int main(void) {
    HAL_Init();
    SystemInit();
    SystemClock_Config();
    cstm_f1_uart2_init(9600);
    initPC13();
    button_init();
    while(1) {
        if (cstm_uart2_data_available()) {
            cstm_uart2_receive_data(myBuff, GPS_CHUNK_SIZE, 10);
            decodeGPS(myBuff);
            if (latDir != ',') {    // Looks like we have lock and valid GPS data!
                curdist = distance(lat, lon);
                if (curdist > 100) zona = 6
                    else if (curdist <= 100) zona = 5
                        else if (curdist <= 50) zona = 4
                            else if (curdist <= 25) zona = 3
                                else if (curdist <= 15) zona = 2
                                    else if (curdist <= 5) zona = 1;
                HAL_GPIO_TogglePin(GPIOC, GPIO_PIN_13);
            } else {
                // Play mp3 - no signal file if button pressed
            }
            latDir = ',';       // Mark last data as not valid
        }
    }
}