RE: Continuous DAC sine generation using SPIM and a HW counter (combined via PPI)

Pjay — Wed, 06 Nov 2019 11:40:11 GMT

I found a solution: I have implemented a second hw timer/counter configured as counter similar as in the link above. With the main timer I transmit 2 bytes over SPI (triggered by the CC event via PPI). The counter is connected via PPI with the SPI transfer done address and counts each transfer done event. After N events (where N is configurable) the counter generates an interrupt, and in the interrupt handler I increment the pointer regarding my sine array (look-up table).
I don't know if this is the best solution as I still need to involve CPU for pointer incrementing, but it is better than per event scheduling (regarding timing robustness).
It was a little tricky with SPI because the CS pin is not toggled automatically by the driver. Here I adapted a solution mentioned here: https://devzone.nordicsemi.com/f/nordic-q-a/18645/no-slave-select-on-spim-xfer-using-ppi-and-gpiote