GPIO state not retained after FOTA reboot on nRF54L15 (Zephyr SDK 3.0.2)

[Jishnu K J]

Hi,

I am using nRF54L15 with Zephyr RTOS in nRF Connect SDK v3.0.2.

After performing a FOTA update, the device reboots. I need to retain the state of a GPIO pin across this reboot.

The GPIO I am trying to retain is P1.06. I attempted to configure it with retention using the following code:

#define PIN_P1_06 38
#define P1_INDEX  6

void configure_retained_gpio(void) {
    // Configure the pin as output with retention enabled
    nrf_gpio_cfg_output(PIN_P1_06);
 
    NRF_P1->PIN_CNF[P1_INDEX] &= ~GPIO_PIN_CNF_CTRLSEL_Msk;
    NRF_P1->PIN_CNF[P1_INDEX] |= (GPIO_PIN_CNF_CTRLSEL_GPIO << GPIO_PIN_CNF_CTRLSEL_Pos);
}

However, after the OTA update and subsequent reboot, the GPIO state is cleared and does not retain the previous value.

My questions:

1. Is there any additional configuration required in nRF54L15 to retain GPIO states across a reboot after FOTA?

2. Is GPIO retention supported across MCU reset triggered by FOTA, or is it only supported for specific low-power modes?

Any guidance or recommended approach to preserve the GPIO state across OTA reboot would be greatly appreciated.

Thanks.

[Menon]

Hello,

In this case, I don’t think GPIO retention is the right approach.

Instead, it’s worth trying to initialize the pin as early as possible in the bootloader. I’m not 100% sure this will work though, since it depends on how the GPIO behaves during reset. If the pin goes high-Z, it won’t actively drive the line low, so it may stay on long enough for the bootloader to re-assert it.

Kind Regards,

Abhijith

[Jishnu K J]

Hello Abhijith,

I tried configuring the GPIO pin in the bootloader, but it did not work. I suspect that the overlay file I created (mcuboot.overlay) is not being applied during the boot process.

The overlay file I used is shown below:

&gpio1 {
    status = "okay";

    /* Ensure P1.06 stays HIGH during MCUboot */
    load_cell_en_hog: load-cell-en-hog {
        gpio-hog;
        gpios = <&gpio1 6 GPIO_ACTIVE_HIGH>;
        output-high;
        line-name = "load-cell-enable";
    };
};

The file is placed at:

my_project/
 └── child_image/
      └── mcuboot.overlay

I have also added CONFIG_BOOTLOADER_MCUBOOT=y in sysbuild.conf.

Is there anything I might be missing? Also, is there any documentation available for properly applying overlays to MCUboot?

Best regards,

Jishnu K J