錯誤 __builtin_avr_delay_cycles expects an integer constant.   

經過查詢發現是標頭檔案版本更新所致。delay.h檔案214行說明如下：

Note: The new implementation of _delay_us(double __us) with 
   __builtin_avr_delay_cycles(unsigned long) support is not backward compatible. 
  User can define __DELAY_BACKWARD_COMPATIBLE__ to get a backward compatible delay. 
  Also, the backward compatible 
  algorithm will be chosen if the code is compiled in a <em>freestanding 
  environment</em> (GCC option \c -ffreestanding), as the math functions 
  required for rounding are not available to the compiler then.

這樣解決方法就明顯了，新的定義和之前的不相容，

因此呼叫延時檔案#include <util/delay.h>之前加入#define __DELAY_BACKWARD_COMPATIBLE__ 即可。

例如：

#define F_CPU 8000000UL
#include <avr/io.h>
#define __DELAY_BACKWARD_COMPATIBLE__
#include <util/delay.h>

注：本文轉載自http://www.cnblogs.com/emouse/archive/2012/07/05/2577948.html