Bluetooth Stack

btstack implements A2DP and SDP on top of L2CAP. The program communicates with a USB Bluetooth dongle using libusb. It sends HCI (host controller interface) commands and data as USB packets and receives the responses in the same way. This package contains two programs. One of them is the Bluetooth device daemon, which handles all connections to a given USB Bluetooth device. The other is an MP3 player which connects to the daemon and handles the A2DP stuff, as well as selecting the target Bluetooth speaker etc. Here is the package: This contains many external dependencies as well, such as db, libusb etc.

It's best to run this using the bundled script. There are several environment variables which must be set for it to work properly. There are no in-program settings, although I was planning to add some. I stopped working on it after I got my boombox working.

One of the settings not mentioned in the README file is the address of the target Bluetooth speaker. In order to find out this address, you need to configure the rest of the system and turn on debugging. When you first try to use the program, it will send out some query packets to discover what's available nearby. Your speaker/headphone will reply to these enquiries and the program will print its address when that happens. You then just need to copy/paste that address into the appropriate environment var.

The program has several shortcomings. First of all, it doesn't properly shutdown neither the connection nor the Bluetooth dongle. Therefore, you need to pair your speaker with the dongle every time you use it. You don't have to do anything special for this. Just turn on your speaker in pairing mode before using it.

Another consequence is that, when either the speaker or the dongle gets stalled for some reason, the system can't handle that gracefully. The only thing to do in this case is the following:

After that, you need to plug the dongle in and then turn on the speaker before you start the program again.

I tried to follow the Bluetooth specs as much as possible, but I had to leave out quite a bit. One thing not mentioned in the Bluetooth A2DP specification is the following: After you have made a control connection for A2DP with the remote device, you need to open a second connection on the same port (0x90?? I don't remember) in order to send audio data. This is not mentioned in the specs and can be found only on Internet forums.

If I can fix the shutdown problem and make a saner event system, the program is in fact quite decent. It could be useful for more stuff like Bluetooth keyboards etc. I wonder if BSD guys need some Bluetooth speaker support..


The first link is to a project also called btstack, but it's not mine. We got the same name by coincidence.

btstack - A Portable User-Space Bluetooth Stack - Google Project Hosting
lwalkera/lwBT · GitHub
A fork of the lwBT stack. Contribute to lwBT development by creating an account on GitHub.
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Architecture - btstack - Describes the overall architecture and how clients interact with the stack. - A Portable User-Space Bluetooth Stack - Google Project Hosting
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