters but I keep running into this error 'keys_irq' undeclared(first use in this function) error. I dont know what I am doing wrong.

volatile int keys_edge_capture;
static void keys_int_init() {
    void* keys_edge_capture_ptr = (void*) &keys_edge_capture;
    // Enable all three keys as interrupt
    IOWR_ALTERA_AVALON_PIO_IRQ_MASK(PUSH_BUTTONS_BASE, 0x0F);
    // Reset edge capture register
    IOWR_ALTERA_AVALON_PIO_EDGE_CAP(PUSH_BUTTONS_BASE, 0x00);
    // Register ISR and place it on the interrupt table
    alt_ic_isr_register(PUSH_BUTTONS_IRQ_INTERRUPT_CONTROLLER_ID, PUSH_BUTTONS_IRQ,keys_irq, keys_edge_capture_ptr, 0x00);
}
void keys_irq(void* context) {
    // Recast context to keys_edge_capture type
    volatile int* keys_edge_capture_ptr = (volatile int*) context;
    // Read the edge capture to determine what triggered the interrupt
    *keys_edge_capture_ptr = IORD_ALTERA_AVALON_PIO_EDGE_CAP(PUSH_BUTTONS_BASE);

    if (*keys_edge_capture_ptr & 0b0100) // extract KEY2
        *(red_leds) = *(switches);
    else if (*keys_edge_capture_ptr & 0b1000) { // extract KEY3
       //do something
    }

    // clear the edge capture register
    IOWR_ALTERA_AVALON_PIO_EDGE_CAP(PUSH_BUTTONS_BASE, 0x00);

    // dummy instruction to synchronize the handler

    IORD_ALTERA_AVALON_PIO_EDGE_CAP(PUSH_BUTTONS_BASE);
    return;
}

int main()
{

    int SW_Value,Keys_Val;
    int mask = 0xF;


    while(1){
        SW_Value = *(switches) & mask;
        *(green_leds) = SW_Value;
         keys_int_init();
    }


  return 0;
}

Answer 1

The function keys_int_init is calling a reference to keys_irq. Since keys_irq is not yet defined, the compiler doesn't know what the function is. In order to avoid this, you can add something called a prototype at the beginning of the file, before keys_int_init is defined.

void keys_irq(void* context);

This tells the compiler what type the function is so it knows how to handle it.