On Thu, 26 Feb 2004, Gupta, Kshitij wrote:
> hi ,
> That's correct the pages will be in whole meory space and I will be
> using snd_pcm_lib_preallocate_pages_for_all api for allocating the space.
> There are some DMA apis (for our dma framework) like
>
> set_dma_transfer_params(srcaddr, destaddr, mode ...)
>
> Now I need to call this API whenever the transmit for one of the buffers is
> complete. Or is it like, these things should be done just once upfront.
> But that means we need n channels if we want n buffers to be ring buffers.
The ALSA midlevel expects if trigger callback is called, then the data
starts the transfer from the allocated ring buffer (which is filled by the
ALSA midlevel code or application - mmap mode). It's not necessary that
ring buffer is continous from the physical memory perspective, but it must
be continuous from the user space perspective (using MMU and page
mapping).
Then after one period transfer is finished, you need to call
period_elapsed() callback from the interrupt to notify ALSA midlevel code
about this situation and continue with the DMA transfer (next period).
Note that the pointer callback must give the actual pointer in the ring
buffer at this point.
I hope this helps.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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