Easy nios II design

[Altera_Forum]

Hello, 

 I am a newbie with Quartus II and Nios II and I have been trying to do an easy nios design in order to light on a led when pressing a button. I am working on the Altera Cyclone III EP3C25F324 board. I think the problem comes from my code in nios II that I put below. I don't really know when to write "IOWR_ALTERA_AVALON_PIO_DATA(...);" maybe the problem comes from here. Plus, when I try to write some "printf", there is an error :  collect2: ld returned 1 exit status make: *** [button_led.elf] Error 1   Here is my program : # include "system.h"# include "altera_avalon_pio_regs.h"# include "alt_types.h"# include "stdio.h"# include "stdlib.h"  int alt_main (void) { alt_u8 led = 0x2; alt_u8 button = 0x2;  IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led); IOWR_ALTERA_AVALON_PIO_DATA(BUTTON_PIO_BASE, button);  while (1) { switch (button) {  case 0x1 : led=0x1; break;  case 0x2 : led=0x2; break;  case 0x4 : led=0x4; break;  case 0x8 : led=0x8; break; } }  Do someone can help me? Thank you very much,  Myriam

[Altera_Forum]

Hi Myriam, 

 Without getting into a discussion about better ways of handling buttons, here are some changes that should get your code doing what you expected it to do: # include "system.h"# include "altera_avalon_pio_regs.h"# include "alt_types.h"# include "stdio.h"# include "stdlib.h"  int alt_main (void) { alt_u8 led; alt_u8 button;  while (1) { button = IORD_ALTERA_AVALON_PIO_DATA(BUTTON_PIO_BASE);  switch (button) {  case 0x1 : led=0x1; break;  case 0x2 : led=0x2; break;  case 0x4 : led=0x4; break;  case 0x8 : led=0x8; break; } IOWR_ALTERA_AVALON_PIO_DATA(LED_PIO_BASE, led);  }   Note that the button PIO is read with an IORD_ function call.  I imagine your problem with printf is that you do not have a device configured for stdout.