TK1 as I2S Slave

Hi
I want to replace the codec on the TK1 with my own expansion board.
I got the playback working but now I want to switch to capturing. To do that the Jetson TK1 has to be the slave. If I set to slave (in the audio device board-ardberg.c) and start to record I get an error after ~10 seconds “pcm_read:2031: read error: Input/Output error”.
The recorded file is empty (44 bytes).
I have the CLK and the SYNC and Data connected and I can see on the scope that they meet the requirements in the datasheet.

Is there a possibility to get more information on this error?
Do I have to set the platform driver to the external clock or does it do it automatically when i set to slave?