Paul Kavan wrote:

I am wondering what piece of code contains the capture functionality for the at91 soc. I am hoping to see how and when the pcm activates the ssc at read time. I just cannot figure out why TD0 would behave at such with this set of code and yet behave correctly with my polling code. Not a criticism....just wanting to figure this out.

There is very little distinction between Playback and Capture in the ASoC AT91 implementation. Each SSC has 2 DMA structures, one for each direction. The Playback DMA structure points at the SSC PDC transmit registers and SSC transmit register masks, and the Capture DMA structure points at the SSC PDC receive registers and SSC receive masks. The DMA structure to use is selected in at91_ssc_hw_params().

By doing this, at91-pcm.c DMA code can simply run the DMA transfers without having to know which direction the data is being transferred.

Both receive and transmit SSC registers are initialized in at91_ssc_hw_params(), regardless of the direction.

../fam