Real time control loop with softdevice S140 and nrf52840.

RE: Real time control loop with softdevice S140 and nrf52840.

Sietse — Sun, 29 Nov 2020 09:49:37 GMT

Upon closer examination there were a few deviations from 328 that more or less corresponding to the BLE communication, but not more than 3, so about 0.1ms. I now assume that is perfectly possible to get a control loop of up to 1000Hz under these circumstances.

RE: Real time control loop with softdevice S140 and nrf52840.

Sietse — Sat, 28 Nov 2020 22:00:01 GMT

Thanks for the response.

I added a timer to the app using app_timer_create and made it run each 10ms.

I logged NRF_RTC0->COUNTER in an array for 20 seconds and printed it afterwards.

The counter values change 328 each and every time, even when I send some data over BLE. I couldn't measure any jitter with this timer, or at least less than 0.1ms. It seems to work perfectly, although I still can't believe that it works this perfectly. So it seems entirely feasible.

RE: Real time control loop with softdevice S140 and nrf52840.

run_ar — Fri, 27 Nov 2020 10:17:51 GMT

Hi,

Details on the SD Interrupt model and processor availability.

If you run the SD and the pid needs the cpu you will have conflicts if they are both active at the same time. I.e. in case the SD is advertising, scanning or in a connection.

If you are not running the PID while the SD is active, you should not see any issues as you say. Just remember to run your motor control at highest priority.

If you want the PID to have priority over the SD this is also possible by redefining the interrupt priorities. However this could lead to timing issues in the SD and possibly make it assert.