On Mon, 30 Sep 2002, tomasz motylewski wrote:
> I do the following: knowing the sample rate and the current position of the HW
> pointer (via snd_pcm_avail_update - why there is no function which would tell
> me directly that - the current position in the buffer?) I can calculate when
> the required position _will_ happen. So I can just schedule the timer or sleep
> until that time. When it arrives I can check again snd_pcm_avail_update to see
> whether my calculation way correct and adjust the sleep period.
>
> I do not understand why ALSA drivers (or at least some plug-ins) could not do
> the same?
What same? Offer position in ring buffer?
> There is also another problem: I understand that snd_pcm_avail_update does not
> really read current count from the card, but uses a value stored in memory. So
> it will only be updated when the card generates an interrupt. Is there any way
> to force snd_pcm_avail_update or to use another function which will for sure
> query the HW and not use the cached value? If the card does not have a
> capability to report it, this could be extrapolated from the last time sample
> counter was updated and the current time.
Use snd_pcm_status() to get the accurate timing information. The
avail_update function is light version which does not need a context
switch between user and kernel space.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project http://www.alsa-project.org
SuSE Linux http://www.suse.com
-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf
_______________________________________________
Alsa-devel mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/alsa-devel
