uCosm

Lightweight C++17 cooperative scheduler for microcontrollers.

• no heap allocation
• no task number limitation or pre-allocation
• platform independent
• scheduling tree
• customizable scheduling policy

flowchart LR

scheduler(Scheduler)

task1(Task)
task2(Task)
task3(Task)
schedTask(Scheduler)
schedTask
subTask1(Task)
subTask2(Task)

scheduler --> task1
scheduler --> task2
scheduler --> task3
scheduler --> schedTask

schedTask --> subTask1
schedTask --> subTask2

This library provides a basic skeleton implementation in the core directory, and two specialisations contained in the periodic and cfs (Completely Fair Scheduler) directories.

Examples

Periodic

#include <iostream>
#include "periodic/iperiodic_task.hpp"

struct Task final : ucosm::IPeriodicTask {
    void run() override {
        std::cout << "run " << this->getPeriod() << std::endl;
        if(mCounter++ == 10) {
            this->remove();
        }
    }
    int mCounter = 0;
};

#include <chrono>
#include "periodic/periodic_scheduler.hpp"

static ucosm::IPeriodicTask::tick_t getTick_ms() {
    return static_cast<ucosm::IPeriodicTask::tick_t>(
        std::chrono::duration_cast<std::chrono::milliseconds>(
            std::chrono::system_clock::now().time_since_epoch()
        ).count()
    );
}

int main() {

    ucosm::PeriodicScheduler sched(getTick_ms);

    Task t1;
    Task t2;

    t1.setPeriod(50);    // execute every 50 milliseconds
    t2.setPeriod(1000);  // execute every seconds

    sched.addTask(t1);
    sched.addTask(t2);

    while(!sched.empty()) {
        sched.run();
    }

    return 0;
}

CFS

#include <iostream>
#include "cfs/icfs_task.hpp"

struct Task final : ucosm::ICFSTask {
    void run() override {
        std::cout << "run " << (uint16_t)this->getPriority() << std::endl;
        if(mCounter++ == 10) {
            this->remove();
        }
    }
    int mCounter = 0;
};

#include <chrono>
#include "cfs/cfs_scheduler.hpp"

int main() {

    ucosm::CFSScheduler sched(getTick_us);

    Task t1;
    Task t2;

    t1.setPriority(2);
    t2.setPriority(4);

    sched.addTask(t1);
    sched.addTask(t2);

    while(!sched.empty()) {
        sched.run();
    }

    return 0;
}

Scheduler tree

In this library, the schedulers are also tasks. The task type can be passed as a template parameter to the scheduler.

Here we declare a periodic scheduler that schedules a CFS scheduler that schedules a periodic scheduler.

ucosm::PeriodicScheduler<ucosm::ICFSTask> periodicScheduler(getTick_ms);

ucosm::CFSScheduler<ucosm::IPeriodicTask> cfsScheduler(getTick_us);

ucosm::PeriodicScheduler periodicScheduler2(getTick_ms);

cfsScheduler.addTask(periodicScheduler);

periodicScheduler2.addTask(cfsScheduler);

Notes

The tasks storage is based on ulink and provides object lifetime safety which means that a task that is deleted will remove itself from its scheduler :

void foo() {
    Task tempTask;
    sched.addTask(tempTask);
}// tempTask removes itself from the scheduler at the end of the scope