Hello World!


The “Hello World” example (sometimes lovingly referred to as “Blinky”) is an end-to-end example that shows basic Moto Mods functionality (by controlling the LED on the Reference Moto Mod). It includes open source firmware and is driven by the MDK Utility app (see the MDK Utility Example page for more details, including Flashing & Developer support).

The purpose of this example is to:

  • Provide a “Hello World” example (aka “Blinky”)
  • Demonstrate end-to-end implementation of Moto Mods functionality
  • Provide control to LED located in Reference Moto Mod

Before you begin...

Required Hardware

This app and example requires a Moto Z and Reference Moto Mod. To get started, you'll need to buy the required hardware.

Learn More Buy Now

Software and Tools

See the Build > Tools section to set up your development environment and learn about building from source, flashing firmware, and how to debug & log.

Download Example Source Code

‘MDK Utility’ App

MDK Utility is a simple app that provides an end-to-end ‘Hello World’ example that shows how to control the LED on the Reference Moto Mod.

The MDK Utility App will only work on Moto Z devices.

For more details, see the Moto Mods Android Application section further down this page.

Community and Support

Ask questions, engage with the developer community, and get support for this example in the Moto Mods group at element14.com. Also check out our Support page.

Firmware Development


Follow these instructions to setup your firmware development environment and download source code if it has not been done already. The base source code has a target for blinky. The information below details the steps to create the firmware for blinky, if it did not exist before.

New Build Target

Create a new build target for blinky using hdk/muc/base_powered target as the base.

$ cd $BUILD_TOP/nuttx/nuttx/configs/hdk/muc
$ mkdir blinky
$ cp base_powered/* blinky/

Switch to using the new build target.

$ cd $BUILD_TOP/nuttx/nuttx/tools
$ ./configure.sh hdk/muc/blinky

The following features in nuttx are to be enabled to support blinky functionality.

  1. Greybus RAW protocol
  2. Timer 6

To integrate into menuconfig and the build system, two files must be updated.


    bool "Blinky LED Mods Raw support"
    default n
    depends on GREYBUS_RAW
    select DEVICE_CORE
    select STM32_TIM6
        Enable Blinky LED Raw support


CSRCS += stm32_modsraw_blinky.c

Raw Protocol

  • nuttx/drivers/greybus/raw.c - Raw protocol
Configuration Changes

Set the configuration options to enable Raw Protocol.

$ cd $BUILD_TOP/nuttx/nuttx
$ make menuconfig
Device Drivers  --->  
[*] Greybus support  --->
[*]   Vendor Raw Support


Set the configuration options to enable timer6.

$ cd $BUILD_TOP/nuttx/nuttx
$ make menuconfig
System Type  --->
STM32 Peripheral Support  --->
[*] TIM6

Blinking LED (Blinky) Device Driver

The driver implements blinking LED control with ON/OFF data exchange over raw protocol between Moto Z and the reference mod.

In addition the driver also toggles a control GPIO(to control optional external circuitry) based on the same blinky ON/OFF commands.

  • nuttx/configs/hdk/muc/src/stm32_modsraw_blinky.c - raw protocol device driver for blinking LED control.
Blinky Raw Protocol

Message format: (Table coming soon...)

Message Commands: data sent from apk to HDK 0 or ‘0’ for OFF command. Non-zero value for ON command.

Driver Details

stm32_modsraw_blinky.c This driver is based on nuttx/nuttx/configs/hdk/muc/src/stm32_modsraw.c

static struct device_raw_type_ops blinky_type_ops = {
    .recv = blinky_recv,
    .register_callback = blinky_register_callback,
    .unregister_callback = blinky_unregister_callback,

static struct device_driver_ops blinky_driver_ops = {
    .probe = blinky_probe,
    .type_ops = &blinky_type_ops,

struct device_driver mods_raw_blinky_driver = {
    .type = DEVICE_TYPE_RAW_HW,
    .name = "mods_raw_blinky",
    .desc = "Blinky LED Raw Interface",
    .ops = &blinky_driver_ops,

Setup the GPIO and initialize the pin in the driver.

