NRF9160 SPI: Spikes on MISO and CS lines

[Nils Ruf]

Hello,

we are connecting an NRF9160 with a WFM200 wifi chip over SPI using Zephyr RTOS. Additionally, we manually control the chip select pin in the driver code for the wifi module.

During the communication we are frequently receiving spikes on the CS and MISO lines as shown in the image below:

We already checked the driver for race conditions, etc., however, the control logic for the chip select pin looks fine.
The communication generally works but the spikes (at least from CS) seem to cause packet receive errors on both sides leading to a decreased performance.

Do you know what could be the cause of this?
Thank you very much in advance.

Kind regards

Nils

[Kenneth]

Looks like some noise on the MISO line, this pin is driven by the peer (wifi chip). I suspect there is some volage/current "bounce back", in lack of a better word, due to inductance or capacitance in wires or similiar, I suggest to improve grounding between the boards, and also place the SPI wires and ground wire(s) close together, possible shorten them also. This is an electrical hardware problem, not related to software.

Best regards,
Kenneth

[Nils Ruf]

Thanks for the quick reply. I will look into this...