[pulseaudio-discuss] [REGRESSION] [PATCH] alsa: Disable timer-scheduling for PCMs with the BATCH flag

Raymond Yau superquad.vortex2 at gmail.com
Wed Mar 5 00:48:19 PST 2014

2014-03-04 21:59 GMT+08:00 Maarten Lankhorst <
maarten.lankhorst at canonical.com>:

> Hey,
> op 30-11-13 18:07, Lars-Peter Clausen schreef:
>> PCM Devices which have the BATCH flag set update the PCM pointer only with
>> period size granularity. Using timer based scheduling does not have any
>> advantage in this mode. For one devices which have that flag set usually
>> update
>> the position pointer in software after getting the period interrupt. So
>> disabling the period interrupt is not possible for this kind of devices.
>> Furthermore writing to or reading from the buffer slice for the current
>> period
>> is not possible since the position inside the buffer is not known. On the
>> other
>> hand the tsched algorithm seems to get easily confused for this kind of
>> hardware, which results in garbled audio output. This typically means
>> that timer
>> based scheduling needs to be manually disabled on systems with such
>> devices.
>> Auto disabling tsched in this case allows these systems to run with the
>> default
>> configuration.
> This causes a regression on USB headphones with winepulse when using
> pulseaudio 5.0.
> The latency is set to 100 ms and never changed afterwards, when
> interactive applications are
> run that require lower latency the latency is never lowered, and wine's
> dsound emulation will fail
> because it expects a granularity of ~40-50 ms at most, depending on the
> application.
> I believe that tsched can stay enabled, as long as we take care always to
> buffer at least 1 period_size.

if you disable timer scheduling , you have to specify
default-fragment-size-msec (period time) to 10 ms  if wine expect 10ms

; default-fragments = 4
; default-fragment-size-msec = 25

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