nrf5340_audio demo doesn't work with 7.5ms frames

[cstjohn]

Hi,

I pulled the latest versions of nrfconnect/sdk-nrf (1bd98d8) and zephyrrtos (fcaa60a)

I modified the nrf5340_audio/prj.conf file:

@@ -6,6 +6,8 @@
 
 # nRF5340 Audio
 CONFIG_NRF5340_AUDIO=y
+CONFIG_AUDIO_SOURCE_I2S=y
+CONFIG_AUDIO_FRAME_DURATION_7_5_MS=y
 

I get I2S RX overruns on the gateway...

GW [00:00:51.358,612] <inf> audio_datapath: Drft comp state: INIT

--- 4 messages dropped ---

GW [00:00:51.384,124] <wrn> audio_datapath: I2S RX continuing stream

--- 3 messages dropped ---

GW [00:00:51.424,621] <wrn> audio_datapath: I2S RX continuing stream

--- 2 messages dropped ---

GW [00:00:51.440,368] <wrn> audio_datapath: I2S RX overrun. Single msg

--- 1 messages dropped ---

GW [00:00:51.464,355] <wrn> audio_datapath: I2S RX continuing stream

--- 4 messages dropped ---

GW [00:00:51.504,119] <wrn> audio_datapath: I2S RX continuing stream

--- 2 messages dropped ---

GW [00:00:51.510,864] <inf> audio_datapath: Drft comp state: CALIB

--- 1 messages dropped ---

GW [00:00:51.524,353] <wrn> audio_datapath: I2S RX continuing stream

... and audio decode errors on the headsets:

HL [00:00:48.180,999] <inf> audio_datapath: sdu_ref_us not from consecutive frames (diff: 12500 us)

HL [00:00:48.182,220] <wrn> audio_datapath: Decoded audio has wrong size

HL [00:00:48.192,382] <inf> audio_datapath: Drft comp state: INIT

HL [00:00:48.192,413] <wrn> audio_datapath: Decoded audio has wrong size

HL [00:00:48.193,115] <inf> audio_datapath: Drft comp state: CALIB

HL [00:00:48.200,988] <inf> audio_datapath: sdu_ref_us not from consecutive frames (diff: 12500 us)

--- 2 messages dropped ---

HL [00:00:48.221,008] <inf> audio_datapath: sdu_ref_us not from consecutive frames (diff: 12500 us)

HL [00:00:48.222,320] <wrn> audio_datapath: Decoded audio has wrong size

How should I enable 7.5ms frames for evaluation? From a cursory inspection of nrf5340_audio/src/audio/audio_datapath.c it looks like frames are assumed to be in multiples of 1ms.

Thanks,

Chris

[Karl Ylvisaker]

Hello Chris,

You are correct, everything in the nRF5340_audio application is currently made for and tested with using 10 ms frame size.
That is to say, 7.5 ms frame sizes are not tested by us, and so the existence of the CONFIG_AUDIO_FRAME_DURATION_7_5_MS kconfig could cause confusion, since the only mention of this not being tested is in the kconfig definition.
I will make an internal request to have the documentation point this out explicitly, to avoid any confusion.
Thank you for pointing this out! :) 

Best regards,
Karl

[cwhit]

Hi Karl,

I am also interested in using 7.5 ms frame sizes with the ADK. Is there a plan to add support for this?

Thanks,
Chris W.

[Karl Ylvisaker]

Hello Chris W,

We have listed it as an internal task but it is not on the roadmap and so it does not have a concrete date/timeline tied to it at this time. 

Could you elaborate on why you are interested in using 7.5 ms frames instead of 10 ms frames for your application? To my knowledge the 7.5 ms frame option is mostly relevant when adapting to Bluetooth Classic audio, is this the reason?

Best regards,
Karl