File content as of revision 5:887081decd5c:

#include "mbed.h"
#include "platform/mbed_thread.h"
#include "iostream"
#include "string"
#include "BufferedSerial.h"
#include <math.h> 
#include <stdio.h> 

#define   pi 3.14159265358979323846 

using namespace std::chrono;

InterruptIn    user_button(USER_BUTTON);
DigitalOut     led(LED1);
BufferedSerial pc(USBTX, USBRX);

bool         executeMainTask = false;
Timer        user_button_timer, loop_timer;
int          Ts_ms = 1000;

void         button_fall(); // stuff
void         button_rise(); // stuff

void reverse(char* str, int len);
int intToStr(int x, char str[], int d);
void ftoa(float n, char* res, int afterpoint);

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

int main()
{
    // pc.baud(115200);
    user_button.fall(&button_fall);
    user_button.rise(&button_rise);
    loop_timer.reset();

    while (true) {

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

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

            Timer s;

            s.start();
            char res0[20]; 
            float val0 = 233.007;
            ftoa(val0, res0, 4);
            pc.write(res0, sizeof(res0));
            int buffered_time_ftoa = duration_cast<milliseconds>(s.elapsed_time()).count();
            thread_sleep_for(100);
            
            s.reset();
            char res1[20]; 
            float val1 = 233.007;
            ftoa(val1, res1, 4); 
            printf("%s\r\n", res1);
            int polled_time_ftoa = duration_cast<milliseconds>(s.elapsed_time()).count();
            thread_sleep_for(100);

            s.reset();
            char msg[] = "Hello World - buffered\n";
            pc.write(msg, sizeof(msg));
            int buffered_time = duration_cast<milliseconds>(s.elapsed_time()).count();
            thread_sleep_for(100);
            
            s.reset();
            printf("Hello World - blocking\n");
            int polled_time = duration_cast<milliseconds>(s.elapsed_time()).count();
            s.stop();
            thread_sleep_for(100);
            
            printf("printf buffered took %d us\n", buffered_time_ftoa);
            printf("printf blocking took %d us\n", polled_time_ftoa);
            printf("printf buffered took %d us\n", buffered_time);
            printf("printf blocking took %d us\n", polled_time);
            thread_sleep_for(100);


            
        } else {

        }

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

        if(executeMainTask) {
            led = !led;
        }
        int dT_loop = Ts_ms - duration_cast<milliseconds>(loop_timer.elapsed_time()).count();
        thread_sleep_for(dT_loop);
    }
}

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;
}

void reverse(char* str, int len) 
{ 
    int i = 0, j = len - 1, temp; 
    while (i < j) { 
        temp = str[i]; 
        str[i] = str[j]; 
        str[j] = temp; 
        i++; 
        j--; 
    } 
} 

int intToStr(int x, char str[], int d) 
{ 
    int i = 0; 
    while (x) { 
        str[i++] = (x % 10) + '0'; 
        x = x / 10; 
    } 
  
    // If number of digits required is more, then 
    // add 0s at the beginning 
    while (i < d) 
        str[i++] = '0'; 
  
    reverse(str, i); 
    str[i] = '\0'; 
    return i; 
} 

void ftoa(float n, char* res, int afterpoint) 
{ 
    // Extract integer part 
    int ipart = (int)n; 
  
    // Extract floating part 
    float fpart = n - (float)ipart; 
  
    // convert integer part to string 
    int i = intToStr(ipart, res, 0); 
  
    // check for display option after point 
    if (afterpoint != 0) { 
        res[i] = '.'; // add dot 
  
        // Get the value of fraction part upto given no. 
        // of points after dot. The third parameter  
        // is needed to handle cases like 233.007 
        fpart = fpart * pow(10, afterpoint); 
  
        intToStr((int)fpart, res + i + 1, afterpoint); 
    } 
}