What is the impact of timestamp when nrf5340 audio sends data?

[LandyWang]

Hello,

I'm working on nrf5340 audio bis gateway sample.

The NCS version I use is v2.2.0, I know it's a very old version, but for some reason I can't update to the latest version yet.'

I have a question about the timestamp parameter in bt_audio_stream_send. Setting this value to 0 enqueues the ISO SDU in a FIFO manner. So what happens if it is set to a non-zero value?

I tried to set it to a non-zero value. As a result, the iso interval during transmission became a variable value from 1 ms to 6 ms, and the bis headset did not receive any data.

Why can't data be sent when the timestamp is set to non-zero value?

[AHaug]

I know it's a very old version, but for some reason I can't update to the latest version yet.'

For some reason as in "you can't disclose your reason for why not", or "your not able to"?

Since you're using NCS 2.2.0, you really should update to a newer version for Audio. We recommend v2.6, as you then will be able to use the Nordic Softdevice controller in the audio app.

Kind regards,
Andreas

[LandyWang]

Thank you for your suggestion.

I updated the SDK version to v2.6.0, and after changing the timestamp in iso_stream_send to a non-0 value, I did get different results from v2.2.0.

The iso interval during transmission becomes 10ms, and -EIO errors will continue to occur during the transmission process.

I think compared to v2.2.0, v2.6.0 may have done some error checks when the timestamp is a non-zero value, so the results will be different.

However, I still don’t quite understand the purpose of the timestamp parameter. What does it mean when it is set to a value other than 0? Is there any document I can refer to?

[AHaug]

Hi,

I've had a quick discussion with the Audio team and we believe that you should find an explanation for your questions here:

https://docs.nordicsemi.com/bundle/ncs-latest/page/nrfxlib/softdevice_controller/doc/isochronous_channels.html#providing_data

as well as checking the detail with simpler example in 

https://github.com/nrfconnect/sdk-nrf/tree/main/samples/bluetooth/iso_time_sync

Kind regards,
Andreas

[LandyWang]

Thanks for your assistance.

It helps me a lot.