Re: Audio I/O parameters

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Alan Stern wrote:
> On Sat, 13 Jul 2013, Clemens Ladisch wrote:
>> James Stone wrote:
>>> On Mon, Jul 8, 2013 at 2:12 PM, James Stone <jamesmstone@xxxxxxxxx> wrote:
>>>>> configuring for 44100Hz, period = 64 frames (1.5 ms), buffer = 2 periods
>>>>> JackAudioDriver::ProcessAsync: read error, stopping...
>>>>
>>>> Some further info - on 3.5.0-28, I can start jackd in playback only
>>>> with 8 frames/period, and capture only at 16 frames/period.
>>>
>>> Any thoughts on further investigating this bug with the 3.8.0 kernel
>>> with the Focusrite Scarlett 2i4?
>>
>> Jack assumes that the interrupts for the playback and capture streams
>> happen at more or less the same time.  It might be possible that on the
>> newer kernels, there is a difference between the arrival times of the
>> first completion callback of each stream.
>
> The interrupts shouldn't differ by more than the duration of one URB,
> which would be 1 ms.  There is an initial delay when a stream is first
> started, which generally lasts 5-10 ms.  But I think that hasn't
> changed since the 3.5 kernel.  Would it make any difference?

The initial delay does not really matter as long as it's the same for
both streams.  (A difference of 1 ms would be significant if the period
size is that short.)

> Bear in mind that the input and output streams are started at totally
> different times.

Jack takes great care to start them together.

> And anyway, James's latest problem occurs even with playback only.

On my machine, 3 x 8 frames works, although Jack often complains that
two periods are already completed when it expected only one.  Anything
less (2 x 8 frames) does not work; and 8 frames is where even my PCI
card begines to make problems.

In any case, "poll timeout" would not indicate completion delays but
that no data was transferred _at all_.  In theory, this should not be
possible.  I'm stumped at the moment.


Regards,
Clemens
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