File content as of revision 8:49f2b6a515ac:

#include "mbed.h"
#include "platform/mbed_thread.h"

using namespace std::chrono;

InterruptIn    user_button(USER_BUTTON);
DigitalOut     led(LED1);

bool           executeMainTask = false;
Timer          user_button_timer, loop_timer;
int            Ts_ms = 50;

void           button_fall();
void           button_rise();

AnalogIn       analogIn(PA_0);
float          dist = 0.0f;

int main()
{
    user_button.fall(&button_fall);
    user_button.rise(&button_rise);
    loop_timer.start();

    while (true) {

        loop_timer.reset();

        /* ------------- start hacking ------------- -------------*/

        if(executeMainTask) {

            dist = analogIn.read()*3.3f;
            
            printf("Measval: %d\r\n", (static_cast<int>(dist * 1000)));

            /* visual feedback that the main task is executed */
            led = !led;

        } else {
            led = 0;
        }

        /* ------------- stop hacking ------------- -------------*/

        int T_loop_ms = duration_cast<milliseconds>(loop_timer.elapsed_time()).count();
        int dT_loop_ms = Ts_ms - T_loop_ms;
        thread_sleep_for(dT_loop_ms);
    }
}

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

void button_rise()
{
    int t_button = duration_cast<milliseconds>(user_button_timer.elapsed_time()).count();
    user_button_timer.stop();
    if(t_button > 200) executeMainTask = !executeMainTask;
}