Help with multichannel High Speed USB audio device

Help with multichannel High Speed USB audio device

[Laurent .]

Dear list,

I made an embedded device that has a CODEC with 6 inputs connected to an ARM9
micro-controller that has an integrated high-speed USB controller.
Now, I need to write the USB code on that micro-controller so that i can capture those
channels in real-time at 24bits / 48 KHz with low latency (ie. sub 10ms), on a computer.

I only need my device to work with Linux, and if possible, I would like to avoid writing a device
driver on the Linux-side.

Is there already such a USB audio driver available that I could nearly use "as is" and to which
i would conform ?

Would you have some general guideline on how to write the high-speed USB device code ?

Would you have any comment on the following :

For simplicity, my device is going to be the "clock master" of the system since it is already has
the exact clock that drives the CODEC.
I will maintain a circular buffer of samples (well, frames of samples) coming from the CODEC.
Each time a new frame arrives, i put the samples in the buffer and increase a counter so
i know how many frames of samples I have in the buffer, ready to be sent.
Each USB micro-frame (125ms/8000Hz), I send all the bytes corresponding to the frames that
I have in the circular buffer.
In average, 6*3*48000/8000 = 108, but I presume that could jitter slightly, which should not
be a problem at all.

Thanks in advance,
Laurent

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Re: Help with multichannel High Speed USB audio device

[Clemens Ladisch]

Laurent . wrote:
> I made an embedded device that has a CODEC with 6 inputs connected to an ARM9
> micro-controller that has an integrated high-speed USB controller.
> Now, I need to write the USB code on that micro-controller so that i can capture those
> channels in real-time at 24bits / 48 KHz with low latency (ie. sub 10ms), on a computer.
> 
> I only need my device to work with Linux, and if possible, I would like to avoid writing a device
> driver on the Linux-side.
> 
> Is there already such a USB audio driver available that I could nearly use "as is" and to which
> i would conform ?

Yes, snd-usb-audio.

> Would you have some general guideline on how to write the high-speed USB device code ?

Just conform to the USB (2.0) and USB Audio (1.0) specifications.

> For simplicity, my device is going to be the "clock master" of the system since it is already has
> the exact clock that drives the CODEC.

So you'd use an asynchronous endpoint.


Best regards,
Clemens

Re: Help with multichannel High Speed USB audio device

[Laurent .]

----------------------------------------
> Date: Fri, 24 Jul 2009 11:12:48 +0200
> From: clemens@ladisch.de
> To: sid6582@msn.com
> CC: alsa-devel@alsa-project.org
> Subject: Re: [alsa-devel] Help with multichannel High Speed USB audio device
>
> Laurent . wrote:
>> I made an embedded device that has a CODEC with 6 inputs connected to an ARM9
>> micro-controller that has an integrated high-speed USB controller.
>> Now, I need to write the USB code on that micro-controller so that i can capture those
>> channels in real-time at 24bits / 48 KHz with low latency (ie. sub 10ms), on a computer.
>>
>> I only need my device to work with Linux, and if possible, I would like to avoid writing a device
>> driver on the Linux-side.
>>
>> Is there already such a USB audio driver available that I could nearly use "as is" and to which
>> i would conform ?
>
> Yes, snd-usb-audio.
>
>> Would you have some general guideline on how to write the high-speed USB device code ?
>
> Just conform to the USB (2.0) and USB Audio (1.0) specifications.
>
>> For simplicity, my device is going to be the "clock master" of the system since it is already has
>> the exact clock that drives the CODEC.
>
> So you'd use an asynchronous endpoint.
>
>
> Best regards,
> Clemens

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