File content as of revision 44:a65bc3e11481:

#include <mbed.h>

#include "PM2_Libary.h"
#include "Eigen/Dense.h"

# define M_PI 3.14159265358979323846  // number pi

// logical variable main task
bool do_execute_main_task = false;  // this variable will be toggled via the user button (blue button) to or not to execute the main task

// user button on nucleo board
Timer user_button_timer;            // create Timer object which we use to check if user button was pressed for a certain time (robust against signal bouncing)
InterruptIn user_button(PC_13);     // create InterruptIn interface object to evaluate user button falling and rising edge (no blocking code in ISR)
void user_button_pressed_fcn();     // custom functions which gets executed when user button gets pressed and released, definition below
void user_button_released_fcn();

int main()
{
    // while loop gets executed every main_task_period_ms milliseconds
    const int main_task_period_ms = 10;   // define main task period time in ms e.g. 50 ms -> main task runns 20 times per second
    Timer main_task_timer;                // create Timer object which we use to run the main task every main task period time in ms

    // a coutner
    uint32_t main_task_cntr = 0;

    // led on nucleo board
    DigitalOut user_led(LED1);      // create DigitalOut object to command user led

    // attach button fall and rise functions to user button object
    user_button.fall(&user_button_pressed_fcn);
    user_button.rise(&user_button_released_fcn);

    // start timer
    main_task_timer.start();

    while (true) { // this loop will run forever

        main_task_timer.reset();
        
       
        if (do_execute_main_task) {

        } else {
            
        }

        // user_led is switching its state every second
        if ( (main_task_cntr%(1000 / main_task_period_ms) == 0) && (main_task_cntr!=0) ) {
            user_led = !user_led;
        }
        main_task_cntr++;
        
        // do only output via serial what's really necessary (this makes your code slow)
        /*
        printf("IR sensor (mV): %3.3f, IR sensor (cm): %3.3f, SensorBar angle (rad): %3.3f, Speed M1 (rps) %3.3f, Position M2 (rot): %3.3f\r\n",
               ir_distance_mV,
               ir_distance_cm,
               sensor_bar_avgAngleRad,
               speedController_M1.getSpeedRPS(),
               positionController_M2.getRotation());
        */

        // read timer and make the main thread sleep for the remaining time span (non blocking)
        int main_task_elapsed_time_ms = std::chrono::duration_cast<std::chrono::milliseconds>(main_task_timer.elapsed_time()).count();
        thread_sleep_for(main_task_period_ms - main_task_elapsed_time_ms);
    }
}

void user_button_pressed_fcn()
{
    user_button_timer.start();
    user_button_timer.reset();
}

void user_button_released_fcn()
{
    // read timer and toggle do_execute_main_task if the button was pressed longer than the below specified time
    int user_button_elapsed_time_ms = std::chrono::duration_cast<std::chrono::milliseconds>(user_button_timer.elapsed_time()).count();
    user_button_timer.stop();
    if (user_button_elapsed_time_ms > 200) {
        do_execute_main_task = !do_execute_main_task;
    }
}