Limits on BLE Audio ISO Broadcast Streams nRF5340 Audio DK

[Simon32]

Hello,

I am conducting a feasibility study on implementing Auracast capabilities using the nRF5340 Audio DK with nRF Connect SDK v2.9.0. My goal is to investigate the potential for broadcasting multiple audio streams. I want to understand the constraints and possibilities of the number of Broadcast Isochronous Groups (BIGs) and Broadcast Isochronous Streams (BIS) that can be supported.

I am currently able to stream 2 BIGs with 4 BISes per BIG. I do this using the nrf_auraconfig sample and use pre-encoded LC3 files from an SD card as the audio source, since for now my primary focus is on channel limitations and not real-time encoding.

When increasing the BIG count, I encounter a BUS FAULT and when increasing the BIS per BIG, I get an MPU FAULT. I understand that the nrf_auraconfig sample is designed for a maximum of two BIGs with four BIS streams each, but I am investigating whether these limits are soft constraints or hardcoded architectural limitations.

My questions:

1. Are the BIG and BIS limitations in the SoftDevice Controller defined by hardware/resource constraints, or are they configurable within the stack?

2. Are there specific SoftDevice or Zephyr stack configurations that could help extend these limits?

3. Has there been any update to the controller since the 6-streams discussion that could allow for more streams?

Understanding these constraints will help me with evaluate the feasibility of using Auracast. Any insights or recommendations would be greatly appreciated!

Thanks!

[Hieu]

Hello Simon32,

Could you please share what kind of requirements you are having?

1. Are the BIG and BIS limitations in the SoftDevice Controller defined by hardware/resource constraints, or are they configurable within the stack?

There is a hard limitation with airtime. Thus, it should be technically possible to add more streams if you reconfigure the streams to use less airtime, such as lowering bitrate, number of retransmits.

2. Are there specific SoftDevice or Zephyr stack configurations that could help extend these limits?

There are two relevant configurations, CONFIG_BT_ISO_MAX_BIG and CONFIG_BT_ISO_MAX_CHAN.

3. Has there been any update to the controller since the 6-streams discussion that could allow for more streams?

This conversation is most likely outdated. It was 2 years ago, when SoftDevice Controller doesn't support LE Audio yet. As you know, now it is the default controller for LE Audio in NCS.

When increasing the BIG count, I encounter a BUS FAULT and when increasing the BIS per BIG, I get an MPU FAULT. I understand that the nrf_auraconfig sample is designed for a maximum of two BIGs with four BIS streams each, but I am investigating whether these limits are soft constraints or hardcoded architectural limitations.

I suspect this is stack usage issue. Please try to increase them. Refer to https://github.com/nrfconnect/sdk-nrf/blob/v2.9.1/samples/bluetooth/nrf_auraconfig/prj.conf#L17-L19.

Hieu

[Simon32]

Hello Hieu,

Thanks a lot for your reply. 

My main requirement is to support multiple audio channels for different languages in a conference setting, using Auracast. The goal is to broadcast several simultaneous streams that participants can select from individually.

At this stage, I'm focusing purely on evaluating how many BIS/BIGs I can handle on the nRF5340 Audio DK using pre-encoded LC3 files from an SD card. Real-time encoding isn’t a priority yet. But I expect this will become relevant later, so I might come back with questions at that point.

Thanks again for pointing out the airtime constraints and the relevant configuration options. I applied those changes and already managed to increase the number of streams beyond what I initially had. I’ll keep experimenting with airtime, bitrate, and retransmit settings to see how far I can push it.

Appreciate the guidance!

Regards,

Simon

[Hieu]

Hi Simon,

It's good to hear things are working. I will close this case then, but please feel free to reopen it if you have a question on the same topic.

Regards,

Hieu