Compiling the Software

Prerequisite

Make sure the Toolchain is set up as described.

Build Configurations

ZSWatch supports different board targets and logging transports. You combine them when creating a build.

Board Targets

Target	Board string	Description
WatchDK	watchdk@1/nrf5340/cpuapp	Current development kit
ZSWatch Legacy v5	zswatch_legacy@5/nrf5340/cpuapp	Legacy ZSWatch v5 hardware
ZSWatch Legacy v4	zswatch_legacy@4/nrf5340/cpuapp	Legacy ZSWatch v4 hardware
Native simulator	native_sim/native/64	Linux simulator, see Native Simulator

Debug Logging

For debug builds, you need a base config (debug.conf) plus a log transport:

Transport	Kconfig fragment	Overlay needed	Notes
UART	debug.conf, log_on_uart.conf	log_on_uart.overlay	Logs via serial
RTT	debug.conf, log_on_rtt.conf	(none)	Logs via SEGGER RTT (needs J-Link)
USB	debug.conf, log_on_usb.conf	log_on_usb.overlay	Logs via USB CDC ACM

For release builds (no logging, optimized), use release.conf instead of debug.conf.

---

Building

VS Code

1. Open VS Code with the nRF Connect extension.

2. In the nRF Connect sidebar, under Application, select app.

3. Click Add build configuration.

   • Target: Select your board (e.g. watchdk@1/nrf5340/cpuapp).
   • Extra Kconfig fragments: Add the config files, e.g.: debug.conf, log_on_uart.conf
   • Extra Devicetree overlays: Add if needed, e.g.: log_on_uart.overlay
   • Build Directory: Optionally name it, e.g. build_devkit.

   For the native simulator (native_sim/native/64), you also need to add under Extra CMake arguments:

   -DSB_CONF_FILE=sysbuild_no_mcuboot_no_xip.conf

4. Click Generate and Build.

Command Line

Open an nRF Connect Terminal in VS Code (Ctrl+Shift+P → nRF Connect: Create Shell Terminal) and run:

# For example WatchDK with UART debug logging
west build --build-dir app/build_dbg_dk app \
  --board watchdk@1/nrf5340/cpuapp -- \
  -DEXTRA_CONF_FILE="boards/debug.conf;boards/log_on_uart.conf" \
  -DEXTRA_DTC_OVERLAY_FILE="boards/log_on_uart.overlay"

More build examples

# WatchDK with RTT debug (no overlay needed)
west build --build-dir app/build_dbg_dk app \
  --board watchdk@1/nrf5340/cpuapp -- \
  -DEXTRA_CONF_FILE="boards/debug.conf;boards/log_on_rtt.conf"

# Legacy ZSWatch v5 with RTT debug
west build --build-dir app/build_dbg_leg_v5 app \
  --board zswatch_legacy@5/nrf5340/cpuapp -- \
  -DEXTRA_CONF_FILE="boards/debug.conf;boards/log_on_rtt.conf"

# Native simulator (Linux)
west build --build-dir app/build app \
  --board native_sim/native/64 \
  -DSB_CONF_FILE="sysbuild_no_mcuboot_no_xip.conf"

---

Flashing

VS Code

Use the nRF Connect extension: Actions → Flash.

When hovering the Flash button, an icon to the right will appear "Erase and Flash to Board". Use it as it will be much faster.

Command Line

west flash --build-dir app/build_dbg_dk

Without a Debugger

You can flash a locally built firmware over USB without any debugger hardware, using the MCUboot serial bootloader built into ZSWatch.

Enter MCUboot Mode

1. Connect the watch to your computer via USB-C.
2. Hold down the bottom-right button and press the reset button. This enters MCUboot serial recovery mode.

Firmware Images

The dfu_application.zip (found in your build directory or a GitHub release) contains three firmware images:

File	Image	Description
app.internal.bin	App Internal	Main application (app core)
ipc_radio.bin	Net Core	BLE radio firmware (network core)
app.external.bin	App External (XIP)	Code/data stored on external QSPI flash

Web Updater

1. Go to zswatch.dev/update.
2. Choose USB Serial as connection method and click Connect via Serial.
3. Select the USB serial port (appears as ZSWatch BOOT or similar).
4. Under Manual Upload, select dfu_application.zip from your build directory (app/<build_dir>/dfu_application.zip) or from a GitHub release.
5. Click Upload Firmware. The updater will upload all three images in sequence.

mcumgr CLI

Use the mcumgr command-line tool. There are several MCUmgr client tools available, any of them work with similar parameters. The example below uses the Go-based mcumgr:

# Install mcumgr (and Go if needed first)
go install github.com/apache/mynewt-mcumgr-cli/mcumgr@latest

# Extract the firmware zip
unzip app/build_dir/dfu_application.zip -d /tmp/dfu

# Verify connection (use the USB serial port, e.g. /dev/ttyACM0)
mcumgr --conntype serial --connstring dev=/dev/ttyACM0 image list
mcumgr --conntype serial --connstring dev=/dev/ttyACM0,mtu=4096 image upload -e -n 1 /tmp/dfu/app.internal.bin
mcumgr --conntype serial --connstring dev=/dev/ttyACM0,mtu=4096 image upload -e -n 5 /tmp/dfu/app.external.bin

# Upload of the net core image the device needs ~30 seconds to internally
# copy it after upload, so wait before resetting
mcumgr --conntype serial --connstring dev=/dev/ttyACM0,mtu=4096 image upload -e -n 3 /tmp/dfu/ipc_radio.bin
sleep 30

# Reset to boot into the new firmware
mcumgr --conntype serial --connstring dev=/dev/ttyACM0 reset

---

Debugging

For information on debugging, see the Debugging guide.