On 23.08.2013 22:13, Adam Reynolds wrote:
Does the CMX981 pulse its output CLK and FS during the receive cycle, or does it only pulse them during transmit and then silently wait for a reply?  From your message it sounds like it's always running the clock, but only pulses the FS on transmit and it's up to the Overo to pulse its own FS when it replies.

You might be able to use a GPIO to act as an FS, however I don't know if you'd be able to do it within that 10-12 clock cycle window.  What speed is the CMX981's clock running?

This page has some info about controlling a GPIO from the kernel:

Thanks for the link Adam. The serial clock (SCLK) of the CMX981 is always running and can be set to 2.2815, 4.563 or 9.126 MHz. And you are completely right, the CMX981 only sends data and the according framesync. The Overo has to generate a the active-high FS (1 SCLK cycle) and then send the data.

Best regards,