Agent Skills: Zephyr RTOS Knowledge Patch

Zephyr RTOS Knowledge Patch

Use this skill when maintaining Zephyr applications, boards, drivers, modules, or tooling where current APIs, Kconfig symbols, Devicetree bindings, build behavior, or subsystem contracts matter.

Working method

1. Read the project's manifest, module revisions, board target, overlays, and configuration before applying guidance.
2. Identify the subsystem being changed and open the matching reference below.
3. Apply migration notes only when the project's selected Zephyr revision includes the change. Treat project source, generated Devicetree, Kconfig diagnostics, and tests as authoritative.
4. Search application code, out-of-tree drivers, bindings, board definitions, CI commands, and sysbuild configuration for both removed and replacement names.
5. Reconfigure from a pristine build directory after Kconfig, Devicetree, board-target, toolchain, or sysbuild changes.
6. Build every affected board qualifier and image, then run relevant Twister, ztest, hardware, networking, security, and upgrade tests.

Reference index

| Reference | Topics | | --- | --- | | Application subsystems and services | Zbus, logging, settings, shell, OCPP, CPU metrics, instrumentation, utility libraries, and service APIs | | Bluetooth | Host, controller, HCI, GATT, Mesh, Classic, LE Audio, ISO, pairing, and channel sounding | | Builds, boards, flashing, and testing | Toolchains, west, sysbuild, targets, runners, native simulation, Twister, ztest, and diagnostics | | Devicetree, drivers, and hardware | Bindings, ADC, CAN, clocks, Ethernet hardware, flash, I3C, sensors, SPI, timers, and power | | Graphics, input, stepper, and USB | Displays, LVGL, video, input, haptics, PWM, steppers, USB device, UVC, and USB host | | Kernel, architecture, and core APIs | Kernel, POSIX, scheduling, userspace, architecture ports, memory, runtime PM, and core utilities | | Networking and protocols | Sockets, HTTP, CoAP, DHCP, DNS, Ethernet L2, LwM2M, MQTT, OpenThread, Wi-Fi, and LoRa | | Security, storage, and firmware update | PSA Crypto, Mbed TLS, secure storage, filesystems, MCUboot, MCUmgr, hawkBit, TF-M, and security fixes |

Breaking-change quick reference

Build, boards, and flashing

• Use current hardware-model board targets; the first-generation hardware model and its compatibility aliases are gone.
• Prefer native_sim naming throughout native boards and drivers. Native UART instances use uart_native_pty and zephyr,native-pty-uart.
• Account for runner changes: Nordic boards prefer nRF Util, current STM32 boards may prefer STM32CubeProgrammer, and erase/reset behavior is now more explicit.
• Use application file suffixes and sysbuild_file_suffixes; the old build-type feature is removed.
• Update OpenOCD file selection to --file-type=elf, bin, or hex and use --file for an alternate artifact.
• Require Python 3.12, Zephyr SDK 1.0.0, and C17-capable tooling; temporary C99 and C11 fallbacks are deprecated.
• Add zephyr_generated_headers dependencies to downstream CMake targets that consume generated headers during parallel builds.

Kernel, architecture, and core APIs

• Replace CONFIG_MP_NUM_CPUS with CONFIG_MP_MAX_NUM_CPUS.
• Replace the deprecated pipe API with k_pipe_write(), k_pipe_read(), k_pipe_reset(), and k_pipe_close(); transfer thresholds and dynamic pipe allocation are gone.
• Treat device_init() failures as negative -errno values.
• Use standard POSIX headers rather than <zephyr/posix/...> wrappers, and enable CONFIG_POSIX_API when unprefixed socket names are required.
• Update file-descriptor sizing around ZVFS_OPEN_SIZE and contributed CONFIG_ZVFS_OPEN_ADD_SIZE_* requirements.
• DMA no longer exposes a userspace syscall surface.
• Use min, max, and clamp instead of Z_MIN, Z_MAX, and Z_CLAMP.
• Replace cache-coherence hooks with CONFIG_CACHE_CAN_SAY_MEM_COHERENCE and sys_cache_is_mem_coherent().

Devicetree and driver contracts

• Use DT_REG_ADDR_RAW when an address is used as a Devicetree index; normal register address and size macros now produce unsigned literals.
• Bindings must use hyphenated property names and cannot default status, #address-cells, or #size-cells.
• Use plural power-domains, declare #power-domain-cells, and use power-domain-names for multiple entries.
• Out-of-tree implementations of upstream driver classes must declare their iterable-section API with DEVICE_API().
• Configure PHY link settings through the PHY API and Devicetree rather than removed Ethernet MAC Kconfigs and requests.
• Use driver-specific CAN filter limits and Devicetree mailbox counts instead of removed generic capacity options.
• For 64-bit counter values, select both driver support and application use with the corresponding counter Kconfigs.
• RISC-V platforms require a riscv Devicetree node with riscv,isa-base and riscv,isa-extensions.

