From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
To: alsa-devel@alsa-project.org
Subject: usb: offset in trigger_tstamp?
Date: Thu, 20 Nov 2014 10:56:29 -0600 [thread overview]
Message-ID: <546E1D3D.50500@linux.intel.com> (raw)
In-Reply-To: <CAAgF-BfwGsn6HbJWH8uE48F2VWAYnAkv8=kGPkqCEWKaBM6=GQ@mail.gmail.com>
I was trying to find a bug in the timestamping logic I am working on and after some time I realized the USB audio class driver seems to have an issue.
If I instrument the code in sound/usb/pcm.c, I see a offset of up to 6ms between the snd_usb_substream_playback_trigger and prepare_playback_urb steps
[45053.102625] trigger_start
[45053.108320] prepare_playback_urb
My understanding is that empty URBs are submitted in the prepare step to avoid underflows, which is fine. The problem with that is that the trigger_tstamp value is captured before audio transfers actually start and there is a constant offset when trying to track audio/system time drifts or do basic a/v sync.
Any suggestions on how to fix this? I can't figure out if this is an off-by-one error or another bug.
Feedback welcome.
-Pierre
next prev parent reply other threads:[~2014-11-20 16:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-20 9:49 [PATCH] ASoC: samsung: In the i2s_set_sysclk() callback we are currently clearing all bits of the IISMOD register in i2s_set_sysclk. It's due to an incorrect mask used for the AND operation which is introduced in commit a5a56871f804edac93a53b5e871c0e9818fb9033 (ASoC: samsung: add support for exynos7 I2S controller) and also adds the missing break statement Padmavathi Venna
2014-11-20 9:49 ` Padmavathi Venna
2014-11-20 10:08 ` [alsa-devel] " Padma Venkat
2014-11-20 10:08 ` Padma Venkat
2014-11-20 16:56 ` Pierre-Louis Bossart [this message]
2014-11-21 13:28 ` usb: offset in trigger_tstamp? Clemens Ladisch
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