Tinkerboard on-board Bluetooth: Cannot connect more than one device at a time

tinker · December 4, 2020

Hello,

I have been experimenting with the bluetooth audio on my tinkerboard. The issue is both present on the last rockchip-next (4.1x I think) and the rockchip-current 5.8.18 kernel. I am using bluez and bluealsa.

The problem is specific to the onboard bluetooth, using an external bluetooth dongle (a cheap and old CSR Bluetooth 3.0 dongle from China) works as expected, I can even send audio to multiple devices simultaneously (quality is very bad, but thats a bandwidth problem).

As long as I just connect one bluetooth audio device everything is fine. I can have multiple paired, but disconnected, devices and as long as I connect and play and diconnect, things keep working. But as soon as I try to connect a second device, while another one is already connected (not even playing), the second device shortly shows up as connected in `bluetoothctl` (while the LED on the speaker itself stil shows not-connected) and about 10-20 seconds later the device shows up as disconnected and would not even reconnect unless switched on or off.

The error logged by bluetoothd / bluez (5.55-1) is

bluetoothd[15142]: profiles/audio/avdtp.c:avdtp_connect_cb() connect to 74:A3:xx:xx:xx:xx: Connection refused (111)

The connection process does not reach the bluealsa layer, I had similar problems when quickly testing with pulseaudio's bluetooth module.

My question:

Is there anywhere in the armbian tinkerboard configuration some hardcoded option to only connect to one device at a time? I cannot imagine this to be alimit of the on-board chip, Are there any config options for the HCI UART kernel driver?