11 New Device Tutorial
vanous edited this page 2 months ago

Supporting a new device in Gadgetbridge

This is a step by step tutorial for supporting a new device in Gadgetbridge. There are some differences depending on the transport layer being used (Bluetooth Classic, Bluetooth LE, WiFi, …), but most of it is independent of that. The tutorial only covers the basics to get you started quickly. For more details, have a look at the existing implementations for other devices. Try to do your implementation in a similar way (where it makes sense), so as to ease maintenance.

Before you start - some interesting articles about BLE device communication discovery: https://medium.com/@arunmag

See Appendix: Infrastructure for some general implementation topics and Developer-Documentation for an overview into Gadgetbridge’s inner workings and important classes.

Before going into the details, let’s have a short look at the process the user has to go through in order to connect a new device.

Start Device Discovery
  -> Select one of the displayed devices

-> If necessary: pair/authenticate with the device
  -> If necessary: provide certain settings like nick name, age, height, ...
    -> Initialize the device
      -> Device can be used

For this tutorial we will add support for the exemplary SuperBand 4000 device, so many things are named after that.

Part 1: Discovery

The first part deals with discovering SuperBand 4000 devices and telling Gadgetbridge that/how they are supported.

  1. Add a new device type constant SUPERBAND_4000 to nodomain.freeyourgadget.gadgetbridge.model.DeviceType. Pick a new number as the key and leave 10 numbers “room” to the last number. These are reserved so that related devices can have nearby numbers. Also specify a default icon (coloured) and a disabled icon (greyscale). If you don’t have any yet, reuse some other icons.
  2. Create a new package nodomain.freeyourgadget.gadgetbridge.devices.superband4000.
  3. In that package, create a class SuperBand4000DeviceCoordinator that extends nodomain.freeyourgadget.gadgetbridge.devices.AbstractDeviceCoordinator. This class tells Gadgetbridge whether a discovered device is supported and what features are supported (with the implementation in Gadgetbridge, not in general).
    1. Implement the method getDeviceType() and return the constant DeviceType.SUPERBAND_4000 that you previously added.
    2. Implement the method getManufacturer() and return the manufacturer name.
    3. If your device is a Bluetooth LE device, override the method createBLEScanFilters() and return a list of ScanFilters for recognizing your device during discovery by a Bluetooth service UUID for example. You can skip this if you cannot or don’t know how to recognize your device that way yet.
    4. Implement the method DeviceType getSupportedType(GBDeviceCandidate candidate). This method will be called during discovery in order to check wether the discovered device is supported by Gadgetbridge. To decide this, you might check further services, the MAC address, or even the device name if you don’t know a better way, yet. If you’re determined to support the given device candidate, you return the recognized DeviceType. Typically this is the one that you return in getDeviceType(). If you do not recognize the given candidate, return DeviceType.UNKNOWN so that another DeviceCoordinator can be asked.
    5. Implement getBondingStyle() depending on how your device needs to be paired on the Bluetooth level. Return BONDING_STYLE_BOND to perform BLE pairing, BONDING_STYLE_ASK to let the user decide that during discovery, or BONDING_STYLE_NONE to not perform BLE pairing at all.
    6. If your device needs some very special kind of pairing/bonding/authentication before it can be used, you may override the method getPairingActivity() in which you return an Activity class that will be shown for your device after the device discovery process. Otherwise, just return null.
    7. There are several more methods that you need to implement, mostly supportsXXX() where XXX is a certain feature a device may support or not. As soon as you implement support for one such feature, make sure to announce it by returning true in the corresponding supportsXXX() method. Otherwise the feature will not be available in Gadgetbridge.
  4. Register your SuperBand4000DeviceCoordinator class with nodomain.freeyourgadget.gadgetbridge.util.DeviceHelper#createCoordinators() so that it will be used.

So, that was the first part. With these changes, Gadgetbridge should be able to find and display your device in the Discovery view. If that is not the case, add breakpoints in your device coordinator’s getSupportedType() method to find out why. Also check the ScanFilters, if any. Only once your device is found and displayed during discovery, does it make sense to continue with the next steps.

Part 2: Communication

The next part deals with the communication between Gadgetbridge and your device. This part is very specific to the device and the communication protocol being used.

This code lives in a separate package because it is used by a contiuously running background Service. This service is the nodomain.freeyourgadget.gadgetbridge.service.DeviceCommunicationService.

  1. Create the package nodomain.freeyourgadget.gadgetbridge.service.devices.superband4000
  2. Create a SuperBand4000DeviceSupport class in that package. As the super class, choose one of the existing abstract classes like nodomain.freeyourgadget.gadgetbridge.service.serial.AbstractSerialDeviceSupport or nodomain.freeyourgadget.gadgetbridge.service.btle.AbstractBTLEDeviceSupport, depending on the transport layer.
  3. Edit nodomain.freeyourgadget.gadgetbridge.service.DeviceSupportFactory#createBTDeviceSupport() and add the code to instantiate your support class for DeviceType.SUPERBAND_4000.

Bluetooth Classic

For Bluetooth Classic with AbstractSerialDeviceSupport as super class, you will usually create at least two other classes: a SuperBand4000IOThread and a SuperBand4000Protocol.

  • The *IOThread class manages the Bluetooth rfcomm socket in a non-blocking way for callers.
  • The *Protocol class understands and handles the incoming and outgoing messages.

Bluetooth LE

For Bluetooth LE, you will use the nodomain.freeyourgadget.gadgetbridge.service.btle.Transaction and nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEQueue classes to communicate with the device via GATT events. Theses classes will take care of synchronizing everything.

See the subclasses of nodomain.freeyourgadget.gadgetbridge.service.btle.profiles.AbstractBleProfile for some ready-to-be-used implementations of standard BLE services/profiles.

Final Words

We hope that this tutorial will help you get started with adding support for new devices in Gadgetbridge.

For questions and improvements, do not hesitate to contact us!

Happy hacking,
the Gadgetbridge Team