nrf5340 audio:LE audio Stream stopped.INSUFFICIENT_RESOURCES

[Reskyllr]

We have an nrf5340 audio application, and there were no problems with the previous development.
But when I want to extend the CIS function, especially when enabling bidirectional transmission, an error occurs, but I cannot determine the reason.
00> HL [00:11:23.514,648] <inf> cis_gateway: Stream 0x20003744 stopped. Reason 13
00> HL [00:11:23.514,648] <wrn> cis_gateway: Unknown stream
00> HL [00:11:23.514,678] <inf> cis_gateway: Stream 0x20003524 stopped. Reason 13
00> HL [00:11:23.515,625] <wrn> cis_gateway: Unknown stream

Reason 13 is BT_HCI_ERR_INSUFFICIENT_RESOURCES.
What causes this error? If bidirectional transmission is not started, it works normally.
What I want to know most is what causes this error.

Thanks,

Reskyllr

[dejans]

Hi,

Support for bidirectional streams to or from 2 headsets was added in NCS v2.3.0. Have you selected CONFIG_STREAM_BIDIRECTIONAL=y in your project configuration?

Could you please provide information on what you try to achieve?

Best regards,
Dejan

[Reskyllr]

Hi dejans,

Yes, I added CONFIG_STREAM_BIDIRECTIONAL=y, I want to use CIS intercom functionality, but that's not my main goal.
I want to know what causes BT_HCI_ERR_INSUFFICIENT_RESOURCES.
Because there is another situation where the same error occurs:
I expanded the SDU size to 240 (used to transmit stereo sound) in BIS mode, and everything worked fine.
When I want to do the same work in CIS mode, Stream stop: Reason 13(BT_HCI_ERR_INSUFFICIENT_RESOURCES) appears.
If you restore the SDU size to 120 (mono transmission), it works normally.
But when adding CONFIG_STREAM_BIDIRECTIONAL=y, the same error (BT_HCI_ERR_INSUFFICIENT_RESOURCES) occurred again.

You don't need to understand it, I just want to know the cause of this error and how to fix it.
Thanks,
Reskyllr

[dejans]

Hi Reskyllr,

I have spoken to our developers. They have tested CONFIG_STREAM_BIDIRECTIONAL=y in prj.conf in the main branch and it seemed to be working without issues. Regarding SDU, it is not possible to put SDU to the value of 240 for bidirectional communication due to scheduling issues in a current version of the controller. The maximum size of SDU in each direction that is tested and expected to be working is 80.

Best regards,
Dejan

[Reskyllr]

Hi,dejans

I understand your statement.
In addition to SDU, it seems to be related to CONFIG_BT_AUDIO_RETRANSMITS.
When CIS SDU = 120, CONFIG_BT_AUDIO_RETRANSMITS=2, it works normally. CONFIG_BT_AUDIO_RETRANSMITS=4, BT_HCI_ERR_INSUFFICIENT_RESOURCES appears.
What is the conversion relationship between them? Do you mean that the two-way SDU needs to be limited to less than 80? Does it mean that the total SDU cannot exceed 160?