This is the documentation for the latest (main) development branch of Zephyr. If you are looking for the documentation of previous releases, use the drop-down menu on the left and select the desired version.

Glossary of Terms

API

(Application Program Interface) A defined set of routines and protocols for building application software.

application

The set of user-supplied files that the Zephyr build system uses to build an application image for a specified board configuration. It can contain application-specific code, kernel configuration settings, and at least one CMakeLists.txt file. The application’s kernel configuration settings direct the build system to create a custom kernel that makes efficient use of the board’s resources. An application can sometimes be built for more than one type of board configuration (including boards with different CPU architectures), if it does not require any board-specific capabilities.

application image

A binary file that is loaded and executed by the board for which it was built. Each application image contains both the application’s code and the Zephyr kernel code needed to support it. They are compiled as a single, fully-linked binary. Once an application image is loaded onto a board, the image takes control of the system, initializes it, and runs as the system’s sole application. Both application code and kernel code execute as privileged code within a single shared address space.

architecture

An instruction set architecture (ISA) along with a programming model.

board

A target system with a defined set of devices and capabilities, which can load and execute an application image. It may be an actual hardware system or a simulated system running under QEMU. A board can contain one or more SoCs. The Zephyr kernel supports a variety of boards.

board configuration

A set of kernel configuration options that specify how the devices present on a board are used by the kernel. The Zephyr build system defines one or more board configurations for each board it supports. The kernel configuration settings that are specified by the build system can be over-ridden by the application, if desired.

board name

The human-readable name of a board. Uniquely and descriptively identifies a particular system, but does not include additional information that may be required to actually build a Zephyr image for it. See Board terminology for additional details.

board qualifiers

The set of additional tokens, separated by a forward slash (/) that follow the board name (and optionally board revision) to form the board target. The currently accepted qualifiers are SoC, CPU cluster and variant. See Board terminology for additional details.

board revision

An optional version string that identifies a particular revision of a hardware system. This is useful to avoid duplication of board files whenever small changes are introduced to a hardware system. See Multiple board revisions and Building for a board revision for more information.

board target

The full string that can be provided to any of the Zephyr build tools to compile and link an image for a particular hardware system. This string uniquely identifies the combination of board name, board revision and board qualifiers. See Board terminology for additional details.

CPU cluster

A group of one or more CPU cores, all executing the same image within the same address space and in a symmetrical (SMP) configuration. Only CPU cores of the same architecture can be in a single cluster. Multiple CPU clusters (each of one or more cores) can coexist in the same SoC.

CPU core

A single processing unit, with its own Program Counter, executing program instructions sequentially. CPU cores are part of a CPU cluster, which can contain one or more cores.

device runtime power management

Device Runtime Power Management (PM) refers the capability of devices to save energy independently of the system power state. Devices will keep reference of their usage and will automatically be suspended or resumed. This feature is enabled via the CONFIG_PM_DEVICE_RUNTIME Kconfig option.

idle thread

A system thread that runs when there are no other threads ready to run.

IDT

(Interrupt Descriptor Table) a data structure used by the x86 architecture to implement an interrupt vector table. The IDT is used to determine the correct response to interrupts and exceptions.

ISR

(Interrupt Service Routine) Also known as an interrupt handler, an ISR is a callback function whose execution is triggered by a hardware interrupt (or software interrupt instructions) and is used to handle high-priority conditions that require interrupting the current code executing on the processor.

kernel

The set of Zephyr-supplied files that implement the Zephyr kernel, including its core services, device drivers, network stack, and so on.

power domain

A power domain is a collection of devices for which power is applied and removed collectively in a single action. Power domains are represented by device.

power gating

Power gating reduces power consumption by shutting off areas of an integrated circuit that are not in use.

SoC

A System on a chip, that is, an integrated circuit that contains at least one CPU cluster (in turn with at least one CPU core), as well as peripherals and memory.

SoC family

One or more SoCs or SoC series that share enough in common to consider them related and under a single family denomination.

SoC series

A number of different SoCs that share similar characteristics and features, and that the vendor typically names and markets together.

subsystem

A subsystem refers to a logically distinct part of the operating system that handles specific functionality or provides certain services.

system power state

System power states describe the power consumption of the system as a whole. System power states are represented by pm_state.

variant

In the context of board qualifiers, a variant designates a particular type or configuration of a build for a combination of SoC and CPU cluster. Common uses of the variant concept include introducing both secure and non-secure builds for platforms with Trusted Execution Environment support, or selecting the type of RAM used in a build.

west

A multi-repo meta-tool developed for the Zephyr project. See West (Zephyr’s meta-tool).

west installation

An obsolete term for a west workspace used prior to west 0.7.

west manifest

A YAML file, usually named west.yml, which describes projects, or the Git repositories which make up a west workspace, along with additional metadata. See Basics for general information and West Manifests for details.

west manifest repository

The Git repository in a west workspace which contains the west manifest. Its location is given by the manifest.path configuration option. See Basics.

west workspace

A directory on your system with a .west subdirectory and a west manifest repository. You clone the Zephyr source code onto your system by creating a west workspace using the west init command. See Basics.

XIP

(eXecute In Place) a method of executing programs directly from long term storage rather than copying it into RAM, saving writable memory for dynamic data and not the static program code.