Nios II PIO Stimulus input signals for simulation with Modelsim/questasim

Hi guys,

It is my first post, so apologies if I leave out something important.

I have created a very simple Nios II environment with 2 buttons button as a PIO input width 2, and leds as a PIO output width 2.

I created the eclipse project, which will toggle the LED on and off. The led outputs simulate just fine in Modelsim. But the Buttons always just show X.

what I really want to do, is provide input stimulus signals like we would do for an HDL design. So I can have the LED toggle when the button signal goes high. I would flip the button on and off every 100 clock cycles and the LED would toggle with it. This is what I want to simulate, but in Nios instead of VHDL or verilog. In a VHDL simulation this is pretty trivial to accomplish.

I have been working on this all day and I cannot figure out how to do it.

I did try to just printf the value of the button, but it prints 0:

btn_in = IORD_ALTERA_AVALON_PIO_DATA(BUTTON_BASE);
printf("Button First Read: %d \n", btn_in);

It always reads 0 even though I set the PIO hardwire to 0x3 when I created it in Platform Designer.

What is the trick to this??

Code:

#include <stdio.h>
#include "altera_avalon_pio_regs.h"
#include "system.h"

int main()
{
int led_pattern = 0x01;
int btn_in;

btn_in = IORD_ALTERA_AVALON_PIO_DATA(BUTTON_BASE);
printf("Button First Read: %d \n", btn_in);
printf("Blinking LEDs \n");
while (1)
{
led_pattern = ~led_pattern; //invert led_pattern
IOWR_ALTERA_AVALON_PIO_DATA(LED_BASE,led_pattern); //macro which writes led_pattern to the LED_BASE memory address

}
return 0;

}

Nios:

what I want is something like this:

while(1) {

btn_in = IORD_ALTERA_AVALON_PIO_DATA(BUTTON_BASE);

IOWR_ALTERA_AVALON_PIO_DATA(LED_BASE, btn_in );

}

for that to work I need to be able to stimulate the buttons so the data read gives a value. I feel like this should be simple, but I am missing something.

Any ideas on that??

Thank you to anyone who takes the time to respond. Have a nice day.