On Thu, 29 Jan 2009 10:59:51 +0100 Clemens Ladisch clemens@ladisch.de 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.