Hi, AFAIK, it seems that when using a scatter gather buffer, not every period is located inside of a page. If for example i use a period size of 3000 bytes and a Scatter Gather buffer, i would have this:
pages : page0, page1, page2 ... periods: p0, p1, p2, p3, p4 ... |...page0...||...page1...||...page3...| |...p0...||...p1...||...p2...||...p3...| The problem is that a DMA transfer can not go accross 2 different pages. On Aureal hardware, even on contiguous buffers this causes all sort of odd problems. Each DMA chunk must be on the same page. So i would have to do this: d0, d1, d2, d3 : DMA chunks programmed in hardware. There are 4 for each DMA channel. |...page0...||...page1...||...page3...| |...p0...||..|.p1...||...p2...||...p3...| |...d0...||d1||.d2..||d3||.d0.||..d1..| That means that i would have to split each period that crosses a page boundary into 2 DMA chunks, with all the complications involved because of irregular sizes, offsets... ARghhh! I could just leave the period size as a power of 2, on that way, a period would never cross any page boundary, but most ALSA programs are too picky to accept that kind of restrictions in most cases. ---------------------------------------------- Regarding the "Writing a ALSA driver" Docbook: Regarding the Non contiguous buffers, that the sgbuf struct can be derived as: snd_pcm_sgbuf_t *sgbuf = (snd_pcm_sgbuf_t*)substream->dma_private; But there is a problem: The substream->dma_private is only valid after snd_pcm_lib_malloc_pages() has been called. Maybe it would be nice to hint about this small detail in the document. Best Regards Manuel ------------------------------------------------------- SF.Net is sponsored by: Speed Start Your Linux Apps Now. Build and deploy apps & Web services for Linux with a free DVD software kit from IBM. Click Now! http://ads.osdn.com/?ad_id=1356&alloc_id=3438&op=click _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
