[alsa-devel] question about webcam audio capture

vichy vichy.kuo at gmail.com
Mon Sep 9 17:50:45 CEST 2013

hi Clemens:

2013/9/9 vichy <vichy.kuo at gmail.com>:
> hi Clemens:
> 2013/9/9 Clemens Ladisch <clemens at ladisch.de>:
>> vichy wrote:
>>> I try to do webcam audio capture on my arm platform.
>>> when I execute audio capture I got below message
>>> "retire_capture_urb: 108 callbacks suppressed"
>> This means that the retire_capture_urb() function printed lots of
>> messages, and that 108 of them were thrown away because they were
>> identical.
> Does that mean:
> 1. 108 of messages are the same and through away
> 2. alsa get data from uac device through Host controller driver 108
> times and find they are the same and through away
>>You have to look at the previous line to get the actual
>> message.
> I try to  grep -rwn '"retire_capture_urb.*' sound/usb/*, but get nothing.
> Would you please tell me what the "previous line to get the actual
> message"  you mean?
>>> 2. from usb mon log, it seems HW keep Active status high even until
>>> ehci_io_watchdog happen, because the ep status is  -EXDEV.
>> How are you trying to capture data?
> I use the capture function in tinyalsa.
forget to say, the command I execute is
tinycap record.wav -D 0 -d 0 -c 2 -r 32000

> BTW, If I want to use number of urbs I expected and only send/complete
> only 1 round, where I can find the source code to modify?
it seems ep->nurbs in snd_usb_endpoint_start is what I expected, right?


Thanks for your great help,

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