File content as of revision 2:3061fe655b7d:

#include "mbed.h"
#include "Adafruit_SSD1306.h"   // Adafruit_GFX library

Serial pc(SERIAL_TX, SERIAL_RX);
DigitalOut  myled(LED1);
DigitalOut  redLed(PA_12);
DigitalIn   myButton(PC_13);
DigitalIn   exButton(PC_11);
DigitalOut  myAnalogOut(PA_4);

BusOut my7Seg(PA_8, PA_9, PA_10, PC_9, PC_8, PC_7, PC_6, PA_11); // 8bit data
            // LSB,                                      , MSB
char    val7Seg[16] = {0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F,
                        0x77, 0x7C, 0x39, 0x5E, 0x79, 0x71};

char rxData[5];
bool flagRx = 0;

#define TEST1

#ifdef  TEST1

int main(void)
{
    while (1) {
        // change the voltage on the digital output pin by 0.1 * VCC
        //  and print what the measured voltage should be (assuming VCC = 3.3v)
        for (float n = 0.0f; n < 1.0f; n += 0.1f) {
            myAnalogOut = n;
//            myAnalogOut.write(n);

            pc.printf("output = %1.2f volts\n", myAnalogOut.read() * 3.3f);
            // turn on the led if the voltage is greater than 0.5f * VCC
            myled = (myAnalogOut > 0.5f) ? 1 : 0;
            wait(0.1);
        }
    }
}
#endif

#ifdef  TEST2
Ticker  DACtimer;
bool    flagTimer = 0;

void DACInt()
{
    flagTimer = 1;
}

main()
{
    // for 10kHz sine wave generation, it's needed to have 
    // a sampling frequency in 10 times of that frequency, 
    // or 100kHz -> 10us period
    DACtimer.attach_us(&DACInt, 10);
    float freq = 1000;      // 1kHz = 1000Hz
    while(1)
    {
        if (1 == flagTimer)
        {
            flagTime = 0;
            myAnalogOut = sin(n*3.14/180.0)*0.5+0.5;
            n++;
        }    
    }       
}
#endif