How to tell when a SPIS transaction is granted

[jtrovato]

I am trying to implement a REQ line protocol over GPIO to signal to the Master when it is ok to receive data. Basically, I want to pull the REQ line high when the nrf51 has something to send to the master, I then want to pull the REQ low as soon as the SPIS transaction is started so as soon as the CSN line goes low (so I know that the Master is receiving the data). From what I can discern, this is once the CSN line goes low AND the SPIS module has acquired the semaphore. Is there any interrupt or event I can use to toggle the REQ line at this point?

[Stefan Birnir Sverrisson]

Hi

I suspect you could set up GPIOTE channel with the CSN pin and connect it to another GPIOTE channel that is set up with the REQ pin. Connect the GPIOTE channels with PPI. An example how to connect GPIOTE with PPI is in the gpiote example in the SDK.