各位高手，我是菜菜鸟，最近开始玩NIOS，今天试了最简单的两个LED交替

闪烁实验，在建立NIOS工程后，调用HELLO—LED模块后，在BUILD PROJET 是

老出现如下的错误信息？到底是怎么回事，望高手指点。

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;

/*
* Infinitely 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(LED_PIO_BASE, led);------提示出错的地方。

Severity and Description Path Resource Location Creation Time Id
error: `LED_PIO_BASE' undeclared (first use in this function) hello_led_4 hello_led.c line 141 1241248626187 18