MMWAVEICBOOST: SPI Lines to connect to slave device

Hi, 

We have an IWR6843ISK and MMWAVEICBOOST which we are using for some evaluation purposes and software development. We want to connect this to a slave device using the SPI lines (MISO,MOSI,SPI_CLK,SPI_CS). 

I had an idea that it would be possible to bring these lines out through the two 20 pin connectors on the back of the MMWAVEICBOOST, however when using an oscilloscope I see that there is nothing on these lines. I then changed the 2:1 mux settings on S1 to the 40 pin BP/LP option (from the default) , which then showed some voltages on the connector pins. 

However, when I checked SPI_CLK on connector J5 pin 13, the signal was flat - in my mind this signal should be a clock pulse, or am I making a wrong assumption? Do I need to enable the SPI_CLK in software for the clock to show up? 

Is this the best way to bring out the SPI signals of the MMWAVEICBOOST to connect to an external device? Is there an alternative option for bringing out the SPI lines - e.g. the CAN interfaces? 

Many thanks, 

Peter