From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clemens Ladisch Subject: Re: Can DMA address, periods, buffer size, etc change after hw_params is called? Date: Thu, 29 Jan 2009 09:11:40 +0100 Message-ID: <498164BC.6080907@ladisch.de> References: <20090129081825.241be9e4@hcegtvedt> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from out5.smtp.messagingengine.com (out5.smtp.messagingengine.com [66.111.4.29]) by alsa0.perex.cz (Postfix) with ESMTP id 34031103849 for ; Thu, 29 Jan 2009 09:11:45 +0100 (CET) In-Reply-To: <20090129081825.241be9e4@hcegtvedt> 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: Hans-Christian Egtvedt Cc: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org Hans-Christian Egtvedt wrote: > I wonder if I must take care handling changes in DMA address, number of > periods and period size in the prepare callback? > > Or are these locked after the first time prepare is called? The hardware parameters like buffer/period size and sample format are set by calling the hw_params callback; they are valid until a call to hw_free (or another call to hw_params), which doesn't happen while the stream is running. The DMA address is selected by the driver in the hw_params callback, but most drivers let the framework handle this by calling snd_pcm_lib_malloc_pages(). The prepare and start/stop trigger callbacks are called only between hw_params/hw_free, but they could be called multiple times, so you should handle this stuff in the prepare callback only if your device requires that this is done every time before a stream is started. Best regards, Clemens