Issues with nRFX SAADC Driver when sampling through DPPI

RE: Issues with nRFX SAADC Driver when sampling through DPPI

hotbeefcurry — Mon, 18 Mar 2024 17:16:58 GMT

Thanks.

We are going to pursue other methods.

RE: Issues with nRFX SAADC Driver when sampling through DPPI

Kenneth — Mon, 18 Mar 2024 10:19:02 GMT

[quote user="hotbeefcurry"]This behavior is possible on the 5340 as I have it working, but I cannot get it working with the stock driver. Can you take a look at the SAADC driver file and let me know if this is even possible to do with the stock driver? [/quote]

In general I can say that it's very little support for setting up ppi in zephyr, so I am not surprised if the "stock driver" does not support this out of the box. The suggested code by Jared should add extra current to call the the nrfx_saadc_mode_trigger() as you write, but other than that it should consume the normal 2-4 uA idle current between sampling when using k_timer()/k_sleep().

Kenneth

RE: Issues with nRFX SAADC Driver when sampling through DPPI

hotbeefcurry — Fri, 15 Mar 2024 20:11:44 GMT

Hi Kenneth,

Thanks for the reply & thanks for the note about not needing to call stop.

I checked out the example you linked. Unfortunately, they use a software timer to trigger a handler that calls nrfx_saadc_mode_trigger(void). I have tested something similar to this in the past and it consumes significantly more power. I understand I could simply use an RTC interrupt & callback to call nrfx_saadc_mode_trigger(void), however this also consumes more power due to the CPU running the handler.

I am hoping to start & sample the SAADC peripheral using the RTC & DPPI without CPU intervention until the SAADC sends the end event and triggers the interrupt.

This behavior is possible on the 5340 as I have it working, but I cannot get it working with the stock driver. Can you take a look at the SAADC driver file and let me know if this is even possible to do with the stock driver?

RE: Issues with nRFX SAADC Driver when sampling through DPPI

Kenneth — Thu, 14 Mar 2024 22:02:38 GMT

Hello,

Even thought I would love to try this myself, I unfortunately don't have time.

Instead, and with the polling rate you are describing, I would have looked at the example Jared made here:
RE: nrf5340: cpunet accessing SAADC

Maybe it's even possible to develop on that example, such that instead of calling nrfx_saadc_mode_trigger(), that you trigger it from a ppi channel. As you can see from the sample code, you don't need to start or stop to achieve low power.

Kenneth