merged.hex only updated on pristine build?

tc531

Is it normal behaviour that the merged.hex file I send to my target is only updated on pristine builds? These take ages.

I’m testing this on the blinky sample, but others also do the same. I’ve tried regenerating the build several times, updating west and reinstalling tool chains.

If I edit main.c and just run “build” in VS Code, it creates a new zephyr.elf but never calls the command to update merged.hex.

Having to do a pristine build for every code change is too painful..

jaredwolff

Hey @tc531 it should update every build (if there’s a change)

tc531

OK thanks. Something is broken then in my VS Code West World.

jaredwolff

Sometimes deleting your build folder resolves things like this. You are using Nordic’s plugin right?

tc531

Deleting the build folder made no difference, and my colleague is reporting the same problem on his PC. We’re using nRF Connect for VS Code, version 2025.9.798.

jaredwolff

What OS are you running @tc531? Windows? I recommend getting started with this guide. Making sure you can build the samples. Then, moving to a custom application.

tc531

Hi Jared, yes, Windows.

I re-installed pretty much everything I had Nordic-related on my PC, and went through your install instructions.

Again, merged.hex does not get updated unless the pristine build option is selected.

Pristine build:

Generating files from C:/nfed/nfed/samples/blinky/build/blinky/zephyr/zephyr.elf for board: circuitdojo_feather_nrf9151
image.py: sign the payload
image.py: sign the payload
[11/20] Performing build step for 'mcuboot'
[6/214] Generating include/generated/zephyr/version.h
-- Zephyr version: 4.0.99 (C:/nfed/zephyr), build: v4.0.99-ncs1-1
[214/214] Linking C executable zephyr\zephyr.elf
Memory region         Used Size  Region Size  %age Used
           FLASH:       47040 B        48 KB     95.70%
             RAM:       22720 B        32 KB     69.34%
        IDT_LIST:          0 GB        32 KB      0.00%
Generating files from C:/nfed/nfed/samples/blinky/build/mcuboot/zephyr/zephyr.elf for board: circuitdojo_feather_nrf9151
**[20/20] Generating ../merged.hex**
 *  Terminal will be reused by tasks, press any key to close it.

Normal build after main.c edit:

Building blinky
west build --build-dir c:/nfed/nfed/samples/blinky/build --domain blinky

-- west build: building domain(s): blinky
[0/16] Performing build step for 'tfm'
ninja: no work to do.
[8/8] Linking C executable zephyr\zephyr.elf
Memory region         Used Size  Region Size  %age Used
           FLASH:       37400 B       448 KB      8.15%
             RAM:        8456 B     211608 B      4.00%
        IDT_LIST:          0 GB        32 KB      0.00%
Generating files from C:/nfed/nfed/samples/blinky/build/blinky/zephyr/zephyr.elf for board: circuitdojo_feather_nrf9151
image.py: sign the payload
image.py: sign the payload
 *  Terminal will be reused by tasks, press any key to close it.

We have 3 “problems listed”. I think it’s something to do with MCUBOOT not building.


[{
	"resource": "/c:/nfed/nfed/samples/blinky/boards/circuitdojo_feather_nrf9151_ns.conf",
	"owner": "kconfig",
	"severity": 4,
	"message": "CONFIG_LED_NPM1300 was assigned the value y, but got the value n. Missing dependencies:\nDT_HAS_NORDIC_NPM1300_LED_ENABLED",
	"startLineNumber": 10,
	"startColumn": 1,
	"endLineNumber": 10,
	"endColumn": 19,
	"origin": "extHost1"
},{
	"resource": "/c:/nfed/nfed/samples/blinky/build/blinky/zephyr/.config.sysbuild",
	"owner": "kconfig",
	"severity": 4,
	"message": "CONFIG_UPDATEABLE_IMAGE_NUMBER couldn't be set. Missing dependencies:\n((BOARD_THINGY53_NRF5340_CPUAPP || BOARD_THINGY53_NRF5340_CPUAPP_NS) && SOC_SERIES_NRF53X && NCS_SAMPLE_MCUMGR_BT_OTA_DFU) || (!MCUBOOT && IMG_MANAGER)",
	"startLineNumber": 7,
	"startColumn": 1,
	"endLineNumber": 7,
	"endColumn": 31,
	"origin": "extHost1"
},{
	"resource": "/c:/nfed/nfed/samples/blinky/build/blinky/zephyr/.config.sysbuild",
	"owner": "kconfig",
	"severity": 4,
	"message": "CONFIG_MCUBOOT_UPDATE_FOOTER_SIZE couldn't be set. Missing dependencies:\nMCUBOOT_IMG_MANAGER && IMG_MANAGER",
	"startLineNumber": 25,
	"startColumn": 1,
	"endLineNumber": 25,
	"endColumn": 34,
	"origin": "extHost1"
}]

jaredwolff

Again, merged.hex does not get updated unless the pristine build option is selected.

Are you sure you’re editing the correct main.c. I’m guilty of editing the wrong one. 😃 (There’s at least one other blinkly sample in the Zephyr samples directory) Also, merged.hex is only generated when sysbuild is enabled. According to your logs, it appears sysbuild is not enabled. There should be a --sysbuild at the end of the west build command.

You also need sysbuild.conf with SB_CONFIG_BOOTLOADER_MCUBOOT=y and sysbuild/mcuboot.conf with:

# Disable Zephyr console
CONFIG_CONSOLE=n

# Multithreading
CONFIG_MULTITHREADING=y

# MCUBoot settings
CONFIG_BOOT_MAX_IMG_SECTORS=256

This is especially important if you want to have OTA in your final application. The nfed blinky sample does have this setup already.

Once you have that setup correctly, it will only be changed if you’ve made code changes (if built previously & successfully) or if you do a pristine build.

tc531

I keep selecting “Use sysbuild” when I add a build configuration, but the change does not seem to get applied when I generate the build. I’m editing the correct main.c.

jaredwolff

Hmm I’ve seen this before. sysbuild will only apply on a successful build. Is your build failing after selecting “Generate and Build”?

tc531

Problem solved. What happens on Build depends entirely on which “Blinky” you have selected in the VS Code Applications pane. Top level: it’s OK and builds merged.hex. Lower level Blinky: MCU_BOOT does not get built and merged. SIgh. Thanks for your help.