1.. _introducing_zephyr:
2
3Introduction
4############
5
6The Zephyr OS is based on a small-footprint kernel designed for use on
7resource-constrained and embedded systems: from simple embedded environmental
8sensors and LED wearables to sophisticated embedded controllers, smart
9watches, and IoT wireless applications.
10
11The Zephyr kernel supports multiple architectures, including:
12
13 - ARCv2 (EM and HS) and ARCv3 (HS6X)
14 - ARMv6-M, ARMv7-M, and ARMv8-M (Cortex-M)
15 - ARMv7-A and ARMv8-A (Cortex-A, 32- and 64-bit)
16 - ARMv7-R, ARMv8-R (Cortex-R, 32- and 64-bit)
17 - Intel x86 (32- and 64-bit)
18 - MIPS (MIPS32 Release 1 specification)
19 - NIOS II Gen 2
20 - RISC-V (32- and 64-bit)
21 - SPARC V8
22 - Tensilica Xtensa
23
24The full list of supported boards based on these architectures can be found :ref:`here <boards>`.
25
26Licensing
27*********
28
29Zephyr is permissively licensed using the `Apache 2.0 license`_
30(as found in the ``LICENSE`` file in the
31project's `GitHub repo`_).  There are some
32imported or reused components of the Zephyr project that use other licensing,
33as described in :ref:`Zephyr_Licensing`.
34
35.. _Apache 2.0 license:
36   https://github.com/zephyrproject-rtos/zephyr/blob/main/LICENSE
37
38.. _GitHub repo: https://github.com/zephyrproject-rtos/zephyr
39
40
41Distinguishing Features
42***********************
43
44Zephyr offers a large and ever growing number of features including:
45
46**Extensive suite of Kernel services**
47   Zephyr offers a number of familiar services for development:
48
49   * *Multi-threading Services* for cooperative, priority-based,
50     non-preemptive, and preemptive threads with optional round robin
51     time-slicing. Includes POSIX pthreads compatible API support.
52
53   * *Interrupt Services* for compile-time registration of interrupt handlers.
54
55   * *Memory Allocation Services* for dynamic allocation and freeing of
56     fixed-size or variable-size memory blocks.
57
58   * *Inter-thread Synchronization Services* for binary semaphores,
59     counting semaphores, and mutex semaphores.
60
61   * *Inter-thread Data Passing Services* for basic message queues, enhanced
62     message queues, and byte streams.
63
64   * *Power Management Services* such as overarching, application or
65     policy-defined, System Power Management and fine-grained, driver-defined,
66     Device Power Management.
67
68**Multiple Scheduling Algorithms**
69   Zephyr provides a comprehensive set of thread scheduling choices:
70
71   * Cooperative and Preemptive Scheduling
72   * Earliest Deadline First (EDF)
73   * Meta IRQ scheduling implementing "interrupt bottom half" or "tasklet"
74     behavior
75   * Timeslicing: Enables time slicing between preemptible threads of equal
76     priority
77   * Multiple queuing strategies:
78
79     * Simple linked-list ready queue
80     * Red/black tree ready queue
81     * Traditional multi-queue ready queue
82
83**Highly configurable / Modular for flexibility**
84   Allows an application to incorporate *only* the capabilities it needs as it
85   needs them, and to specify their quantity and size.
86
87**Cross Architecture**
88   Supports a wide variety of :ref:`supported boards<boards>` with different CPU
89   architectures and developer tools. Contributions have added support
90   for an increasing number of SoCs, platforms, and drivers.
91
92**Memory Protection**
93   Implements configurable architecture-specific stack-overflow protection,
94   kernel object and device driver permission tracking, and thread isolation
95   with thread-level memory protection on x86, ARC, and ARM architectures,
96   userspace, and memory domains.
97
98   For platforms without MMU/MPU and memory constrained devices, supports
99   combining application-specific code with a custom kernel to create a
100   monolithic image that gets loaded and executed on a system's hardware. Both
101   the application code and kernel code execute in a single shared address
102   space.
103
104**Compile-time resource definition**
105   Allows system resources to be defined at compile-time, which reduces code
106   size and increases performance for resource-limited systems.
107
108**Optimized Device Driver Model**
109   Provides a consistent device model for configuring the drivers that are part
110   of the platform/system and a consistent model for initializing all the
111   drivers configured into the system and allows the reuse of drivers across
112   platforms that have common devices/IP blocks.
113
114**Devicetree Support**
115   Use of :ref:`devicetree <dt-guide>` to describe hardware.
116   Information from devicetree is used to create the application image.
117
118**Native Networking Stack supporting multiple protocols**
119   Networking support is fully featured and optimized, including LwM2M and BSD
120   sockets compatible support.  OpenThread support (on Nordic chipsets) is also
121   provided - a mesh network designed to securely and reliably connect hundreds
122   of products around the home.
123
124**Bluetooth Low Energy 5.0 support**
125   Bluetooth 5.0 compliant (ESR10) and Bluetooth Low Energy Controller support
126   (LE Link Layer). Includes Bluetooth mesh and a Bluetooth qualification-ready
127   Bluetooth controller.
128
129   * Generic Access Profile (GAP) with all possible LE roles
130   * Generic Attribute Profile (GATT)
131   * Pairing support, including the Secure Connections feature from Bluetooth
132     4.2
133   * Clean HCI driver abstraction
134   * Raw HCI interface to run Zephyr as a Controller instead of a full Host
135     stack
136   * Verified with multiple popular controllers
137   * Highly configurable
138
139   Mesh Support:
140
141   * Relay, Friend Node, Low-Power Node (LPN) and GATT Proxy features
142   * Both Provisioning bearers supported (PB-ADV & PB-GATT)
143   * Highly configurable, fitting in devices with at least 16k RAM
144
145**Native Linux, macOS, and Windows Development**
146   A command-line CMake build environment runs on popular developer OS
147   systems. A native POSIX port lets you build and run Zephyr as a native
148   application on Linux and other OSes, aiding development and testing.
149
150**Virtual File System Interface with ext2, FatFs, and LittleFS Support**
151   ext2, LittleFS and FatFS support; FCB (Flash Circular Buffer) for memory constrained
152   applications.
153
154**Powerful multi-backend logging Framework**
155   Support for log filtering, object dumping, panic mode, multiple backends
156   (memory, networking, filesystem, console, ...) and integration with the shell
157   subsystem.
158
159**User friendly and full-featured Shell interface**
160   A multi-instance shell subsystem with user-friendly features such as
161   autocompletion, wildcards, coloring, metakeys (arrows, backspace, ctrl+u,
162   etc.) and history. Support for static commands and dynamic sub-commands.
163
164**Settings on non-volatile storage**
165   The settings subsystem gives modules a way to store persistent per-device
166   configuration and runtime state. Settings items are stored as key-value pair
167   strings.
168
169**Non-volatile storage (NVS)**
170  NVS allows storage of binary blobs, strings, integers, longs, and any
171  combination of these.
172
173**Native POSIX port**
174  Supports running Zephyr as a Linux application with support for various
175  subsystems and networking.
176
177
178.. include:: ../../README.rst
179   :start-after: start_include_here
180
181
182Fundamental Terms and Concepts
183******************************
184
185See :ref:`glossary`
186