2.1.1 void _delay_ms
void _delay_ms(double __ms)
Perform a delay of __ms milliseconds, using _delay_loop_2().
The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz).
The maximal possible delay is 262.14 ms / F_CPU in MHz.
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 1/10 ms, providing delays up to 6.5535 seconds (independent from CPU frequency). The user will not be informed about decreased resolution.
If the avr-gcc toolchain has __builtin_avr_delay_cycles() support, maximal possible delay is 4294967.295 ms/ 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 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.
"__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.