In stm32_boot.c
{ GPIO_MODS_LED_DRV_3,     (GPIO_OPENDRAIN)             },

In stm32_modsraw_blinky.c 
static int blinky_probe(struct device *dev)
    gpio_direction_out(GPIO_MODS_LED_DRV_3, LED_OFF);
    gpio_direction_out(GPIO_MODS_DEMO_ENABLE, 0);
    return 0;

Implement raw message handling in blinky_recv(). Turn ON LED blinking with any non-zero value.

static int blinky_recv(struct device *dev, uint32_t len, uint8_t data[])
    if (len == 0)
        return -EINVAL;

    if (data[1] == 0 || data[1] == '0')

    return 0;

Initialize and setup timer functionality for the timer handler be triggered every 1000 milliseconds

#define BLINKY_ACTIVITY    10
#define BLINKY_TIM          6
#define BLINKY_TIM_FREQ  1000
#define BLINKY_PERIOD    1000

static void blinky_timer_start(void)
    gpio_set_value(GPIO_MODS_DEMO_ENABLE, 1);

        tim_dev = stm32_tim_init(BLINKY_TIM);


        STM32_TIM_SETMODE(tim_dev, STM32_TIM_MODE_PULSE);
        STM32_TIM_SETISR(tim_dev, blinky_timer_handler, 0);
        STM32_TIM_ENABLEINT(tim_dev, 0);

In timer handler function, toggle the GPIO level.

static int blinky_timer_handler(int irq, FAR void *context)
    new_val = gpio_get_value(GPIO_MODS_LED_DRV_3) ^ 1;
    gpio_set_value(GPIO_MODS_LED_DRV_3, new_val);


Disable the timer and assert the GPIO to stop the LED blinking

static void blinky_timer_stop(void)
        gpio_set_value(GPIO_MODS_DEMO_ENABLE, 0);
        STM32_TIM_DISABLEINT(tim_dev, 0);
        tim_dev = NULL;

        gpio_set_value(GPIO_MODS_LED_DRV_3, LED_OFF);

Driver and Device Initialization

MDK has LED connected over GPIO pin PE8 Define the GPIO for LED control at $BUILD_TOP/nuttx/nuttx/configs/hdk/muc/include/mods.h

#define GPIO_MODS_LED_DRV_3      CALC_GPIO_NUM('E',  8)

Control GPIO to enable/signal any external circuitry Define the control GPIO at $BUILD_TOP/nuttx/nuttx/configs/hdk/muc/include/mods.h


The device driver is initialized in $BUILD_TOP/nuttx/nuttx/configs/hdk/muc/src/stm32_boot.c.
Entry in the devices[] array.

        .type = DEVICE_TYPE_RAW_HW,
        .name = "mods_raw_blinky",
        .desc = "Blinky LED Raw Interface",
        .id   = 0,

Part of the board_initialize() function.

  extern struct device_driver mods_raw_blinky_driver;
Configuration Changes

Set the configuration options to enable the raw protocol device driver for Blinky.

$ cd $BUILD_TOP/nuttx/nuttx
$ make menuconfig
Board Selection  --->
Select target board (Motorola HDK MuC)  --->
[*] Blinky LED Mods Raw support

Hardware Manifest

New Manifest

Create hardware manifest for the example using apps/greybus-utils/manifests/hdk-powered.mnfs as the base.

$ cd $BUILD_TOP/nuttx/apps/greybus-utils/manifests
$ cp hdk-powered.mnfs hdk-blinky.mnfs

Edit the hdk-blinky.mnfs file to change the interface string and add Raw Interfaces and Bundle.

