Re: [alsa-devel] bandwidth issue with usb-audio in alsa

On 5/27/08, Kunal Singh kunal@singhkunal.com wrote:

Hi,

    I have some update on the issue which I had reported earlier. In my last e-mail, I had not mentioned that iPod is connected to the target through a USB (HS) Hub. When I connect the

same hub to my Desktop and read its configuration using "usbview" - I see that "interval" for this hub is mentioned as "256 msec". (I have two hubs and I get all the results same with both the hubs).

    With 36 URBs, the gap between two set of transactions is appx 220 msec (220+36 => 256). So, I am wondering

if the problem which I am seeing is because the external hub. I can not connect iPod directly to my target board, because this board does not support enough current (as needed by iPod).

Some USB 2.0 hubs are single TT (transaction translator). If the hub is single TT all low speed USB devices share that TT. The pause could be caused by other things using the TT.

USB audio, keyboards, older devices, all USB 1.0 all use the TT. Single vs multi-TT is the source of a most USB audio problems. Get a USB 2.0 hub that supports multi-TT. Of course the vendors don't specify on the box single or multi-TT. Search on the web or email their support group.

    Can some one suggest, where is the problem - is it with the host controller driver?

Regards, Kunal Singh

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Kunal Singh wrote:

Hi,

My Platform

I am trying to stream audio data from a USB-device (an iPod) to my arm-based embedded device (running kernel 2.6.23). The USB-device confirms to usb digital audio (subclass - streaming) class. The endpoint buffer size 196 bytes and transfer period is 1 msec. So, I should be reading data every msec.

Problem

I am facing some bandwidth issues. The data is not being captured fast enough.

I notice that once one set of URBs are captured (one set equal to MAX_URBS), there is a significant delay in capturing the next set of URBs.

 I have set MAX_URBS equal to 32.
 When I connect a USB-Analyzer and analyze the timings, I can see that

32 URBs are captured at a interval of 1 msec each. After that there is a break of around 250 msec. And then again 32 URBs captured in sequence.

  If I change the MAX_URBs to any other value N, N URBs get captured at

interval of 1 msec each, and then there is a break.

  Can some one suggest a way to improve this problem. Is there some

configuration or parameter which I can change, so that URBs get submitted fast enough? May be as soon as the old one has retired.

Thanks and Regards, Kunal www.singhkunal.com

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