Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

MatryoshkaLJY — Tue, 25 Mar 2025 11:58:27 GMT

The probe is calibrated, I'll try to find a higher impedance probe.

Thanks for your help, my development can be continued.

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

Einar Thorsrud — Tue, 25 Mar 2025 11:22:22 GMT

That is interesting, I wonder if the probe is a problem in itself here. And the measuremnts look odd. Do you have a higher impedance probe you can use? And is the probe properly calibrated with the oscillioscope?

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

MatryoshkaLJY — Tue, 25 Mar 2025 10:01:58 GMT

Sure. I measured the clock signal with sensor disconnected.

And the waveform looks like this.

Attaching the probe to the clk pin leads to communication failure when the sensor is connected to the DK.

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

Einar Thorsrud — Tue, 25 Mar 2025 08:49:47 GMT

I see. Could there be a lot of capacitance on the sensor board for some reason? Seem unlikely, but it would be interesting if you could measure the clock signal directly on the DK, with the sensor disconected. Does the clock signal look better then?

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

MatryoshkaLJY — Mon, 24 Mar 2025 13:24:41 GMT

Thanks for your reply. I double-checked the PIN_CNF register and the drive strength is H0H1. I shortened the signal path, mounted the sensor pcb directly to the DK. Following is my current setup, the sensor is on the green PCB.

Now when I set the drive strength H0H1, spi frequency 4MHz, it works, but fails when I set higher frequency or weaker drive strength.

RE: Weak Pin Drive Strength on nRF5340 DK Leading to SPI Communication Failure with ICM-42688-P

Einar Thorsrud — Fri, 21 Mar 2025 08:57:31 GMT

Hi,

[quote user=""]Are there additional configurations (e.g., slew rate, pin control settings) to further optimize the GPIO output characteristics on the nRF5340?[/quote]

The pins are configured as high drive for both low and high state, and there is nothing more you can do in that regard. However, you could double-check the PIN_CNF register for the clock pin with a debugger to verify that it really has high drive enabled?

[quote user=""]Could this be related to hardware design limitations (e.g., pull-up/down resistors, trace impedance) on the nRF5340 DK?[/quote]

Yes. Though these pins are not used for anythign specical, so I wonder if it could be related to other/external parts of the cuircuitry, for instance if you have very long wires? Or are there other things that could introduce higher capacitance on thei SPI lines? Can you share a photo of your setup?

[quote user=""]Are there known workarounds or firmware adjustments to mitigate this issue?[/quote]

Not other than ensuring you have high drive. In addition to checking the register, you can also see where it is confiugred in the nrfx driver, nrfx_spim.c.