nRF52840-DK only executing while debugging

RE: nRF52840-DK only executing while debugging

Thomas_1 — Tue, 16 Dec 2025 16:08:37 GMT

Thank you SO MUCH. I have struggled with this problem for hours and now it is finally working (You were right I did not disable the DCDC converter). I really can not thank you enough for your help. You saved my entire project!

Best regards

Thomas

RE: nRF52840-DK only executing while debugging

Vidar Berg — Mon, 15 Dec 2025 13:36:30 GMT

The DK build targets will also enable the DCDC regulator by default which will not work reliably if the DCDC inductors are not present on the board (are not included in the MDBT42V module). This is not a typical failure mode I have seen on the nRF52840 DK, but it may be worth trying to disable the DCDC by creating an DT overlay to change it back to LDO (Note: LDO mode is forced on in debug interface mode). You may also do a visual inspection of the board to make sure the indcutors or any other components around the 52840 target are not missing.

https://github.com/zephyrproject-rtos/zephyr/blob/44eaeb011944db7b919c581d6381230f8e6402e5/dts/arm/nordic/nrf52840.dtsi#L102

RE: nRF52840-DK only executing while debugging

timonsku — Sun, 14 Dec 2025 22:01:31 GMT

ok yea nvm the bootloader still worked, holding reset while powering on brought up the OB bootloader and reflashing it brought it back to life. The nRF52 itself still behaving weird as before but at least the board is alive

RE: nRF52840-DK only executing while debugging

timonsku — Sun, 14 Dec 2025 20:57:47 GMT

there is no USB device coming up, if its still alive that would probably have to be flashed via SWD?

RE: nRF52840-DK only executing while debugging

Turbo J — Sun, 14 Dec 2025 17:04:31 GMT

Likely only needs to apply "Interface MCU firmware" again. Note: Website search can't currently find it, its in the downloads for the specific DK.

On older DKs this gets de-activated every time you hold "Reset" button down during power-on sequence and will require a re-upload.

Big indication is "no led lights up" when you connect the USB cable.

RE: nRF52840-DK only executing while debugging

timonsku — Sat, 13 Dec 2025 21:07:19 GMT

It looks like there was some creeping hardware failure, after powering it up again not even the programmer comes up. Power is there but none of the chips are functional. I guess this is a dead board.

RE: nRF52840-DK only executing while debugging

Thomas_1 — Sat, 13 Dec 2025 13:01:22 GMT

Thank you for the fast response. I have tried adding the said config (and a few others I have found online) but after building (with nrf52DK_nrf52832 board) and flashing I still face the same issue. My config:

##############################
# BLE host + Zephyr controller
##############################

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DEVICE_NAME="MDBT42V_TEST"
CONFIG_BT_DEVICE_APPEARANCE=0
CONFIG_BT_EXT_ADV=n
CONFIG_BT_PRIVACY=n
CONFIG_BT_SETTINGS=n

# Use Zephyr split LL controller
CONFIG_BT_LL_SW_SPLIT=y
CONFIG_BT_HCI=y

##############################
# Logging via RTT
##############################

CONFIG_LOG=y
CONFIG_LOG_DEFAULT_LEVEL=3
CONFIG_LOG_PRINTK=y

CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y
CONFIG_LOG_BACKEND_UART=n

CONFIG_CONSOLE=y
CONFIG_STDOUT_CONSOLE=y
CONFIG_PRINTK=y
CONFIG_RTT_CONSOLE=y
CONFIG_UART_CONSOLE=n

##############################
# Clocks – internal LFRC (no 32k XTAL wired)
##############################

CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION=y

##############################
# Power mgmt OFF for debugging
##############################

CONFIG_PM=n
CONFIG_PM_DEVICE=n

##############################
# Basic debug
##############################

CONFIG_ASSERT=y
CONFIG_DEBUG_OPTIMIZATIONS=y  

My code:

#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/hci.h>
#include <hal/nrf_power.h>

LOG_MODULE_REGISTER(test1, LOG_LEVEL_INF);

static void log_reset_reason(void)
{
    uint32_t r = nrf_power_resetreas_get(NRF_POWER);
    nrf_power_resetreas_clear(NRF_POWER, 0xFFFFFFFF);

    printk("RESETREAS = 0x%08x\n", r);
}

void main(void)
{
    int err;

    printk(">>> ENTER main()\n");
    log_reset_reason();

    k_sleep(K_MSEC(1000));   // 1 second delay
    printk("After delay\n");

    printk("Before bt_enable()\n");
    err = bt_enable(NULL);
    printk("After bt_enable()\n");

    if (err) {
        printk("bt_enable failed (err %d)\n", err);
        return;
    }

    printk("Bluetooth enabled\n");

    const struct bt_data ad[] = {
        BT_DATA_BYTES(BT_DATA_FLAGS,
                      (BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR)),
        BT_DATA(BT_DATA_NAME_COMPLETE,
                CONFIG_BT_DEVICE_NAME,
                sizeof(CONFIG_BT_DEVICE_NAME) - 1),
    };

    printk("Before bt_le_adv_start()\n");

    err = bt_le_adv_start(BT_LE_ADV_CONN,
                          ad, ARRAY_SIZE(ad),
                          NULL, 0);

    printk("After bt_le_adv_start()\n");

    if (err) {
        printk("bt_le_adv_start failed (err %d)\n", err);
        return;
    }

    printk("Advertising as \"%s\"\n", CONFIG_BT_DEVICE_NAME);

    while (1) {
        printk("Alive\n");
        k_sleep(K_SECONDS(1));
    }
}

I have connected Clock, Data, VDD, VTG, GND and GND Detect of the DK to Clock, Data, VDD and GND of my MDBT42V module (with built in nrf52832)

RE: nRF52840-DK only executing while debugging

Vidar Berg — Fri, 12 Dec 2025 12:32:13 GMT

Hello,

The symptom you describe is typically seen on custom board designs that don't include the optional 32 kHz crystal or DCDC inductors but have been programmed with a FW image that tries to use the crystal oscillator or DCDC regulator. I would not expect to see this on a DK. As a test, please try to add CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y to the project configuration (prj.conf) to see if that changes anything. This changes the clock source from the default 32KHz crystal oscillator to the internal RC oscillator of the chip.

Best regards,

Vidar

RE: nRF52840-DK only executing while debugging

Thomas_1 — Thu, 11 Dec 2025 20:22:42 GMT

I have the same issue with my MDBT42V module (has nrf52832 chip but not external quartz clock but datasheet says its not needed even for BLE for this module) that I am programming with my nrf52-DK. it only executes while Debugging (but if i plug out Clock and Data WHILE debugging (using JLink RTTViewer) it keeps working until I power cycle (turn power on and off) (flashing and reading works perfectly fine)