Atmel Studio 6.1 delay函数错误的解决方法

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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://blog.csdn.net/u010173859/article/details/20285627

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