On Thu, 29 Jan 2009 09:58:10 +0100 Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > Hans-Christian Egtvedt wrote: > > 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? > > Yes. > > It is also possible that the same happens without hw_free, i.e., > hw_params has to initialize _or_ to change the parameters. > Okay, so to be sure I setup and release my cyclic DMA buffer safely I could use the following model: in prepare callback setup the DMA buffer, once when called. The hardware parameters should not change at this point. If I get a hw_params callback after a prepare, then release the DMA buffer, and set it up again in the prepare callback? Final cleanup of the DMA buffer can/should be done in hw_free? This sounds safe given my understanding of ALSA. Is there a flow chart which shows how the different callbacks can be called? > > Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > > > 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 framework guarantees that prepare is called only when the hardware > parameters are set. > Noted. -- Best regards, Hans-Christian Egtvedt _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
