Hi,
I am testing a codec driver interfaced to the Raspberry Pi in TDM mode and on the logic analyzer I see that the I2S controller is shifting out data in slots 2 - 7 when playing 2 channel audio. The codec is master and only works at 256 x fs, so after the frame sync slots 0 and 1 transfer as they should but after that data continues to be shifted out. It is my understanding that the remaining bits should be zero padded.
On a similar note I see that the I2S bcm2835-i2s driver only supports 2 slots, but it seems it can also do 8. For example if I take an 8 channel audio source file(NOTE: I had to hack the file to look like 2 channels so hw_params didn't return an error) and play it I hear the first two channels fine and in the part that I am writing the dirver for I can easily route the other slots to additional DACs and get those to play as well.
So I guess I am wondering about two things:
1. In the first case why does my 2 channel audio get shifted out on all 8 slots? It seems if configured for 2 it should only shift data in the first two and wait for the next fsync before starting to shift again.
2. Why does the driver obly support 2 channels when it seems the hardware is capable of more?
I figure there is something about this controller that made this tricky or impossible, but I am still curious about it.
Regards,
Steven