Am 23.05.2019 um 01:32 schrieb Michael Mrozek EvilDragon@openpandora.org:
On Mi, 2019-05-22 at 19:53 +0200, H. Nikolaus Schaller wrote:
Hi,
ALSA reports 7 output devices. Accessing some of them leads to a kernel lock.
Some are additional sound cards for:
- bluetooth audio
- LTE modem voice channel
These do not work if the respective clock is missing. This is not yet debugged and therefore never did work.
I'm a bit puzzled here. On all my Linux systems, the bluetooth audio volume controls only pop up when I have a bluetooth audio device connected.
Otherwise, they don't exist and are not listed in alsa or pulseaudio.
It may be possible to use the UART (HCI) to carry sound data. Our module has a hardware PCM link which we map/present as a second sound card.
The same should be the case for LTE unless the modem is initialized.
Is the TWL even needed for Bluetooth Audio / LTE?
No. Every driver can register itself as a sound card. The twl6040 is one with some (buggy) subchannels.
Then we add extra sound cards to access the hardware sound link for Bluetooth and LTE.
A fourth sound card is the HDMI audio.
I don't know how this works, but I always thought bluetooth audio is independent of the sound card in a system.
Here we have multiple sound cards.
At least, from what I found on the internet, bluetooth audio is not affected by the sound card and it also works without any soundcard built-in.
This hardware based sound interface is intended to be used togehter with AESS. Then, you can configure AESS to route LTE voice channel to Bluetooth and idle the main processor. This goes far beyond the simple case of a Bluetooth headset on a PC.