SPIM4 Configuration Issues with NRF5340dk board

RE: SPIM4 Configuration Issues with NRF5340dk board

Turbo J — Fri, 23 Jan 2026 06:22:19 GMT

Check hardware docs or the DK backside - P0.10 is CTS from the debug interface MCU.

You have 2 outputs fighting each other.

RE: SPIM4 Configuration Issues with NRF5340dk board

vibai — Fri, 23 Jan 2026 02:58:16 GMT

Hi Vidar,

I hope you’re doing well. I had to pause this development effort for a bit, but I’ve recently picked it back up.

While running the exact script you shared on my nRF5340DK board, I noticed something unexpected: pin P0.10 only reaches about 1.5 V, whereas the other pins (P0.09, P0.08, and P0.11) reach the expected 3 V. I also cut the solder bridge (SB50) associated with P0.10 based on your suggestion due to the automatic HWFC detection issues, but that didn’t seem to improve the behavior.

This issue appears to be unique to P0.10. When I moved the same logic to a different pin, it reached 3V as expected. I also don’t believe this is a bus conflict, since the code you shared explicitly disables any other buses P0.10. I’ve observed the same behavior on a second board as well, which makes me suspect there may be a configuration detail I’m missing or something fundamentally different about this pin that I’m not accounting for.

Do you have any ideas on what might be causing this? I’ve attached a logic analyzer capture for reference. Thank you!

RE: SPIM4 Configuration Issues with NRF5340dk board

Vidar Berg — Mon, 01 Sep 2025 06:37:33 GMT

I'm glad to hear that you found the problem.

[quote user="vibai"]One thing I did notice: on a board where I had cut the solder bridge for the RTS signal, P0.10 measured at a little under half of the expected voltage (~1.3 V) compared to the ~3.0 V seen on the other pins. When I swapped to a new board (with the solder bridges intact), the problem went away. Out of curiosity, do you happen to have any idea what could be causing that behavior?[/quote]

I'm not sure what the reason for this could be, unfortunately. It depends on what the pin state was when you measured the voltage. If it was configured as an output and kept high (no toggling), then it could potentially be a hardware issue, such as a blown ESD diode. But this seems less likely.

RE: SPIM4 Configuration Issues with NRF5340dk board

vibai — Fri, 29 Aug 2025 22:45:57 GMT

Hi Vidar,

Thanks for running that test and sharing the details. After double-checking, I realized the issue was on my end, I was using the wrong pinout. With the corrected assignments, I was able to reproduce the same behavior you showed using your test code.

One thing I did notice: on a board where I had cut the solder bridge for the RTS signal, P0.10 measured at a little under half of the expected voltage (~1.3 V) compared to the ~3.0 V seen on the other pins. When I swapped to a new board (with the solder bridges intact), the problem went away. Out of curiosity, do you happen to have any idea what could be causing that behavior?

Thanks again for your help! It is very much appreciated!

RE: SPIM4 Configuration Issues with NRF5340dk board

Vidar Berg — Fri, 29 Aug 2025 08:48:26 GMT

Hi,

The physical connections shown in the linked picture do not match your pin assignments. Perhaps you uploaded the wrong picture? In any case, I made a simple test to check if the pins are available on the DK.

Log trace from my test

Test project

devzone.nordicsemi.com/.../3731.gpio_5F00_test.zip

NOTE: Not shown here, but P0.10/RTS was sometimes pulled low by the interface MCU because of automatic HWFC detection failing. As mentioned in the user guide, the UART lines are supposed to be tri-stated when no terminal is connected. To make this more reliable you may need to cut the solder bridge for the RTS signal (https://docs.nordicsemi.com/bundle/ug_nrf5340_dk/page/UG/dk/solder_bridge.html)

RE: SPIM4 Configuration Issues with NRF5340dk board

vibai — Thu, 28 Aug 2025 18:10:36 GMT

Hi Vidar,

I’m still seeing the same results after disabling buttons 2 and 3 in the overlay. Based on Turbo J advice, I took a closer look at the generated DTS and noticed that the gpio_fwd node is using pins P0.10 and P0.11 as forwarding pins, which are also used by uart1. So in addition with those buttons, the gpio_fwd nodes, and uart1 node I made sure to set them to disabled, and verified that it was reflected In the final device tree. However, I am still observing the same behavior where nothing shows up on the logic analyzer.

My new overlay file:

/ {
	aliases {
		spi-loopback = &spi4;
	};
};
&pinctrl {
    spi4_default: spi4_default { 
        group1 {
            psels = <NRF_PSEL(SPIM_SCK, 0, 8)>,   
                    <NRF_PSEL(SPIM_MOSI, 0, 10)>,  
                    <NRF_PSEL(SPIM_MISO, 0, 9)>;  

        };
    };

    spi4_sleep: spi4_sleep {
         group1 {
            psels = <NRF_PSEL(SPIM_SCK, 0, 8)>,   
                    <NRF_PSEL(SPIM_MOSI, 0, 10)>,  
                    <NRF_PSEL(SPIM_MISO, 0, 9)>;  
            low-power-enable; 
        };
    };
};

&spi4 {
	compatible = "nordic,nrf-spim";
	status = "okay";
	pinctrl-0 = <&spi4_default>;
	pinctrl-1 = <&spi4_sleep>;
	pinctrl-names = "default", "sleep";
	cs-gpios = <&gpio0 11 GPIO_ACTIVE_LOW>;

};

&arduino_adc{
    status="disabled";
};
&led0 {
    status = "disabled";
};

&led1 {
    status = "disabled";
};

&led2 {
    status = "disabled";
};

&led3 {
    status = "disabled";
};
&qspi{
    status = "disabled";
};
&button2{
    status="disabled";
};
&button3{
    status="disabled";
};
&gpio_fwd{
    status="disabled";
};
&uart1 {
    status="disabled";
};

Heres a link to the screen shot of my physical pinout: drive.google.com/.../view

RE: SPIM4 Configuration Issues with NRF5340dk board

Vidar Berg — Thu, 28 Aug 2025 13:20:14 GMT

Hello,

From the silkscreen on the backside of the DK, you can see that P0.08–P0.09 are assigned to buttons 3 and 4, P0.10 to the UART RTS signal, and P0.11 to SWO (Virtual serial ports, Buttons and LEDs). Out of these, I think it's only the RTS signal that may be problematic since it's connected to the interface MCU. Do you see the same if you disable button 2 and 3 in your overlay?

&button2 {
    status = "disabled";
};
&button3 {
    status = "disabled";
};

Best regards,

Vidar

RE: SPIM4 Configuration Issues with NRF5340dk board

Turbo J — Thu, 28 Aug 2025 06:24:46 GMT

Look at the finished dts files in build/zephyr sub directories - a bunch of these pins are used elsewhere in the DK or may even be forwarded to the net core by default. The DTS parsers don't catch all possible mistakes.