void _delay_loop_1(uint8_t __count)
Delay loop using an 8-bit counter __count, so up to 256 iterations are possible. (The value 256 would have to be passed as 0.) The loop executes three CPU cycles per iteration, not including the overhead the compiler needs to setup the counter register.
Thus, at a CPU speed of 1 MHz, delays of up to 768 microseconds can be achieved.