Zephyr

Zephyr supplies the RTOS kernel, drivers, board descriptions, shell, filesystems, and build tools used by K-FSW. Its native simulator runs the application on Linux for service and integration tests.

Kconfig selects software; devicetree selects devices and wiring. This lets the same services run on different MCU vendors without embedding board names in service code.

K-FSW currently uses Zephyr APIs directly. Reusing modules and services on another RTOS requires porting their kernel, device, storage, and build dependencies as well as the platform layer.

Kernel use

Primitive	K-FSW use
Thread	Router, service workers, shell, application
Mutex	Shared parameter, persistence, storage, and client state
Workqueue	Deferred device work such as button debounce
Timeout and sleep	Bounded waits and periodic work
Spinlock	Short event-ring updates

Calls that wait on a mutex, the filesystem or the network must run in a thread. Check each public API before calling it from an ISR. UART reception ingests bytes and leaves packet routing to the CSP router thread.

See Zephyr's threads and mutexes.

Devices

Devicetree identifies an instance; Zephyr creates its struct device. Check device_is_ready() before using the driver API.

For example, a chosen UART selects the device consumed by the KISS adapter. A chosen flash partition selects the LittleFS volume. K-FSW services use Zephyr's filesystem calls once storage is mounted.

See the device model.

Kconfig

Configuration is combined at build time:

app/prj.conf
  + app/boards/<board>.conf
  + optional profile .conf
  -> build/<target>/zephyr/.config

CONFIG_KFSW_* symbols select services and their startup and shell code. Dependencies are checked by Kconfig: remote parameters need PARAM and CSP; FTP needs CSP and storage.

Inspect the generated result from the workspace root:

rg '^CONFIG_KFSW_' build/linux/zephyr/.config

Change the source .conf or Kconfig file and rebuild. See the Kconfig guide.

Devicetree

Use overlays for hardware instances, pins, baud rates, and flash regions. The NUCLEO UART/KISS profile uses:

Kconfig:     CONFIG_KFSW_CSP_KISS_UART=y
chosen:      kfsw,csp-uart = &usart3
UART:        PD8/PD9, 115200 baud, 8N1

kfsw,storage-partition selects the storage partition. Multi-link profiles declare separate named interfaces; see CSP and links.

Inspect build/<target>/zephyr/zephyr.dts to confirm the final hardware description. See the devicetree guide and overlay how-to.

Boards and K-FSW targets

K-FSW target	Zephyr board
`linux`	`native_sim/native/64`
`nucleo_l496zg`	`nucleo_l496zg`
`frdm_k64f`	`frdm_k64f/mk64f12`
`rpi_pico_w`	`rpi_pico/rp2040/w`

config/targets/<target>.env maps the target to its board and tool defaults. Board configuration and overlays live under app/boards/; optional compositions live under config/profiles/.

See Boards and targets for supported features and bench results. For new hardware, start with Zephyr's board-porting guide.

west

west update checks out the revisions in west.yml. west build, west flash, and west debug invoke Zephyr's tooling.

From the workspace root:

. .venv/bin/activate
west manifest --validate
west update

Preserve local dependency changes before updating. Detached HEAD at a manifest SHA is expected; Contributing covers dependency branches.

See the west guide.

Build output

CMake resolves the board, Kconfig, devicetree, and module sources; Ninja compiles and links the image.

File under `build/<target>/`	Use
`zephyr/.config`	Resolved software selection
`zephyr/zephyr.dts`	Resolved devices and wiring
`zephyr/include/generated/`	Generated configuration headers
`compile_commands.json`	Compiler flags, include paths, IntelliSense
`zephyr/zephyr.elf`	Symbols and source debugging

Regenerate these files by rebuilding. See the CMake build guide.

Table of Contents