Hi Clemens, That is where my confusion was. When you said hw_params are only what the HW supports (makes sense :) ). Making minchan=maxchan, I can now record less than max channels. Thanks for the help! On Wed, Sep 21, 2016 at 12:01 AM, Clemens Ladisch <clemens@xxxxxxxxxx> wrote: > Rob Nertney wrote: > > I'm building the hardware, so I can technically do whatever I want. I > > didn't want to add more to the hardware if ALSA can handle this. > > > > The hardware is spec-ed to *always* have 16 channels worth of data being > > written into DDR. I think this comes full-circle to my original question > of > > whether arecord can filter out channels. > > When the ALSA library automatically converts sample formats, it can also > adjust the number of channels. (This does not happen if some program > decides to use the "hw" device to bypass all conversions.) > > > It sounds like arecord can handle multiple channels, but its under the > > assumption that the hardware itself changes (in the pcm_open function) to > > only copy in the requested channels worth of data; i.e. arecord assumes > > that the data in dma_area is exactly as requested by arecord. > > The ALSA kernel framework assumes that the snd_pcm_hw constraints correctly > describe the capabilities of your hardware. Any conversions happen in > userspace. > > Your driver never sees what happens in userspace; the values to be set by > the .hw_params callback are guaranteed to fit into your driver's > constraints. > > > Regards, > Clemens > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
