Arduino-Scheduler

This library implements an extended sub-set of the Arduino Scheduler class. Multiple loop() functions, tasks, may be started and run in a cooperative multi-tasking style. The tasks are run until they call yield() or delay(). The Arduino yield() function is replaced by an implementation in the library that allows context switching.

Tasks should be viewed as static and continuous. This implementation does not allocate tasks on the heap. They are allocated on the normal stack and linked into a cyclic run queue. One-shot tasks are not supported. Instead the task start function is extended with a setup function reference. Tasks are started with:

Scheduler.start(taskSetup, taskLoop [,taskStackSize]).

The tasks will start execution when the main task yields. The taskSetup is called first and once by the task followed by repeated calls to taskLoop. This works just as the Arduino setup() and loop() functions. There is also an optional parameter, taskStackSize. The default value depends on the architecture (128 bytes for AVR and 1024 bytes for SAM/SAMD/Teensy 3.X).

Scheduler.startLoop(taskLoop [,taskStackSize]).

A short hand version of start() is available when the taskSetup is NULL.

The Scheduler is a single-ton and the library creates the single instance.

This library also includes support for task synchronization and communication; Semaphores, Queues and Channels. There is also built-in support for checking the amount of stack head room, i.e. untouched stack space.

int bytes = Scheduler.stack();

The Scheduler member function stack() will scan the running task stack and determine the minimum amount of remaining stack during the execution so far. The example sketch SchedulerBlinkMax shows how this can be used.

Install

Download and unzip the Arduino-Scheduler library into your sketchbook libraries directory. Rename from Arduino-Scheduler-master to Arduino-Scheduler.

The Scheduler library and examples should be found in the Arduino IDE File>Examples menu.

Performance

There are several benchmark sketches in the examples directory. Below are some of the results.

Context Switch

Board	us	cycles
Arduino Mega 2560 (16 MHz)	12.64	203
Arduino Uno, Nano, Pro-Mini, etc (16 MHz)	11.00	176
Sparkfun SAMD21 (48 MHz)	2.60	125
Arduino Due (84 MHz)	1.36	115
Teensy 3.1 (72 MHz)	1.10	80
Teensy 3.6 (180 MHz)	0.43	78

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