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/* -*- mode: c++; c-basic-offset: 8; indent-tabs-mode: t -*- */
#include "utils.h"
void delayMicrosecondsInterruptible(unsigned int us)
{
#if F_CPU >= 16000000L
// for the 16 MHz clock on most Arduino boards
// for a one-microsecond delay, simply return. the overhead
// of the function call yields a delay of approximately 1 1/8 us.
if (--us == 0) return;
// the following loop takes a quarter of a microsecond (4 cycles)
// per iteration, so execute it four times for each microsecond of
// delay requested.
us <<= 2;
// account for the time taken in the preceeding commands.
us -= 2;
#else
// for the 8 MHz internal clock on the ATmega168
// for a one- or two-microsecond delay, simply return. the overhead of
// the function calls takes more than two microseconds. can't just
// subtract two, since us is unsigned; we'd overflow.
if (--us == 0) return;
if (--us == 0) return;
// the following loop takes half of a microsecond (4 cycles)
// per iteration, so execute it twice for each microsecond of
// delay requested.
us <<= 1;
// partially compensate for the time taken by the preceeding commands.
// we can't subtract any more than this or we'd overflow w/ small delays.
us--;
#endif
// busy wait
__asm__ __volatile__ (
"1: sbiw %0,1" "\n\t" // 2 cycles
"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
);
}
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