From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raymond Yau Subject: Re: PulseAudio and SNDRV_PCM_INFO_BATCH Date: Fri, 19 Jun 2015 09:17:08 +0800 Message-ID: References: <557E86DD.8020709@metafoo.de> <557EBEAA.70004@metafoo.de> <557EDE22.7080808@metafoo.de> <55812F5C.8010502@metafoo.de> <55818DB5.6050007@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-oi0-f45.google.com (mail-oi0-f45.google.com [209.85.218.45]) by alsa0.perex.cz (Postfix) with ESMTP id E3190260493 for ; Fri, 19 Jun 2015 03:17:09 +0200 (CEST) Received: by oigb199 with SMTP id b199so28440862oig.3 for ; Thu, 18 Jun 2015 18:17:08 -0700 (PDT) In-Reply-To: <55818DB5.6050007@canonical.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: David Henningsson Cc: Tanu Kaskinen , Lars-Peter Clausen , Takashi Iwai , clemens@ladisch.de, ALSA Development Mailing List , Arun Raghavan List-Id: alsa-devel@alsa-project.org > 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%