On Tue, 14 Mar 2023 12:04:43 +0100
David Kastrup <dak@xxxxxxx> wrote:
>Fons Adriaensen <fons@xxxxxxxxxxxxxx> writes:
>
>> On Mon, Mar 13, 2023 at 10:20:01PM +0100, Giso Grimm wrote:
>>
>>> Based on the measurements I have the impression that more is going on in the
>>> USB audio driver than just 1ms packages.
>>
>> I'd agree.
>>
>> When I use alsa_delay with 96/2 things are OK for around 10
>> seconds, then for another 10 s I get all sorts of weird values,
>> and finally a stable value that is a few tens of samples higher
>> than the original. This stable value is different each time
>> the test is run.
>>
>> For 48/2, I get unstable values for the first 10 seconds, then
>> a stable value that is again different each time.
>>
>> It almost looks as if something tries to adapt to the situation,
>> but not in a deterministic way.
>
>Possibly depends on your offset with regard to the timer interrupt when
>starting operations?
>
I did some reading on USB audio quite a long time ago, and from that this is
what I 'think' I understand:
Since USB2 full speed, it will try to fit up to 8 'packets' if it can into
it's 1mS time frame where as previously it was one-for-one. Presumably if you're
sending a continuous stream of suitably sized packets and are close to that
number, sometimes you'll get 8 but other times you'll only get 7
--
Will J Godfrey {apparently now an 'elderly'}
https://willgodfrey.bandcamp.com/
http://yoshimi.github.io
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.
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