On Thu, 29 Jan 2009 10:59:51 +0100 Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > Hans-Christian Egtvedt wrote: > > 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 would work, but doing it in the hw_params callback would be a > little more simple: > * In hw_params, free the old buffer (if it exists), then setup the > buffer; I think I was not 100% clear, in addition to call snd_pcm_lib_malloc_pages() in hw_params, I also need to hand over the DMA buffer information to a prepare function in the DMA driver I use with this sound hardware. So I follow the scheme for free/setup of buffers for my DMA controller setup as well. hw_params, release DMA controller if exists, then prepare DMA controller. > * in hw_free, free the buffer. > Which I do by calling snd_pcm_lib_free_pages(). and then in hw_free, release DMA controller if exists. > As a rule of thumb, the callbacks open/close, hw_params/hw_free and > start/stop trigger are mostly symmetrical, and any resources should be > allocated and freed in the functions that belong together. (The start > trigger is a special case because it uses two callbacks, prepare and > trigger with TRIGGER_START.) > > The hw_params and prepare callbacks can be called multiple times. > Noted, which means I should reprepare my DMA controller as well every time I get a hw_params callback and do snd_pcm_lib_malloc_pages(). > > Is there a flow chart which shows how the different callbacks can be > > called? > > Not yet. > Would probably help me a lot to see the actual flow of the callbacks. -- Best regards, Hans-Christian Egtvedt _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
