DMA, substream, frame, channel - how is this all related

[Matthias Nyffenegger <matthias.nyffenegger@bluewin.ch>]

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.

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:
1) 1 substream per DMA
   -> can alsa handle frames with more than 2 channels, and if yes, how?
2) 1 substream per stereo channel-pair
3) 1 substream per channel


Regards, Matthias




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