See https://medium.com/@ly.lee/sneak-peek-of-pinetime-smart-watch-and-why-its-perfect-for-teaching-iot-81b74161c159

pinetime-main.rs

///  main() will be called at Mynewt startup. It replaces the C version of the main() function.
#[no_mangle]                 //  Don't mangle the name "main"
extern "C" fn main() -> ! {  //  Declare extern "C" because it will be called by Mynewt
    //  Initialise the Mynewt OS.
    mynewt::sysinit();

    //  TODO: Start the Server Transport for sending sensor data to the cloud.
    //  sensor_network::start_server_transport()
    //    .expect("NET fail");

    //  Start a sensor listener that polls a simulated tmperature sensor.
    //  Will be changed to handle touch events instead.
    app_sensor::start_sensor_listener()
        .expect("TMP fail");

    //  Start Bluetooth Beacon.  TODO: Create a safe wrapper for starting Bluetooth LE.
    extern { fn start_ble() -> i32; }
    let rc = unsafe { start_ble() };
    assert!(rc == 0, "BLE fail");

    //  Show the display.
    display::show()
        .expect("DSP fail");

    //  Test the touch sensor.
    touch_sensor::test()
        .expect("TCH fail");

    //  Mynewt event loop
    loop {                            //  Loop forever...
        os::eventq_run(               //  Processing events...
            os::eventq_dflt_get()     //  From default event queue.
                .expect("GET fail")
        ).expect("RUN fail");
    }
    //  Never comes here
}