why is it base address?

[Altera_Forum]

I make leds light by using PIO of sopc! 

but i must change some code in niosII IDE!# include "system.h"# include "altera_avalon_pio_regs.h"# include "alt_types.h"   /*   * This is a freestanding application, so we want to use alt_main  * as the entry point. However, if the debugger is run on this  * application, it will try to set a breakpoint at main, which   * the application does not contain. The below line creates an  * alias so the debugger is able to set a breakpoint at main,   * yet the application retains alt_main as it&#39;s entry point.  */  int main (void) __attribute__ ((weak, alias ("alt_main")));   /*   * Use alt_main as entry point for this free-standing application  */  int alt_main (void) {  alt_u8 led = 0x2;  alt_u8 dir = 0;  volatile int i;    /*   * Infinitly shift a variable with one bit set back and forth, and write  * it to the LED PIO. Software loop provides delay element.  */  while (1)   {  if (led & 0x81)   {  dir = (dir ^ 0x1);  }   if (dir)   {  led = led >> 1;  }   else   {  led = led << 1;  }  IOWR_ALTERA_AVALON_PIO_DATA(PIO_0_BASE, led);  // Write led data to the address of pio_o_base  /*   * The delay element in this design has been written as a while loop  * to avoid confusing the software debugger. A tight, one line software  * delay loop such as:  * for(i=0; i<200000; i++);  * can cause problems when it is stepped through using a software debugger.  * The while loop below produces the same behavior as the for loop shown   * above, but without causing potential debugger problems.   */    i = 0;  while (i<20000)  i++;  }   return 0; }   I donot know why I must change LED_PIO_BASE to PIO_0_BASE?

[Altera_Forum]

It all depends on what name you gave to the PIO in SOPC Builder. 

This name will propagate to the system.h file that gets generated by the IDE.

[Altera_Forum]

If you have your system library compiled, look under the debug or release folder (whichever mode you compiled with) and look for system.h under system description folder. That system.h file has# defines for all the peripherals connected to that particular Nios II processor and that&#39;s where the name "PIO_0_BASE" is defined. So in your system your pio was called pio_0 or PIO_0. That software template assumes that the 8 bit pio in your system was called led_pio or LED_PIO which is why the compiler expected "LED_PIO_BASE" (that software template assumes you used a hardware reference design that was installed with Nios II).