On Mon, Jul 1, 2013 at 9:27 PM, Clemens Ladisch <clem...@ladisch.de> wrote:
> Ming Lei wrote:
>> On Mon, Jul 1, 2013 at 9:06 PM, Clemens Ladisch <clem...@ladisch.de> wrote:
>>> Ming Lei wrote:
>>>> I understand the latency is effected by packet count in one URB,
>>>> and it shouldn't be related with URB count,
>>>
>>> This is true only when capturing.  For playback, the latency is the
>>> length of the entire pipeline.
>>
>> For playback, every URB submitted is added into hw table
>> immediately, then the data will be played to speaker. I don't
>> understand why the latency is the entire pipeline.
>
> A submitted packet will be transmitted only after all the other packets
> in the pipeline have been transmitted.

Yes, that is always true since EHCI HW will send out data(packet) to
device one by one at the scheduled frame/uframe according to the
order of URB submitting , so the USB audio driver can submit URBs
in advance, can't it?

Also could you provide the typical time one URB in audio driver may
span?

Thanks,
-- 
Ming Lei
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