a2dp Breaks Connectability of Other Bluetooth Device

[Fredrum]

Hello!! I am still learning about all this bluetooth and sound stuff so apologies if this is not the right place to ask this question!

The basic problem is that I can get my bt headphones (Apple AirPods) to work and I can get my bt game controller (Sony DS4) to work but I can't get them both to work at the same time.

I'm using a RaspberryPi4, RaspbianOS 32bit, Kernel 5.4 and 5.10 tested. Using bluealsa from standard apt install. PulseAudio is un-installed.

I believe I have narrowed it down to being something to do with a a2dp plugin.

I have read and followed a lot of help pages on the web but nothing has made a difference to this problem. I have re-flashed my RPi4 sd card twice to start over.

When I do the following it BREAKS Sony game controller bluetooth connectability. But make the Bluetooth Audio Headphones connect fine.

sudo nano /etc/systemd/system/bluetooth.target.wants/bluetooth.service to.... ExecStart=/usr/lib/bluetooth/bluetoothd --noplugin=sap --plugin=a2dp

And the following BREAKS the Bluetooth Audio Headphones connectability. But makes the Sony game controller connect correctly.

sudo nano /etc/systemd/system/bluetooth.target.wants/bluetooth.service to.... ExecStart=/usr/lib/bluetooth/bluetoothd --noplugin=sap

I can still 'Register' and 'Pair' both devices at all times. It's the final 'Connection' that fails.

Does anyone know what this might mean and how I could get both devices to work at the same time?

Cheers!

[borine]

Using bluealsa from standard apt install.

The Raspbian/RaspiOS bluealsa package is very old - you would need to contact The RaspiOS team to get support for it. So many changes have been made here since then, that realistically the best advice I can give to fix issues with it is to build from source. Having said that, I am surprised that you would add --plugin=a2dp to the bluetoothd command line. That tells bluetoothd to load only the a2dp plugin -its unlikely to be what you really want. Bluetoothd supports A2DP automatically, provided some service such as bluealsa has registered itself to implement it. Sounds to me like you have bigger issues than just an out-of-date bluealsa package. So perhaps you should first report the issue to a Raspberry Pi forum to see if there is some specific issue with their bluetooth package or configuration. If they cannot help, then perhaps build bluealsa from source with debug enabled, follow the guidance on the wiki here, and report back here any issues with debug logs.

BTW If you are using the Desktop or Full image that includes pulseaudio, it might be worth testing with pulse first, as that is how their system is now designed. If pulse works correctly then at least you know that the bluetooth stack is set up correctly before beginning to investigate bluealsa.

[Fredrum]

Hi and thanks for the pointers! I'm using this with a 'Retropie' image and they say that they only support sound over ALSA so I abandoned my pulseaudio exploration. I also posted on the Raspberry forums but there has been no reply yet. There's many posts about BT problems so not sure if they have people with the right experience. It sounds like I want to try to build a new version then. As if I remove the '--plugin=a2dp' flag then bt headphones won't do the Connect step. Not sure when I'll be able to get to the rebuild as there seems to be quite a few dependencies needed but I'll post back here with results if I do.

[borine]

if I remove the '--plugin=a2dp' flag then bt headphones won't do the Connect step.

That surely means something is wrong. That's not how it is supposed to work with Bluez 5. I would also recommend to remove the pairing info (bluetoothctl remove) before doing any new test just to make sure that pairing has happened with your current build of bluealsa and install of bluetooth, and that any errors caused by previous setups are not remaining in the bluetoothd database.

[borine]

Thinking again about this issue, the symptoms you report could result if the DS4 driver or service registers itself as an A2DP endpoint, because that would then prevent bluealsa from doing so. Starting bluetoothd with --plugin=a2dp disables support for bluetooth input devices, so the DS4 service fails to start, allowing bluealsa to become the A2DP endpoint.

[Fredrum]

Hm interesting even if I don't fully follow yet I'll have to re-read some more times I think. I stumbled on something that made it work for me without trying to build bluealsa from source. You can see my personal wip step-by-step here and see if it matches your theory. https://github.com/Fredrum/retropiescripts/wiki/Bluetooth---Both-Controllers-and-Audio

The DS4 controller actually receives Audio over Bluetooth when used with the actual PS4 game console. But no driver I'm aware of have managed to do this on any other OS/system. I believe Sony uses a custom protocol for the audio stream, something like that.

You can check out the Linux driver (by Sony) that I run for my DS4 controller, https://github.com/torvalds/linux/blob/master/drivers/hid/hid-sony.c

EDIT, changed "The DS4 controller actually transmits" to
"The DS4 controller actually receives"

[borine]

Thanks for the update. So my theory about DS4 registering A2DP was wrong.

Your connection problems are likely related to the Raspbian GUI bluetooth applet. #445 reported a similar problem. So using bluetoothctl for connect/disconnect, as you are now doing, is probably the best solution.

Changes made to ~/.asoundrc while an application is running will not normally be visible to that application, whether that is an issue for you depends entirely on your use cases. I have written some notes on using bluealsa as the ALSA "default" PCM device in a wiki article here: https://github.com/Arkq/bluez-alsa/wiki/Using-bluealsa-as-default-ALSA-PCM

[borine]

I believe Sony uses a custom protocol for the audio stream

Please can you post the output of

bluetoothctl info xx:xx:xx:xx:xx:xx | grep UUID

where xx:xx:xx:xx:xx:xx is the bluetooth address of the DS4. That will tell which profiles are supported (and can be connected). We are looking for UUID: Audio Sink (0000110b-0000-1000-8000-00805f9b34fb) which tells us that bluez has recognized it as an A2DP sink.

[Fredrum]

I only get these two,

UUID: Human Interface Device... (00001124-0000-1000-8000-00805f9b34fb) UUID: PnP Information (00001200-0000-1000-8000-00805f9b34fb)

Thank you for the "default" link. For now it seems to be working in Retropie just swapping the symlink around but I'll look into it as maybe is a better solution.

I'm not 100% sure the fault is in the Raspi BT gui app as I had the same problem before using just 'bluetoothctl'. Having said that I need to continue distilling my setup process as that's probably not as minimal as I can get it yet and that might shed some more light.

(just a reminder, I'm not trying to get the Audio on the DS4 to work, I'm using regular BT headphones for that. I'm not holding any hopes that I'll crack that nut)

[borine]

This issue appears to have been resolved as described in https://github.com/Arkq/bluez-alsa/issues/478#issuecomment-896510781

Closing.