Sergei Steshenko wrote: > Tomas Carnecky <[EMAIL PROTECTED]> wrote: > > Clemens Ladisch wrote: > > > Your application must be able to handle any period size. > > > > > > Why does the period size matter at all? > > > > My app can handle that now, but the way how I had to do it defeats the > > 'zero-copy' paradigm. > > > > The situation is this: the application requests a 16kb buffer, at 2 > > channels / U16LE this makes a 4096 frames. It's a streaming buffer and > > the app writes in the data in chunks of 4096 bytes. I can't map the alsa > > mmap'ed buffer to the application (because of the different size) so I > > have to create my own temporary buffer and then copy the data to the > > mmap'ed buffer. > > I might be wrong, but it seems that 4096 bytes limit comes from these > facts: > > 1) on Linux page size is 4096 bytes;
(depends on the architecture) > 2) if one allocate more than 4096 bytes, the system cannot guarantee the > pages are contiguous; One can try, but the system doesn't guarantee that it succeeds. > 3) ALSA uses DMA whenever the card supports it; Almost all cards actually _require_ DMA. > 4) DMA needs contiguous buffer, so we are back to one page 4096 bytes > buffer. ALSA's buffer is continuous (when needed). If ALSA isn't able to allocate it, setting the hardware parameters fails. HTH Clemens ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Alsa-user mailing list Alsa-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/alsa-user