Security, storage, and update

• Pass MCUboot imgtool arguments through CONFIG_MCUBOOT_EXTRA_IMGTOOL_ARGS; the build no longer invokes west sign for MCUboot.
• Set CONFIG_TFM_IMAGE_SECURITY_COUNTER explicitly rather than deriving the rollback counter from the image version.
• Use PSA Crypto paths. TinyCrypt is removed, and current Mbed TLS provides TLS/X.509 while TF-PSA-Crypto provides cryptography.
• Explicitly select secure-storage backend dependencies; settings, NVS, ZMS, and related storage are not implied.
• Preserve installed secure-storage data with CONFIG_SECURE_STORAGE_64_BIT_UID when compatibility with old 64-bit UIDs is required.
• Size stream_flash_init() explicitly; zero no longer discovers capacity.
• Use authenticated hawkBit DDI configuration; anonymous mode is removed.
• Treat signed secure and non-secure TF-M BIN outputs as unconfirmed FOTA images and accept them before reboot when appropriate.

Networking and protocols

• Include network buffers from <zephyr/net_buf.h> and update socket-service callbacks to receive struct net_socket_service_event *.
• Update net_mgmt handlers to accept a 64-bit event and decode it with NET_MGMT_LAYER_CODE and NET_MGMT_GET_COMMAND.
• Use net_linkaddr.len == 0 to detect an unset inline link address.
• Pass the new required arguments to CoAP block, HTTP response, ICMP, DNS reconfiguration, MQTT disconnect, and LwM2M APIs.
• Review HTTP service _concurrent, _backlog, _config, and fallback-resource arguments: current service macros honor all of them.
• Update networking identifiers to net_, NET_, and ZSOCK_ forms, and include POSIX socket headers directly when using POSIX APIs.
• Secure sockets enforce their protocol argument as the minimum TLS version; explicitly choose TLS versions and ciphersuites.
• Forwarded IPv4 and IPv6 packets now decrement their TTL or hop limit.

Bluetooth

• Register BAP Unicast Server, Scan Delegator, PACS, and related profiles at runtime before use; enable their dependencies explicitly.
• Rename the codec QoS family to bt_bap_qos_cfg and use BT_BAP_QOS_CFG* constants.
• Restart legacy connectable advertising explicitly when the application relied on automatic resumption; extended advertising never auto-resumes.
• Use the normal driver model for HCI drivers. Current HCI buffers carry the H:4 type in the payload and commands are allocated with bt_hci_cmd_alloc().
• Create and remove ISO data paths explicitly and secure the ACL before connecting an ISO channel.
• Migrate Mesh storage to PSA carefully: incompatible key storage requires unprovisioning and reprovisioning.
• Legacy LE passkey-entry bonds no longer provide MITM authentication.
• Audio foreach callbacks return true to continue and false to stop.

Graphics, input, video, and USB

• Pass user_data through input callback definitions and callbacks; use NULL for context-free behavior.
• Update video code for video_buf_type, bit-based pixel sizes, timeout-aware allocation, video_format.size, and the consolidated stream hook.
• Apply UVC-negotiated format and frame rate to the source device in the application.
• Use uvc_device_init(), uvc_device_add_format(), uvc_device_enable(), and uvc_device_shutdown().
• Migrate stepper motion calls and events to stepper_ctrl_* and STEPPER_CTRL_EVENT_*, and move step/direction motion properties to a controller node.
• Remove display color-format workarounds that depended on earlier RGB/BGR or monochrome inversions.

High-value additions

Platform and developer tooling

• Use dtdoctor, traceconfig, footprint charts, and the build dashboard to investigate configuration and image-size problems.
• Twister supports power measurement and camera-based display validation; ztest includes a benchmark framework with overhead compensation and statistical reporting.
• zephyr_constants_library() can generate C headers from build-time structure layout constants.
• Scope helpers provide RAII/defer-style cleanup in C, and tiered heap hardening adds progressively stronger allocator checks.

Devices and application services

• Standard subsystems now cover secure storage, ZMS, comparators, haptics, steppers, operational amplifiers, NVMEM, OTP, biometrics, and wake-up controllers.
• Zbus provides heapless runtime observers, asynchronous listeners, and experimental IPC proxy agents.
• CPU load metrics, pressure-based frequency policy, and compiler-assisted instrumentation support profiling and adaptive performance.
• The OCPP library supplies charge-point authorization, transaction, and meter operations over WebSocket.

Connectivity and firmware management

• Networking adds WireGuard, Wi-Fi Direct, MQTT 5, secure CoAP services, HTTP compression, FTP, richer DNS records, and asynchronous SNTP.
• MCUmgr adds discovery, slot information, LoRaWAN, UDP/DTLS, raw UART, and firmware-updater flows.
• MCUboot supports offset swap, RAM-load and firmware-loader compositions, SHA-512, compressed LZMA2 images, and direct-XIP slot variants.
• Bluetooth adds Classic HFP roles, LE Audio group management, Alert Notification Service, callback unregistration, and Mesh key synchronization.

Validation checklist

• Re-run CMake configuration after changing board targets, qualifiers, module manifests, Kconfig, Devicetree, snippets, or sysbuild composition.
• Compile every code path affected by callback signatures, structure layout, enum values, constness, or renamed symbols.
• Validate generated Devicetree and Kconfig values rather than assuming an old default still applies.
• Test bootloader upgrades and storage migrations on copies of installed data, including rollback counters, partition layouts, key formats, and image confirmation.
• Exercise networking and Bluetooth teardown, retry, timeout, resumption, and security paths, not only successful setup.
• Run unit tests, Twister scenarios, and hardware tests appropriate to each changed subsystem.