Introduction: The Power of Custom Android Things for IoT

Android Things, Google’s platform for embedded devices, offers a robust framework for building intelligent Internet of Things (IoT) products. While pre-built images are convenient, many advanced IoT projects, especially those requiring specific hardware integrations or a minimal footprint like a smart home hub, benefit immensely from a custom operating system image. This tutorial will guide you through the intricate process of building your own Android Things OS image, tailored to the precise needs of a hypothetical smart home hub project, from setting up your build environment to flashing your custom firmware.

Why Customize Your Android Things OS Image?

Customizing your Android Things OS image goes beyond mere preference; it’s a strategic choice for serious IoT development. Here’s why:

• Reduced Footprint: Remove unnecessary system apps and services, optimizing resource usage and boot times. This is crucial for resource-constrained embedded devices.
• Hardware Optimization: Integrate specific drivers for custom peripherals (sensors, actuators, displays) not supported by default images.
• Enhanced Security: Strip down potential attack surfaces by removing unused components and implementing specific security configurations.
• Branding and User Experience: Pre-install your smart home application, customize boot animations, and set default system behaviors for a seamless user experience aligned with your brand.
• Offline Capabilities: Optimize the OS for scenarios where internet connectivity might be intermittent or non-existent, crucial for local smart home operations.

Prerequisites and Setting Up Your Build Environment

Building an Android Things OS image requires a powerful Linux-based workstation (Ubuntu LTS is highly recommended) and specific software tools. Ensure you have:

• Hardware: A desktop/server with at least 16GB RAM, 200GB free disk space, and a multi-core processor.
• Operating System: Ubuntu 18.04 LTS or 20.04 LTS is ideal.
• Development Tools:
• Java Development Kit (JDK): OpenJDK 8.
• Android SDK Platform-Tools: ADB and Fastboot.
• Git for version control.
• Python 2.7.x or Python 3.x (depending on AOSP version).
• Essential build packages (see next step).
• Android Things Device: A supported development board (e.g., Raspberry Pi 3B+, NXP i.MX8M series) for flashing and testing.

Installing Essential Build Packages

Open your terminal and execute the following commands to install the necessary packages:

sudo apt-get update
sudo apt-get install git-core gnupg flex bison gperf build-essential zip curl zlib1g-dev gcc-multilib g++-multilib libstdc++6-4.8-dev lib32ncurses5-dev x11proto-core-dev libx11-dev libgl1-mesa-dev libxml2-utils xsltproc unzip m4 openjdk-8-jdk python

For newer Ubuntu versions, you might need to specify Python 2 if the build system expects it:

sudo apt-get install python-is-python2

Downloading the Android Things Source Code

The Android Things source code is part of the larger Android Open Source Project (AOSP). You’ll use the `repo` tool to download it. Create a working directory:

mkdir ~/android-things
cd ~/android-things

Initialize `repo` and download the source. For Android Things, we often target specific branches that support particular hardware. Let’s assume a generic branch suitable for a Raspberry Pi 3:

repo init -u https://android.googlesource.com/platform/manifest -b android-things-8.1.0_r0.2
repo sync -j8

The `repo sync` command will take a significant amount of time and disk space (over 100GB). Be patient.

Understanding the Android Things Build System

Android Things leverages the standard AOSP build system. Key components include:

• Manifests (.xml): Define which projects `repo` downloads.
• Device Trees (device/): Hardware-specific configurations (kernel, board files, HALs).
• Product Definitions (build/target/product/): Define the components, packages, and features included in a specific build variant.
• BoardConfig.mk & AndroidProducts.mk: Define board-specific settings.

To build, you typically use the `lunch` command to select a target and then `make` to compile the source.

Customizing Your OS Image for a Smart Home Hub

This is where the real magic happens. We’ll focus on modifying product configurations.

1. Creating a Custom Product Definition

Navigate to `device/google/rpi3` (or your target device’s directory). You’ll often find a `product` directory containing `.mk` files. We’ll create a new product based on an existing one.

cd device/google/rpi3/
# Copy an existing product definition as a base
cp rpi3.mk smart_home_hub.mk

Now, edit `smart_home_hub.mk`. Add a product name and inherit from the base Android Things product:

# device/google/rpi3/smart_home_hub.mk
PRODUCT_USE_IN_COMBO := true
PRODUCT_DEVICE := rpi3
PRODUCT_BRAND := SmartHome
PRODUCT_NAME := smart_home_hub
PRODUCT_MODEL := SmartHomeHub-01

$(call inherit-product, device/google/rpi3/rpi3.mk)
$(call inherit-product, device/google/at_base.mk)

# Add custom features here

2. Including Your Custom Smart Home Application

Let’s assume you have a pre-compiled Android APK for your smart home application (e.g., `SmartHomeApp.apk`). To include it, you need to place it in your source tree and define its inclusion in your product makefile.

