Test using the Desktop Head Unit

The Desktop Head Unit (DHU) lets your development machine emulate an Android Auto head unit so that you can run and test Android Auto apps. The DHU runs on Windows, macOS, and Linux systems.

After you've installed the DHU, you can test your Android Auto apps by connecting your mobile device to it using one of the supported connection mechanisms described in Run the DHU.

To report bugs or request features related to the DHU, use the issue tracker.

Install the DHU

Follow these steps to install the DHU on your development machine:

1. Enable developer mode on a mobile device running Android 9 (API level 28) or higher, as described in Configure on-device developer options.
2. Compile and install your app on the device.
3. Install Android Auto on the device. If Android Auto is already installed, make sure that you are using the latest version.
4. In Android Studio, open the SDK Manager and navigate to the SDK Tools tab, then download the Android Auto Desktop Head Unit Emulator package.

The DHU is installed in the SDK_LOCATION/extras/google/auto/ directory.

1. On Linux or macOS systems, run the following command in that directory to ensure the DHU binary is executable:

   chmod +x ./desktop-head-unit
   

Additional steps for Linux

If you are running DHU version 2.x on a Linux system, you need to install some additional libraries. The DHU binary depends on GLIBC version 2.32 or above. You can check the GLIBC version of your system by running this command:

ldd --version

If the version is lower than 2.32, update GLIBC to 2.32 or above, which might require you to upgrade the OS to a version that is compatible with GLIBC 2.32 or above.

You must also install the libc++1 and libc++abi1 libraries. The installation procedure varies depending on your Linux distribution. For example, on Debian-derived Linux distributions, you can install the libraries with this command:

sudo apt-get install libc++1 libc++abi1

Install pre-release versions of the DHU

To get access to pre-release versions of the DHU, you can either use a preview version of Android Studio or change the update channel of your existing Android Studio installation to the beta channel.

Run the DHU

After you install the DHU, you can test your Android Auto apps by connecting your mobile device and workstation over USB. Run the DHU by connecting your mobile device to a development machine using either the Accessory Mode (recommended for DHU 2.x), or ADB Tunneling.

Connect using Accessory Mode

Android Auto supports connecting to DHU version 2.x with the Android Open Accessory (AOA) protocol, using the following command:

./desktop-head-unit --usb

By default, the DHU scans through the list of available USB devices and attempts to connect to the first compatible one. To target a specific device, include the device ID as part of the --usb command, as follows:

./desktop-head-unit --usb=[DEVICE_ID]

Connect using ADB Tunneling

This method requires setting up a connection to the Android Auto head unit server over Android Debug Bridge (adb). Follow these steps to set up tunneling and run the DHU:

1. Enable Android Auto developer mode if it is not already.

2. If the head unit server is not already running, open the overflow menu and select Start head unit server, as shown in figure 1.

   On the device, a foreground service appears in the notification area that indicates that the server is running, as shown in figure 2.

   

   Figure 1. Context menu with developer options.

   

   Figure 2. Notification that the head unit server is running.

3. In the Android Auto app, tap Previously connected cars near the top of the Settings and ensure Add new cars to Android Auto is enabled.

4. Connect the mobile device to the development machine using USB.

5. Make sure the mobile device has its screen unlocked so it can launch the DHU.

6. On the development machine, run the following adb command to forward socket connections from the development machine's port 5277 to the same port number on the Android device. This configuration lets the DHU connect to the head unit server running on the mobile device over a TCP socket.

   adb forward tcp:5277 tcp:5277
   

7. Start the DHU by running the command desktop-head-unit.exe on Windows, or ./desktop-head-unit on macOS or Linux, from the SDK_LOCATION/extras/google/auto/ directory:

   cd SDK_LOCATION/extras/google/auto
   desktop-head-unit.exe # Windows
   ./desktop-head-unit # macOS or Linux
   

1. If this is the first time you are connecting the mobile device to the DHU, check the mobile device's screen to accept the terms of service and adjust permission settings as needed.

After the DHU has started, you can use DHU console commands to run and test your app.

Command-line options

By default, the head unit server connects over port 5277. To override the host or port, use the --adb=<[localhost:]port> flag, as shown in the following example:

./desktop-head-unit --adb=5999

By default, the DHU emulates an Android Auto-compatible head unit with a touchscreen user interface. Simulate user touches by clicking the DHU with a mouse. To emulate head units that use a rotary controller for input, you can use the -i rotary flag, as shown in the following example:

./desktop-head-unit -i controller

When the DHU is in rotary-controller mode, you can use keyboard shortcuts to simulate controller operations. See the Rotary controller section for more details. In rotary controller mode, the DHU ignores mouse clicks. You must operate Android Auto with the simulated rotary-controller operations.

Other command-line options for DHU are listed in the following table:

DHU user guide

This section describes the features supported by the DHU and how to use them.

Commands are entered in the terminal window where you started DHU. Multiple commands can be run on the same line by separating them with ;.

System

Touch and touchpad

When touch or touchpad is enabled, clicking in the display window, for touch, or touchpad window, for touchpad, registers as a touch event.

For touch, simulate multi-touch by right-clicking the first finger location, then clicking and holding the right button for the second finger. The centerpoint of the two fingers remains fixed; moving the mouse lets you rotate them around the center, pinch in and out, or both.

For touchpad, click and hold the left button to scroll between different UI elements on the screen. Clicking the right button selects the element that has focus.

Rotary controller

The DHU has rotary controller support. When it is enabled, the following actions are supported:

• Clicking up, down, left, and right on the D-pad
• Rotating clockwise and counterclockwise
• Performing a rotation flick (five steps at once)
• Clicking down and back on the controller

The commands and key bindings are listed in the following table.

