From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefano Panella Subject: Re: paravirtualized alsa kernel driver for XEN Date: Wed, 21 Mar 2012 10:16:43 +0000 Message-ID: <4F69AA8B.3080409@citrix.com> References: <4F6769A9.6090200@citrix.com> <4F6881B6.2020903@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from SMTP.EU.CITRIX.COM (smtp.ctxuk.citrix.com [62.200.22.115]) by alsa0.perex.cz (Postfix) with ESMTP id 4CE292439A for ; Wed, 21 Mar 2012 11:07:21 +0100 (CET) In-Reply-To: <4F6881B6.2020903@ladisch.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: Clemens Ladisch Cc: "alsa-devel@alsa-project.org" List-Id: alsa-devel@alsa-project.org Hi, Thanks for taking the time to answer about this detail. On 20/03/12 13:10, Clemens Ladisch wrote: > Stefano Panella wrote: >> I have been reading the documentation on "Writing an ALSA Driver" and I >> am still not completely clear on the meaning of the "pointer" callback >> in the pcm operations. >> >> 1) In case of a playback stream, is the pointer referring to wich sample >> is currently playing on the DAC or to which is it the last frame read by >> the HW from the alsa memory buffer? > > It's the position of the first frame not yet read from the memory buffer. > > The delay between the DMA and the DAC output would be reported by > adjusting runtime->delay, but drivers usually do not bother to do this, > except when this delay becomes rather large because of additional > queueing, e.g., in the USB driver. > ok, I was wondering about applications like skype, trying to do some background noise cancellation, or to eliminate echo when using speakers. I was thinking in this case the delay should be accurate for Playback and Capture as well, or am I wrong? >> 4) is there any test I could run to check I have implemented correctly >> the "pointer" callback? Or any application which would need very high >> "pointer" precision like frame precision? > > PulseAudio. > Or run mplayer and look at the A-V value in the status line. > I will try these as well. > > Regards, > Clemens In case this pv XEN alsa driver will start to work properly, where should I post the patches? Who is currently the linux kernel alsa driver mantainer? Thanks again, Stefano.