android open accessory protocol

Android Open Accessory Protocol

Android Open Accessory Protocol (AOA) is a protocol that allows Android devices to interact with external accessories over USB. This protocol enables Android devices to act as USB hosts, allowing them to communicate with a variety of accessories such as USB keyboards, game controllers, and even Arduino boards.

How it works

When an Android device is connected to an accessory that supports the AOA protocol, the device switches into accessory mode. In this mode, the accessory can communicate with the Android device using the Android Accessory Protocol, a set of messages that define how data is exchanged between the two devices.

To use the AOA protocol in your Android application, you need to request permission to communicate with USB devices and handle the USB connection events. Here is an example of how you can do this in your Android application:

// Request permission to communicate with USB devices
UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
UsbAccessory[] accessories = usbManager.getAccessoryList();
UsbAccessory accessory = (accessories == null ? null : accessories[0]);

PendingIntent permissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
usbManager.requestPermission(accessory, permissionIntent);

// Handle USB connection events
BroadcastReceiver usbReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (ACTION_USB_PERMISSION.equals(action)) {
            synchronized (this) {
                UsbAccessory accessory = (UsbAccessory) intent.getParcelableExtra(UsbManager.EXTRA_ACCESSORY);
                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if (accessory != null) {
                        // Start communicating with the accessory
                        // ...
                    }
                } else {
                    // Permission denied
                }
            }
        }
    }
};

AOA in action

Let's say you have an Android device and a USB game controller that supports the AOA protocol. When you connect the game controller to your Android device, the device switches into accessory mode and requests permission to communicate with the controller. Once permission is granted, your Android application can start communicating with the game controller and use it to control a game on the device.

Here is a journey diagram to visualize the process:

journey
    title AOA Communication Journey
    section Device connected
        Device->Accessory: Connection established
        Accessory->Device: Request permission
    section Permission granted
        Device->Accessory: Permission granted
        Accessory->Device: Start communication
    section Communication
        Device->Accessory: Send data
        Accessory->Device: Receive data

Flowchart

Here is a flowchart to summarize the process of using the AOA protocol in an Android application:

flowchart TD
    A[Request permission] --> B{Permission granted}
    B -->|Yes| C[Start communication]
    B -->|No| D[Permission denied]

In conclusion, the Android Open Accessory Protocol allows Android devices to communicate with external accessories over USB using a set of defined messages. By following the proper steps to request permission and handle USB connection events, you can integrate AOA functionality into your Android application and interact with a variety of accessories.