A scroll wheel on a mouse sends dpad rotate commands, and the middle mouse button click, usually the scroll wheel, sends dpad click commands.

Note that most cars have touch screens. Some cars have only rotary controllers, and some have a hybrid touch and controller. Cars can also support a touchpad, which can be used for map panning and text entry. Be mindful of these different configurations when simulating different vehicle head units.

Microphone

The DHU supports using a microphone for voice input or to play a pre-recorded voice track. For convenience, the following sound files for common voice commands are included with the DHU. These sound files are located in the SDK_LOCATION/extras/google/auto/voice/ directory.

To run an individual .wav file in the DHU prompt, use the following command:

mic play /path/to/filename.wav

The following table lists other microphone-related commands:

Sensors

The DHU supports simulating changes in the vehicle's sensor data with the following commands. To mock sensor data and send it to Android Auto, the corresponding sensors must be enabled with the configuration .ini used file when starting the DHU.

Day and night modes

The DHU supports simulating changing between day and night mode with the following commands and key bindings:

Focus management

The DHU supports simulating whether or not Android Auto has focus on the head unit using the following commands:

Restrictions and driving status

The DHU supports simulating certain restrictions when the vehicle is moving, such as disabling the keyboard and disallowing phone configurations, using the following commands:

Instrument cluster

The DHU supports emulating an instrument cluster. This cluster is usually behind the steering wheel, and it shows basic information during navigation about the next turn—such as the next road name or a turn arrow—distance, or time. It also displays information about ongoing phone calls.

This can be enabled using the instrumentcluster entry in the [general] section of the configuration file, or by the navcluster or phonecluster entries to control each feature separately.

[general]
...
instrumentcluster = true

Cluster Display

Some vehicles have cluster displays capable of displaying rich visual information such as map tiles. Starting with version 2.1 of the DHU (currently available using the Android Studio Beta update channel ), you can emulate such a display on your development machine.

This can be done using a configuration file with a cluster [display] section. [display] sections support the same video configuration options as the main display configured in the [general] section of the file.

...

# The display name following the colon can be whatever you like.
[display:cluster]
# Setting the displaytype as cluster is what lets the DHU know how to handle it.
displaytype = cluster
resolution = 800x480
dpi = 160
...

This configuration can either be added directly to an existing .ini file or you can reuse it by putting it in a separate file and passing multiple configuration files when launching the DHU. When using multiple configuration files, later definitions of a given value override earlier ones.

# Launch your landscape configuration with your cluster display configuration
./desktop-head-unit -c landscape.ini -c cluster.ini

# Launch the portait configuration with the same cluster display configuration
./desktop-head-unit -c portrait.ini -c cluster.ini

Media Playback Status

The DHU supports an additional information display to show media playback status, such as what track is playing.

This can be enabled using the playbackstatus entry in the [general] section.

[general]
...
playbackstatus = true

Keycodes

The DHU provides a set of default keycodes that simulates the set of shortcut buttons that are commonly available in vehicles. For example, the home keycode can be triggered in the DHU prompt as follows:

keycode home

The following table lists other available keycodes:

Configure the DHU

The DHU supports a configuration .ini file to change the input modes between touch and rotary controller and to set the frame rate, resolution, and DPI the head unit requests from the phone.

The default location for the configuration file is ~/.android/headunit.ini. To change the configuration of the head unit on your system, you can modify this file.

You can also specify a configuration file to load using the -c flag:

./desktop-head-unit -c /path/to/config.ini

The following snippet shows a sample configuration:

[general]
touch = true
touchpad = false
controller = false
instrumentcluster = false
resolution = 800x480
dpi = 160
framerate = 30
fueltypes = unleaded,electric,hydrogen
evconnectors = supercharger

Sample configuration files that demonstrate different head unit settings you can test against are under the SDK_LOCATION/extras/google/auto/config/ folder. For more advanced use cases, please refer to the following supported settings.

Input configuration

The following table lists input configuration options:

Video configuration

Android Auto supports three video resolutions:

• 480p (800x480, the default)
• 720p (1280x720)
• 1080p (1920x1080)

To support other aspect ratios, the head unit can specify a margin to letterbox (pillarbox) as necessary. For example, if you want a 1000x600 screen, set the resolution to 720p (1280x720) and a marginwidth of 280 and marginheight of 120. This has the effect of adding a 140 px margin on the left and right edges and a 60 px margin on the top and bottom.

The following example configuration emulates a typical 6-inch screen (750x450):

[general]
...
resolution = 800x480
marginwidth = 50
marginheight = 30

And the following example configuration emulates a very wide screen:

[general]
...
resolution = 1280x720
marginwidth = 0
marginheight = 220

The following table lists other video configuration options:

Sensor configuration

To mock sensor data and send it to Android Auto, the corresponding sensors must be enabled using the following options. If a sensor is not enabled, any data sent for that sensor using the DHU commands is ignored. This configuration must be put in a [sensors] section, not in the [general] section used for most other config.

[general]
touch = true
...

[sensors]
location = true
fuel = true
...

Miscellaneous configuration options

The following table lists other configuration options:

Troubleshoot

Sometimes the DHU shows a blank screen when first connected. You can work around this by doing the following:

1. Close the DHU.
2. Follow step 5 described in Run the DHU to stop and restart the Head Unit Server.
3. Start the DHU again.
4. Grant any additional permissions requested on the phone screen. The DHU might shut down once more.
5. Restart the DHU if necessary.