CyclicTimer

A minimalistic cyclic timer class for Arduino, to run repeating tasks from loop()

Introduction

Sometimes you need a simple way to time multiple tasks, without wanting to have a complete scheduler (or not having the space for it, as on an Arduino Nano). This could be for example a measuring task plus a user interface task, as I had in my CO2 sensor.

Based on the Arduino main program loop() concept, CyclicTimer is a simple helper to create milli-second resolution timers, which you can decrement and check for zero, in which case they will auto-reload for the next interval. Kind of cooperative multi-tasking.

Don't expect millisecond accuracy, as we have no control over how long other tasks run (it is all 'scheduled' in the main loop, not in an interrupt routine). However, when reloading it takes into account any time already lapsed due to possible other tasks, so will catch up to run on average on the specified interval.

Note: maximum time is 65K miliseconds, so let's say one minute. Useful for sub-second or few-second intervals.

Methods

// cyclicTimer initialiser: creates new timer, but does not yet start it.
cyclicTimer::cyclicTimer()

// Set the period in milliseconds, and (re)start the timer.
void cyclicTimer::setPeriod(uint16_t newPeriodMilliseconds) 

// Restart timer with earlier specified period.
void cyclicTimer::reset(void)

// Decrement and test, and reload timer with compensation for elapsed time.
// Might be true for multiple times sequentially, if much time has elapsed.
bool cyclicTimer::tickAndTest(void) 

Example 1: CyclicBlink

See example file Blink.ino; based on the standard Arduino blink example. Within the main program loop, flash a LED every second (one second on, one second off). The basic statements looks like:

#include <CyclicTimer.h>
cyclicTimer oneSecondTicker;  // Instantiate a new timer

// In init(): tick for half second period
    oneSecondTicker.setPeriod(1000);

// In loop(): check (decrement with auto-reload)
    while(oneSecondTicker.tickAndTest()) { toggle_led(); }
    do_other_tasks();

You might expect an if before the test, but a while is useful if in the mean time already multiple periods have passed, so the timer can 'catch up'. I will do a second example with this (see the examples directory).

Example 2: CyclicBlinkPrint

Two timer tasks implemented with CyclicTimer, one running at 10 Hz incrementing a counter, the 2nd one running at 1 Hz printing the counter value.

Also, in the main program, a variable delay represeting some random main task neeing a random amount of time (0..500 ms), after which it will return to the main loop, giving time to the timer tasks.

As you can see, the 10 Hz task is still executed 10 times a second on average, although of course with significant jitter in the timing, as the main task only returneds and gives time for other tasks like tenthSecondTimer after up to 500 ms. However, no missed executions!

Normally, you would make sure to break up your main task such that it will not take that long before returning to loop() ...

Authors

• Kees Moerman - Initial work - My pages

License

Still to select, but permissive: feel free to use, no strings attached. Would be nice to acknowledge me.