Unable to Program/Control NRF52840

Question

Hello,

I am running a simple experiment to turn on all GPIO pins to active on the NRF52840.

The code attached works on the NRF52840-DK, and I am able to measure 3v on the GPIO pins (e.g. pin P0.02).

However, when I program an external NRF52840 board, all the GPIO pins read 0.0V. I am able to see the board in NRF connect and get successful programming messages in the termnial. Am I missing something? Is there a difference in how to call the GPIO pins on the dev kit vs. a standalone board?

I am using:
- DK to program the board (by connecting VDD, GND, SWDIO and SWDCLK between the two boards, as well as SWDSEL to VDD on the DK)

- The defult board NRF52840DK_NRF52840 in the build configuration

- SDK 2.7.0-rc1 and Toolchain v2.6.1

- Traces connecting GPIO pins to a pad and measuring voltage between GND and the PAD. Is my hardware setup too naive? Do I need to add something else to make this simple setup work?

I'm a mechanical engineer by trade and doing my best to learn some electronics. So any help is greatly appreciated!

#include <zephyr/kernel.h>
#include <zephyr/device.h>
#include <zephyr/drivers/gpio.h>
#include <zephyr/sys/printk.h>

#define SLEEP_TIME_MS 500

void main(void)
{
    const struct device *gpio_dev = DEVICE_DT_GET(DT_NODELABEL(gpio0));
    int ret;
    uint32_t pin;

    if (gpio_dev == NULL) {
        printk("Error: Failed to bind to GPIO0\n");
        return;
    }

    for (pin = 0; pin < 32; pin++) {
        ret = gpio_pin_configure(gpio_dev, pin, GPIO_OUTPUT_ACTIVE);
        if (ret < 0) {
            printk("Error configuring pin %d\n", pin);
        }
    }

    while (1) {
        k_msleep(SLEEP_TIME_MS);
    }
}