LE Audio and custom service

[RakeLund]

We have an application today using Bluetooth classic to stream sound and BLE for streaming sensor data (not a nordic chip). We are looking at the possibility of replacing the chip with a nrf5340 and using LE Audio for streaming audio. I found some forum posts describing related issues and I interpret is as it should be possible to do. 
RE: Mix BLE audio and custom BLE Characteristic
Extend ble acl on LE Audio headset

I have 2 nrf5340 audio DKs and have managed to modify the nrf5340 audio sample to add a custom service on the peripheral, but haven't yet been able to read that service on the gateway. Do you have any examples or guides on how to do this? The second forum post I linked to says you have tested running 2 ACLs internally, but I haven't been able to find any code examples or instructions on how to set it up. I guess the way I have done it I use the same ACL for both LE Audio communication and the custom service.

Also, would one central be able to have different audiostreams to several peripherals, or would that require several centrals?

[Amanda Hsieh]

Hi, 

Are you going to use CIS?

Here is an unofficial example which is based on NCS v2.3.0. Although it is not for the NCS latest version, it's a good reference for a start. It uses NUS to send dummy data between the gateway and earbuds. 

“Beware that this code/configuration is not fully tested or qualified and should be considered provided “as-is”. Please test it with your application and let me know if you find any issues.”

Regards,
Amanda H.

[RakeLund]

Thank you, I will look into the example.

Initially we will use CIS, but BIS might be relevant for a future application where we want to stream audio to several devices. Is it possible to send data from peripheral to gateway and stream audio from gateway to peripheral with BIS?

[Amanda Hsieh]

Hi, 

Yes, but please be aware that the maximum ACL link number is 2 for a central to connect peripherals while working with BIS. 

This is the test case https://github.com/nrfconnect/sdk-nrf/tree/main/tests/bluetooth/iso and modules https://github.com/nrfconnect/sdk-nrf/tree/main/tests/bluetooth/iso/modules 

-Amanda H.

[RakeLund]

I have done some digging and it seems that the activation of nus in this example is done by changing a config variable in prj.conf and that the code managing bluetooth is part of the network core firmware. Am I correct when I think I have to modify the audio controller that is running on the network core if I want to add my own custom service?

[Amanda Hsieh]

Hi,

RakeLund said:

Am I correct when I think I have to modify the audio controller that is running on the network core if I want to add my own custom service?

No, the services within the application are running on the app code. 

-Amanda H.

[RakeLund]

I have been testing this example with one gateway and one headset device running on 2 nrf5340 audio dk. If I try to increase the rate of messages I get a warning that messages are dropped. 
Does this just mean the logging module dropped the messages because it couldn't keep up, or are they actually not being received?
Do you have any experience with what kind of data rate is possible to achieve on the nus service when running LE Audio?