Rollover-safe elapsed time calculations for free-running counters. More...

#include <stdint.h>

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Functions
static uint32_t	timeElapsed (uint32_t now, uint32_t start)
	Compute the number of counter ticks elapsed from start to now.

static bool	hasIntervalElapsed (uint32_t now, uint32_t start, uint32_t interval)
	Check whether at least `interval` counter ticks have elapsed since `start`.

Detailed Description

Rollover-safe elapsed time calculations for free-running counters.

Timestamps taken from free-running counters such as micros(), millis() or runSecsX10 wrap back to zero when the counter overflows (micros() every ~71.6 minutes). Comparing absolute timestamps, E.g. micros() > startTime + interval, breaks when either the addition overflows or the counter wraps between the two samples. Unsigned modular subtraction is exact across a single wrap, so elapsed-time based comparisons remain correct provided the real elapsed time is less than one full counter period (I.e. the check runs at least once per counter period).

Both functions take now as a parameter rather than calling micros() internally so that callers can be unit tested with arbitrary counter values, including values either side of the wrap point.

Function Documentation

◆ hasIntervalElapsed()

static bool hasIntervalElapsed	(	uint32_t	now,
		uint32_t	start,
		uint32_t	interval
	)

inlinestatic

Check whether at least interval counter ticks have elapsed since start.

Rollover-safe replacement for now >= start + interval style comparisons. The boundary is inclusive: an elapsed time exactly equal to interval counts as elapsed.

Parameters

now	The current counter reading (E.g. micros())
start	The counter reading taken when the interval started
interval	The minimum number of ticks that must have elapsed

Returns: true if at least interval ticks have elapsed since start

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◆ timeElapsed()

static uint32_t timeElapsed	(	uint32_t	now,
		uint32_t	start
	)