First, create a directory for your prebuilts:

mkdir -p packages/apps/SmartHomeApp/prebuilt/
cp /path/to/your/SmartHomeApp.apk packages/apps/SmartHomeApp/prebuilt/SmartHomeApp.apk

Then, create a `Android.mk` file in `packages/apps/SmartHomeApp/`:

# packages/apps/SmartHomeApp/Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional
LOCAL_MODULE := SmartHomeApp
LOCAL_SRC_FILES := prebuilt/SmartHomeApp.apk
LOCAL_MODULE_CLASS := APPS
LOCAL_MODULE_SUFFIX := $(COMMON_ANDROID_PACKAGE_SUFFIX)
LOCAL_CERTIFICATE := platform
LOCAL_PRIVILEGED_MODULE := true # If your app needs system permissions

include $(BUILD_PREBUILT)

Finally, add `SmartHomeApp` to your `smart_home_hub.mk` to include it in the build:

# device/google/rpi3/smart_home_hub.mk (continued)
PRODUCT_PACKAGES += 
    SmartHomeApp 
    # Add other system apps you want to include

3. Removing Unnecessary Default Applications

To reduce footprint, you might want to remove default Android Things apps that aren’t relevant for a smart home hub (e.g., settings apps if you have a custom UI). You can achieve this by overriding `PRODUCT_PACKAGES` or using `PRODUCT_REMOVE_PACKAGES` in your `smart_home_hub.mk`.

# Example of removing a package
PRODUCT_REMOVE_PACKAGES += 
    Settings 
    WebViewGoogle 
    # ... other apps to remove

Be cautious when removing packages; ensure you don’t remove critical system components.

4. Customizing Boot Animation and Branding

For a branded device, you’ll want a custom boot animation. The boot animation files are typically in `frameworks/base/data/sounds/bootanimation`. You can replace `bootanimation.zip` with your custom animation, ensuring it follows the AOSP boot animation specification.

Building Your Custom Android Things OS Image

Once your customizations are in place, it’s time to build the image.

1. Set up the Environment

cd ~/android-things
source build/envsetup.sh

2. Select Your Product Target

Use `lunch` to select your custom product. The format is `product_name-build_variant` (e.g., `smart_home_hub-userdebug`).

lunch smart_home_hub-userdebug

If you get an error that the product is not found, ensure `smart_home_hub.mk` is correctly referenced and `AndroidProducts.mk` in `device/google/rpi3/` lists `smart_home_hub`.

3. Compile the Source

Start the build process. This will take several hours depending on your machine’s power.

make -j$(nproc)

Upon successful completion, your images (e.g., `boot.img`, `system.img`, `userdata.img`) will be located in the `out/target/product/rpi3/` directory.

Flashing Your Custom Image to the Device

With your custom OS image built, the final step is to flash it onto your Android Things device. Ensure your device is in fastboot mode.

1. Connect Your Device

Connect your Raspberry Pi 3 (or other target board) to your workstation via USB, ensuring it’s in fastboot mode. The method to enter fastboot varies by board (e.g., specific jumper settings or commands via serial console).

Verify fastboot connection:

fastboot devices

You should see your device’s serial number.

2. Flashing the Images

Navigate to your output directory:

cd out/target/product/rpi3/

Then, flash the images using `fastboot`:

fastboot flash boot boot.img
fastboot flash system system.img
fastboot flash userdata userdata.img
fastboot reboot

Some devices might require additional partitions or a full `fastboot update ` command if you build a flashable zip.

Verification and Testing

Once your device reboots, observe the boot sequence. You should see your custom boot animation (if applied). Once booted, verify your pre-installed smart home application is present and functions as expected. Check for system stability and resource usage to ensure your customizations haven’t introduced regressions.

Conclusion

Building a custom Android Things OS image for a smart home hub is a complex yet rewarding endeavor. It provides unparalleled control over your device’s software stack, enabling deep optimization, specialized hardware support, and a branded user experience. While this guide covers the core steps, the Android Things ecosystem offers a vast array of further customization possibilities, from kernel modifications to advanced security hardening. Embrace this power to truly differentiate your IoT solutions and bring your smart home vision to life.