[string-descriptor 2]
-string = MDK-POWERED
+string = MDK-BLINKY
; RAW interface on CPort 4
[cport-descriptor 4]
bundle = 3
protocol = 0xfe

; RAW Bundle 3
[bundle-descriptor 3]
class = 0xfe
Setting the Manifest

Set the configuration options to use the newly created manifest.

$ cd $BUILD_TOP/nuttx/nuttx
$ make menuconfig
Application Configuration  --->
-*- Greybus utility  --->
Select a predefined Manifest (Custom manifest)       
(hdk-termapp) manifest name

Building and Flashing Firmware

The new target supports all required functionality now. The firmware can be built and flashed into the Reference Moto Mod. Make sure that the Moto Mod is running in development mode as per these instructions or build and flash the development bootloader yourself as documented here.

Moto Mods Android Application

MDK Utility sample APK

The MDK Utility sample APK is an open source project, works as an downloadable Android app, to show the capability to toggle the MDK LED.

Install APK

Download and install the MDK Utility sample APK - see MDK Utility app on Google Play Store

Source code

The source code of the MDK Utility sample APK is published at https://github.com/MotorolaMobilityLLC/mdkutility.

To build the sample APK from source code, please download and install Android Studio from Android Developer Site, then import the mdkutility project into Android Studio. See Setup Your Development Environment for more info.

Sequence Diagram

(Diagram coming soon…)


Reference for ModManager interface:
Intent service = new Intent(ModManager.ACTION_BIND_MANAGER);
bindService(service, mConnection, Context.BIND_AUTO_CREATE);

private ServiceConnection mConnection = new ServiceConnection() {

   public void onServiceConnected(ComponentName className,
                                  IBinder binder) {
       IModManager mMgrSrvc = IModManager.Stub.asInterface(binder);
       modManager = new ModManager(context, mMgrSrvc);

   public void onServiceDisconnected(ComponentName className) {
       modDevice = null;
       modManager = null;


Reference for ModService events:
/** Register Mod intents receiver */
modReceiver = new MyBroadcastReceiver();
IntentFilter filter = new IntentFilter(ModManager.ACTION_MOD_ATTACH);
* Request the broadcaster who send these intents must hold permission PERMISSION_MOD_INTERNAL,
* to avoid the intent from fake senders. For future details, refer to:
* https://developer.android.com/reference/android/content/Context.html#registerReceiver
context.registerReceiver(modReceiver, filter, ModManager.PERMISSION_MOD_INTERNAL, null);
Query Mod status:
List<ModDevice> l = modManager.getModList(true);
if (l == null || l.size() == 0) {
  Log.d(Constants.TAG, "Mod device invalid”);

for (ModDevice d : l) {
   Log.d(Constants.TAG, "Mod device Info: " + d);
Reference for ModManager RAW protocol:
List<ModInterfaceDelegation> devices =
if (devices != null && !devices.isEmpty()) {
   // TODO: go through the whole devices list for multi connected devices.
   // Here simply operate the first device for this example.
   ModInterfaceDelegation device = devices.get(0);

    * Be care to strict follow Android policy, you need visibly asking for
    * grant permission.
   if (context.checkSelfPermission(ModManager.PERMISSION_USE_RAW_PROTOCOL)
           != PackageManager.PERMISSION_GRANTED) {
   } else {
       /** The RAW_PROTOCOL permission already granted, open RAW I/O */
       return true;
Execute RAW command:
public static byte[] RAW_CMD_LED_ON = {0x01};
public static byte[] RAW_CMD_LED_OFF = {0x00};

// Turn ON LED
byte[] cmd = RAW_CMD_LED_ON;

// Turn OFF LED
byte[] cmd = RAW_CMD_LED_OFF;

1) Attach MDK to phone, then install and launch MDK Utility sample apk:
(Screenshot coming soon...)

2) Check the Mod / Personality card status and information, then turn on/off LED switcher UI to enable LED to blink:
(Screenshot coming soon...)

3) The LED light on board should blink.