On Thu, 29 Jan 2009 09:11:40 +0100 Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > 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. > Is there a chance that the following might happen: - stop trigger, - hw_free - hw_params - prepare - start trigger I.e. without calling close and open? > 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(). > Yes, this is what I do today. I am considering if I should release the DMA stuff in hw_free and then in the prepare callback check if it needs to be prepared again (since it was released in hw_free). > 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. > Yes, I setup the cyclic DMA buffer the first time I get a prepare callback, and free the cyclic DMA buffer in the hw_free callback. This works fine as it is now, but I just want to make sure I handle all cases which might appear on the way. -- Best regards, Hans-Christian Egtvedt _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
