How to use nrf5340 as a USB Microphone device?

[RashmiV]

I want to use nrf5340 as a USB Audio Microphone.

I am taking the help of zephyr/samples/subsys/usb/audio/headphones_microphone sample app, which contains USB Headphone + USB Microphone.

To disable USB Headphone, I am commenting hp_dev related code from main.c and I am modifying the nrf5340dk_nrf5340_cpuapp.overlay as follows:

&usbd {
mic_0 {
label = "MICROPHONE";
compatible = "usb-audio-mic";
feature-mute;
channel-l;
channel-r;
};
};

I have a static 192 byte PCM buffer that I want to continuously send over USB, for which I am using the following code in loop:

struct usb_audio_dev_data *audio_dev_data = mic_dev->data;
struct net_buf *buffer = net_buf_alloc(audio_dev_data->pool, K_NO_WAIT);
memcpy(buffer->data, pcm_buffer, buffer_len);
ret = usb_audio_send(dev, buffer, buffer_len);

But it does not work and the code crashes. 

Please advise.

[ovrebekk]

Hi

You mean you run the code in a loop as fast as possible?

Then you will eventually run out of net_buffers, or fill up the USB buffers. 

Are you checking the return codes from net_buf_alloc(..) and usb_audio_send(..) to see if they return any errors?

I would recommend registering the data_written_cb callback in the hp_ops setup, so that you get a callback whenever an audio packet is successfully sent over the USB interface. Then you can use this to schedule the next update.

Best regards
Torbjørn

[RashmiV]

Hi, t

Thanks, I handled the buffers so that they don't fill up, and also wrote the data_written_cb. Within this callback, I am sending 192 bytes of audio data by calling usb_audio_send() again so that data is sent continuously after each successfully data_written_cb call. I can now see the Zephyr USB audio sample listed in the Audio Input devices of the host device. But I can not hear any sound on my host device. I tried sending a 400Hz sine wave, 600Hz sine wave, and also a 1 sec sample of a song (192k sized buffer), but I cannot hear any of those on the host default speaker. I captured the incoming USB data on the host device using wireshark, and it looks like the buffer that I am sending is getting received at the host side. But I am also seeing this error on wireshark :
USB isodesc 0 [Protocol error (-EPROTO)] (192 bytes)
Status: Protocol error (-EPROTO) (-71)

One USB packet as captured on wireshark is as follows:

00 de e9 93 00 88 ff ff 43 00 88 78 02 00 2d 00 .Þé...ÿÿC..x..-.
c6 be 2b 61 00 00 00 00 8d c3 01 00 00 00 00 00 ƾ+a.....Ã......
c0 00 00 00 d0 00 00 00 00 00 00 00 01 00 00 00 À...Ð...........
01 00 00 00 82 01 00 00 04 02 00 00 01 00 00 00 ................
b9 ff ff ff 00 00 00 00 c0 00 00 00 00 00 00 00 ¹ÿÿÿ....À.......
00 08 00 00 3c aa e3 59 b3 52 bf e7 36 fe aa 62 ....<ªãY³R¿ç6þªb
29 be 72 55 fc 11 e4 55 ec 66 62 66 b4 0f 29 cc )¾rUü.äUìfbf´.)Ì
e5 de ea a0 26 b9 8a 00 2b ff 61 43 06 d1 ed 00 åÞê &¹..+ÿaC.Ñí.
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 01 00 00 a8 04 2e 03 20 00 00 c0 00 04 ......¨... ..À..
2e 03 20 10 e2 07 8d b6 09 a5 f8 7b 56 8e f6 e0 .. .â..¶.¥ø{V.öà

What could be wrong?
Let me know if you want the entire wireshark capture, or want to look at the code.

[Jeffrey Haynes]

Are you able to post your code?  This seems like a reasonable approach but so far I haven't been able to get it to work without errors.

[upasna maurya]

Hi RashmiV

Actually I want to work on the  samples/subsys/usb/audio/headphones_microphone project. and need a help from you that which hardware you used for the usb microphone and usb headphone to interface with the nrf5340 dev kit? 

[ovrebekk]

Hi

It's more than 3 years since Rashmi posted in this ticket. If you are having issues I would recommend opening a new ticket, and include a summary of what you have tried and the issues you are facing, and we can have a look at it. 

Best regards
Torbjørn

[Sunil vignesh]

Hi ovrebekk ,I want to replicate exactly what you did with a USB microphone to send PCM buffer and capture it in audacity. Could you share the source code to replicate?

[ovrebekk]

Hi 

I tried to locate the code I set up originally, but I couldn't find it unfortunately. It's been many years and at least one PC upgrade since then. 

I believe the essential step was to add the data_request_cb to the microphone device as I mentioned in my reply, and provide a data buffer here. This callback will occur over and over allowing you to keep the audio stream running. 

Best regards
Torbjørn