void _delay_us(
	double __us)

Perform a delay of __us microseconds, using _delay_loop_1().

The macro F_CPU is supposed to be defined to a constant defining the CPU clock frequency (in Hertz).

The maximal possible delay is 768 us / F_CPU in MHz.

If the user requests a delay greater than the maximal possible one, _delay_us() will automatically call _delay_ms() instead. The user will not be informed about this case.

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

Conversion of __us 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 atleast __us microseconds of delay.

Alternatively, user can define __DELAY_ROUND_DOWN__ and __DELAY_ROUND_CLOSEST__ to round down and round to closest integer.

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 freestanding environment (GCC option -ffreestanding), as the math functions required for rounding are not available to the compiler then.