From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: Takashi Iwai <tiwai@suse.de>
Cc: Dylan Reid <dgreid@chromium.org>, alsa-devel@alsa-project.org
Subject: Re: [PATCH v2] ALSA: hda - Apply codec delay to wallclock.
Date: Thu, 11 Apr 2013 19:17:10 -0600 [thread overview]
Message-ID: <51676096.9000003@linux.intel.com> (raw)
In-Reply-To: <s5hvc7uh0we.wl%tiwai@suse.de>
>> For playback audio_timestamp = wallclk - codec_delay_in_nsec
>> for capture audio_timestamp = wallclk + codec_delay_in_nsec
>
> Hmm... I'm confused, too. From a pretty generic view,
>
> - hwptr = the samples (frames) transferred on the (memory) buffer
> - hwptr + PCM delay = the point being currently captured
>
> Which position does the wall clock correspond?
you now have 3 positions:
For capture:
hwptr = sample in memory
hwptr+ delay = sample recorded on link (tracked by LPIB and wallclock)
hwptr+ delay + codec_delay = sample recorded by A/D
For playback
hwptr = next sample in memory to be DMA'ed
hwptr - delay = sample pushed on link (tracked by LPIB and wallclock)
hwptr - delay - codec_delay = sample played in A/D
the wallclock is only at the soc/chipset level, it doesn't know anything
about the peripheral.
Makes sense?
-Pierre
next prev parent reply other threads:[~2013-04-12 1:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-09 1:20 [PATCH v2] ALSA: hda - Apply codec delay to wallclock Dylan Reid
2013-04-09 6:03 ` Takashi Iwai
2013-04-10 3:55 ` Pierre-Louis Bossart
2013-04-10 5:30 ` Dylan Reid
2013-04-10 14:29 ` Pierre-Louis Bossart
2013-04-10 15:16 ` Takashi Iwai
2013-04-12 1:17 ` Pierre-Louis Bossart [this message]
2013-04-12 8:55 ` Takashi Iwai
2013-04-13 8:55 ` Takashi Iwai
2013-04-15 8:02 ` Dylan Reid
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