void _delay

void _delay_ms(double __ms)

The maximal possible delay is 262.14ms / F_CPU in MHz with the highest resolution. When the user request delay which exceed the maximum possible one, _delay_ms() provides a decreased resolution functionality. In this mode _delay_ms() will work with a resolution of 1/10ms, providing delays up to 6.5535 seconds (independent from the CPU frequency). The user will not be informed about decreased resolution.

If the avr-gcc toolchain has __builtin_avr_delay_cycles() support, the maximal possible delay is 4294967.295ms/ F_CPU in MHz. For values greater than the maximal possible delay, overflows results in no delay i.e., 0ms.

Conversion of __ms into clock cycles may not always result in an integer. By default, the clock cycles rounded up to next integer. This ensures that the user gets at least __ms microseconds of delay.

Alternatively, by defining the macro __DELAY_ROUND_DOWN__, or __DELAY_ROUND_CLOSEST__, before including this header file, the algorithm can be made to round down, or round to closest integer, respectively.

Note:

The implementation of _delay_ms() based on __builtin_avr_delay_cycles() is not backward compatible with older implementations. In order to get functionality backward compatible with previous versions, the macro "__DELAY_BACKWARD_COMPATIBLE__" must be defined before including this header file. Also, the backward compatible algorithm will be chosen if the code is compiled in a freestanding environment (GCC option -ffreestanding), as the math functions required for rounding are not available to the compiler then.