[alsa-devel] snd_dummy on Centos - Redhat

Clemens Ladisch clemens at ladisch.de
Thu Sep 3 15:05:59 CEST 2009

Giovanni Maruzzelli wrote:
> Yes, CONFIG_PREEMPT* are probably different between the various
> kernels, and also the compiled kernel is tickless.
> But, this is a problem only with snd-dummy.

The interrupts of other drivers are based on the PCM stream clock, but
the snd-dummy driver has to emulate interrupts using the system timer,
so it is the only one affected by timer-related changes.

> What I would like, in the interest of users, is snd-dummy to be
> modified in a way that makes it working on the regular CentOS-RHEL
> kernels,

The driver relies on the kernel's system timer.  It might be possible
to rewrite it to use high-resolution timers, if the CentOS kernels
supports it.

It would be easier to try to change the constraints of the sound card
that snd-dummy tries to emulate; set USE_PERIODS_MIN to four or so,
and increase period_bytes_min to some value that is at least as large
as the numer of bytes per timer tick (with 2 channels and 16 bits at
48 kHz, there are 192000 bytes per second).


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