From: Clemens Ladisch <clemens@ladisch.de>
To: Alan Young <consult.awy@gmail.com>, alsa-devel@alsa-project.org
Subject: Re: Improving status timestamp accuracy
Date: Sat, 4 Jun 2016 12:17:23 +0200 [thread overview]
Message-ID: <84551786-d910-efa0-3cc7-23a3e8f6ed8f@ladisch.de> (raw)
In-Reply-To: <5752A005.2050309@gmail.com>
Alan Young wrote:
> I am looking at ways to get more accurate status timestamp information
> for various SoC drivers.
What for?
> A call to snd_pcm_status() result in snd_pcm_update_hw_ptr0() being
> called. This gets the current output position (pos) via
> substream->ops->pointer(substream) and then makes all the other
> calculations based on the result. In theory, the result of
> substream->ops->pointer() could be sample accurate but in practice it
> is very unlikely to be better than period accurate.
Accurate timestamps make sense only with accurate pointers. The purpose
of these timestamps is to allow better prediction of the position of the
DMA pointer, but this is pointless when the DMA pointer does large jumps.
Regards,
Clemens
next prev parent reply other threads:[~2016-06-04 10:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-04 9:31 Improving status timestamp accuracy Alan Young
2016-06-04 10:17 ` Clemens Ladisch [this message]
2016-06-04 10:43 ` Alan Young
2016-06-04 15:59 ` Clemens Ladisch
2016-06-04 16:20 ` Alan Young
2016-06-05 16:27 ` Clemens Ladisch
2016-06-05 16:32 ` Alan Young
2016-06-05 1:14 ` Raymond Yau
2016-06-05 10:33 ` Alan Young
2016-06-06 1:24 ` Raymond Yau
2016-06-06 9:40 ` Alan Young
2016-06-06 8:34 ` Takashi Iwai
2016-06-06 9:42 ` Alan Young
2016-06-06 14:53 ` Pierre-Louis Bossart
2016-06-07 6:44 ` Alan Young
2016-06-07 18:01 ` Pierre-Louis Bossart
2016-07-08 15:03 ` Alan Young
2016-07-15 20:13 ` Pierre-Louis Bossart
2016-07-19 15:33 ` Alan Young
2016-07-19 15:58 ` Pierre-Louis Bossart
2016-07-20 6:59 ` Alan Young
2016-08-01 21:56 ` Pierre-Louis Bossart
2016-08-02 7:30 ` Alan Young
2016-08-02 7:55 ` Clemens Ladisch
2016-08-02 16:25 ` Pierre-Louis Bossart
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