Re: PulseAudio and SNDRV_PCM_INFO_BATCH

From: Raymond Yau <superquad.vortex2@gmail.com>
To: David Henningsson <david.henningsson@canonical.com>
Cc: Tanu Kaskinen <tanu.kaskinen@linux.intel.com>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Takashi Iwai <tiwai@suse.de>,
	clemens@ladisch.de,
	ALSA Development Mailing List <alsa-devel@alsa-project.org>,
	Arun Raghavan <arun@accosted.net>
Subject: Re: PulseAudio and SNDRV_PCM_INFO_BATCH
Date: Fri, 19 Jun 2015 09:17:08 +0800	[thread overview]
Message-ID: <CAN8cciaFQ-fRi1RL-1pL3CBjxjvekFs6eU=n7xpinpxJBo8Zog@mail.gmail.com> (raw)
In-Reply-To: <55818DB5.6050007@canonical.com>

> Hmm...I was trying to understand this power save argument. I tried to
figure out a "typical" URB size by just plugging my headset in, and I saw
wMaxPacketSize being 96 and/or 192 bytes.
> Then, MAX_PACKS is set to either 6 (or 48 for USB 2.0 devices, but this
is just a headset).
>
> Can this be correct? Does it mean that we are getting interrupts every
192 * 6 bytes (i e, every 6 ms for a 48kHz/stereo/16bit stream)?
>
>

Do this mean that the driver report exact one period only when period size
is multiple of wMaxPackerSize ?

Using other period size give bad result , the driver use variable  period
size

hw_ptr does not always at period boundary , seem more like DSP_CAP_BATCH

>From the result , minimum and maximum time difference bewteen hw_ptr change
can varies from 20% to 400%