On Fri, 02 Mar 2007 22:57:39 +0100 Matthias Nyffenegger <matthias.nyffenegger@xxxxxxxxxx> wrote: > Hi, > > I am trying to write an alsa driver for my audiowerk8 soundcard. > The aw8 uses a Philips saa7146 chipset. There are 2 capture and > 8 playback channels mapped on the saa7146's DMA as follows: > > DMA1: 2xcapture > DMA2: 4xplayback > DMA3: 4xplayback > > Sample format is 16bit. > > Frame format is as follows: > (A number corresponds to a channel, a stereo channel-pair is embraced > by [] and 1 digit corresponds to one sample byte) > > capture channels [0,1] on DMA1: 00--11-- > playback channels [2,3],[4,5] on DMA2: 22443355 > playback channels [6,7],[8,9] on DMA3: 66887799 > > I guess this is interleaved format. Not exactly. The interleaved format used by ALSA and most hardware is that the data of each audio frame is written requentially [0,1,2,3,...]. In you case the data is interleaved, but the channel order is different [0,2,1,3]. It means that if you try to play a stereo sound through DMA2 the sound is sent to the left channels of the two stereo pairs. You can solve this problem later. > Since I don't really understand the relation between DMA, substreams, > frames and channels I wonder how a alsa substreams map best to this > configuration: DMA channels depend on the hardware. A substream is a logical thing. You have to decide their relation. > 1) 1 substream per DMA The simplest way. The downside is that who opens the device monopolyzes all 4 channels regardless how may it really uses. > -> can alsa handle frames with more than 2 channels, and if yes, how? You have to set it, just like any other parameter, constraint, capability: substream->runtime->hw.channels_max = n; > 2) 1 substream per stereo channel-pair It's possible only if a DMA channel can handle two independent substreams. For example, can only one of the spereo pair play something (while the other is stopped/paused) ? Other hw limitations may apply (eg. the sample rate and the playback volume may be the same for all 4 channels). > 3) 1 substream per channel Same as above. -- Giuliano. ------------------------------------------------------------------------- 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-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
