RE: Is there any spis event generated when the slave is selected?

Jørn — Fri, 18 Aug 2017 09:03:08 GMT

Hello User1321

I might have misinterpreted your question a bit, but I believe at least parts of my answer might still give you what you need.

I have used a GPIOTE event on the CS pin, PPI and the Capture task of a timer. I have attached a project, it is based on the SPIS example in SDK 14. I have added timer and PPI defines to sdk_config as well as the necessary .h and .c files. Please note that it is not optimized in any way.

For my test I used a nRF52832 DK as slave and nRF52840 DK as master. The CS pin generates a GPIOTE event on toggle which triggers the capture task with the timer. The capture values are stored in seperate variables in the CS GPIOTE interrupt, in the gp_evt_handler.

The slave transmits the difference between timer values back to the master, which displays it in the log in putty.

The difference value you get is dependent on SPI bit-rate and timer clock rate. In the example the timer is set to 4MHz. The difference variable is a 16 bit value which is transmitted Least significant byte first. The actual time spent with CS low is found by dividing the difference value on the timer clock frequency.

There is a delay from the time the CS pin falls, until the GPIOTE event handler executes which is roughly 24 us.

DO NOTE: The timer is simply running free in this example, it is never stopped or cleared in a controlled fashion. If the timer overflows and restarts from zero between CS falling edge and CS rising edge you will get an erronous value.

Best regards

Jørn Frøysa

spis - w timer.zip

RE: Is there any spis event generated when the slave is selected?

User1321 — Thu, 17 Aug 2017 09:31:57 GMT

Yes, I tried putting the same spis_slave select pin on the GPIOTE interrupt configuration but on the initialization it gets restarted. When I change the interrupt pin to a different one, the GPIOTE interrupt works fine. I guess the same pin cannot be used to spi_slave select and also an GPIOTE interrupt.

RE: Is there any spis event generated when the slave is selected?

endnode — Thu, 17 Aug 2017 09:21:54 GMT

You mean that nRF52 is SPI slave, right? Have you tried GPIOTE interrupt on that PIN?