Hardware reset doesn't work

[mlac]

Hi there,

I have a custom board featuring the nRF52840. This is the relevant part of the schematic.

When pressing SW1, the SoC doesn't get reset. Seemingly, it's as if I hadn't pushed the button. Why is that?

Thanks in advance!

- Laci

[Simonr]

Hi

What have you programmed your custom board with here? Your .dts or .overlay file will need to have the following set in your board file to set the GPIO as a reset pin, so that could be one explanation as to why it's not doing anything: 

&uicr {
    gpio-as-nreset;
};

You can use the <YOUR_NCS_FOLDER>\zephyr\boards\arm\nrf52840dk_nrf52840\nrf52840dk_nrf52840.dts as reference here.

Best regards,

Simon

[mlac]

Hi Simon,

The behavior of RESET is independent of the provided device tree block. Is it possible that gpio-as-nreset is enabled by default?

Luckily, I think I have found the cause. Hardware resets are always reliable after replacing the 10K resistor on the RESET line with a 0-ohm resistor.

For comparison, this is the schematic of the nRF52840 USB dongle:

nRF528-DK schematic:

I don't know what made me add a 10K resistor, but I think it was unjustified. Do you agree that this is the cause of the issue?

Should I add a capacitor according to the dongle schematic? My product seems to be reliable without it.

[Simonr]

Hi

Okay, glad to hear you were able to figure it out. Most likely you thought it's better to have a pull-up too many than too few and added it. I agree that it is not necessary and that your solution should work just fine. For our board files in the device tree, the gpio-as-nreset is indeed enabled by default. I was just thinking if you had made a board file or overlay on your own that this might have been missing.

Let me know if this case can be closed then, or if you have any follow-up questions.

Best regards,

Simon