High frequency SAADC sample with Softdevice

[Jacques]

I'm using an NRF52840, SoftDevice s140, FreeRTOS, SDK 15.3.0.

I'm trying to sample my ADC at high speed, >1khz (10-40kHz).

I implemented the logic from the SAADC exaple, using PPI and nrf_drv_timer, and I managed to set the speed of the trigger timer in the range of microseconds.

But with the softdevice enabled, the timing is very inconsistent and inaccurate. I have read a few comments confirming this, but can't figure out what the alternative is.

What options are there for a high speed timer used in conjunction with the softdevice and freeRTOS?

[Kenneth]

I am not familiar with how you can do it with FreeRTOS, but the implementation in \saadc should be able to run without any issue using normal SDK + SD. You may however increase the NRFX_SAADC_CONFIG_IRQ_PRIORITY priority to to 3 (instead of 6). Just make sure that you don't call any softdevice calls from the saadc_callback() in this case, since it will not be able to do softdevice api calls from this interrupt level, ref:

https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/processor_avail_interrupt_latency/exception_mgmt_sd.html