Bluetooth: Detect Event Using Bluez

Question

• We are trying to detect an event in C/C++.
• We are using Bluez on Linux as our Bluetooth Library.
• Our objective is to run an external script when that event is triggered.
• Specifically, we have a Motorola H730 headset, with a button on it, and we are looking to detect the press of that button.
• We have paired the bluetooth device(hcitool), and we can connect to it (bluez-test-audio), but would be interested in migrating that approach to C/C++.

• The output of hcidump when the device is connected and the button is pressed is:

  HCI sniffer - Bluetooth packet analyzer ver 2.2
  device: hci0 snap_len: 1028 filter: 0xffffffff

  HCI Event: Mode Change (0x14) plen 6
  status 0x00 handle 21 mode 0x00 interval 0
  Mode: Active
  ACL data: handle 21 flags 0x02 dlen 17
  L2CAP(d): cid 0x0041 len 13 [psm 0]
  < ACL data: handle 21 flags 0x00 dlen 14
  L2CAP(d): cid 0x0047 len 10 [psm 0]
  < ACL data: handle 21 flags 0x00 dlen 22
  L2CAP(d): cid 0x0047 len 18 [psm 0]
  < ACL data: handle 21 flags 0x00 dlen 22
  L2CAP(d): cid 0x0047 len 18 [psm 0]
  HCI Event: Number of Completed Packets (0x13) plen 5
  handle 21 packets 1
  ACL data: handle 21 flags 0x02 dlen 18
  L2CAP(d): cid 0x0041 len 14 [psm 0]
  < ACL data: handle 21 flags 0x00 dlen 14
  L2CAP(d): cid 0x0047 len 10 [psm 0]
  HCI Event: Number of Completed Packets (0x13) plen 5
  handle 21 packets 1
  HCI Event: Number of Completed Packets (0x13) plen 5
  handle 21 packets 1
  HCI Event: Number of Completed Packets (0x13) plen 5
  handle 21 packets 1
  HCI Event: Mode Change (0x14) plen 6
  status 0x00 handle 21 mode 0x02 interval 2048
  Mode: Sniff

• We've looked for the bluetooth documentation and haven't had much success.
  How can we detect a bluetooth event in C/C++ using Bluez?

Answer 1

I did something similar last year. The approach I settled on was using libdbus-c++ to generate c++ proxy objects/classes to communicate with bluez via dbus.

• Determine the bluetooth interfaces implemented by your headset. I used d-feet and explored the device when it was connected. You can manually control and read status from the headset here, this came in handy for debugging.
• Generate,find or create the dbus xml descriptions of the required interfaces. I did this manually by translating the api specification from the bluez api documentation to xml however I believe you could also create them by dbus introspection.
• Use dbusxx-xml2cpp to generate proxy objects
• Determine the callback that is called when your button is pressed
• Integrate proxy objects into your code as required

You will need to link your code to libdbus-c++ and have it install on the target too.

You can use the generated proxy objects to access the entire functionality of the headset, it may come in handy for a lot more than catching a button press!

Answer 2

hcidump as collected are the logs between device host and controller. Events are the ones which controller had send to device host and commands are the request/responses sends to device host.

Bluez programming guide : http://people.csail.mit.edu/albert/bluez-intro/