Atmel Studio 6中延时函数错误的解决方法

错误 __builtin_avr_delay_cycles expects an integer constant.   

经过查找发现是头文件版本更新所致。delay.h文件214行说明如下：

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.

这样解决方法就明显了，新的定义和之前的不兼容，

因此调用延时文件#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：本文转载自http://www.cnblogs.com/emouse/archive/2012/07/05/2577948.html