On Thu, 29 Jan 2009 09:58:10 +0100 Clemens Ladisch clemens@ladisch.de 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@ladisch.de 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.