This library implements an extended sub-set of the Arduino Scheduler class. Multiple loop() functions, tasks, may be started and run in a collaborative 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 512 bytes for SAM/SAMD/Teensy 3.1).
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.
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.
There are several benchmark sketches in the examples directory. Below are some of the results.
| 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 |
| Board | Tasks | Stack (bytes) |
|---|---|---|
| Arduino Uno, Nano, Pro-Mini, etc (16 MHz) | 9 | 128 |
| Sparkfun SAMD21 (48 MHz) | 26 | 512 |
| Teensy 3.1 (72 MHz) | 26 | 512 |
| Arduino Mega 2560 (16 MHz) | 48 | 128 |
| Arduino Due (84 MHz) | 52 | 512 |
| Board | PROGMEM | SRAM (bytes) |
|---|---|---|
| Arduino Due (84 MHz) | 224 | NA |
| Arduino Uno, Nano, Pro-Mini, etc (16 MHz) | 546 | 42 |
| Arduino Mega 2560 (16 MHz) | 548 | 44 |
| Sparkfun SAMD21 (48 MHz) | NA | NA |
| Teensy 3.1 (72 MHz) | NA | NA |