blob: 82c49ba3b7e62617c1001feb74aa699e6703d6ee [file] [log] [blame]
.. _kernel_api:
Kernel Services
###############
The Zephyr kernel lies at the heart of every Zephyr application. It provides
a low footprint, high performance, multi-threaded execution environment
with a rich set of available features. The rest of the Zephyr ecosystem,
including device drivers, networking stack, and application-specific code,
uses the kernel's features to create a complete application.
The configurable nature of the kernel allows you to incorporate only those
features needed by your application, making it ideal for systems with limited
amounts of memory (as little as 2 KB!) or with simple multi-threading
requirements (such as a set of interrupt handlers and a single background task).
Examples of such systems include: embedded sensor hubs, environmental sensors,
simple LED wearable, and store inventory tags.
Applications requiring more memory (50 to 900 KB), multiple communication
devices (like Wi-Fi and Bluetooth Low Energy), and complex multi-threading,
can also be developed using the Zephyr kernel. Examples of such systems
include: fitness wearables, smart watches, and IoT wireless gateways.
Scheduling, Interrupts, and Synchronization
*******************************************
These pages cover basic kernel services related to thread scheduling and
synchronization.
.. toctree::
:maxdepth: 1
threads/index.rst
scheduling/index.rst
threads/system_threads.rst
threads/workqueue.rst
threads/nothread.rst
interrupts.rst
polling.rst
synchronization/semaphores.rst
synchronization/mutexes.rst
synchronization/condvar.rst
synchronization/events.rst
smp/smp.rst
.. _kernel_data_passing_api:
Data Passing
************
These pages cover kernel objects which can be used to pass data between
threads and ISRs.
The following table summarizes their high-level features.
=============== ============== =================== ============== ============== ================= ============== ===============================
Object Bidirectional? Data structure Data item size Data Alignment ISRs can receive? ISRs can send? Overrun handling
=============== ============== =================== ============== ============== ================= ============== ===============================
FIFO No Queue Arbitrary [1] 4 B [2] Yes [3] Yes N/A
LIFO No Queue Arbitrary [1] 4 B [2] Yes [3] Yes N/A
Stack No Array Word Word Yes [3] Yes Undefined behavior
Message queue No Ring buffer Power of two Power of two Yes [3] Yes Pend thread or return -errno
Mailbox Yes Queue Arbitrary [1] Arbitrary No No N/A
Pipe No Ring buffer [4] Arbitrary Arbitrary Yes [5] Yes [5] Pend thread or return -errno
=============== ============== =================== ============== ============== ================= ============== ===============================
[1] Callers allocate space for queue overhead in the data
elements themselves.
[2] Objects added with k_fifo_alloc_put() and k_lifo_alloc_put()
do not have alignment constraints, but use temporary memory from the
calling thread's resource pool.
[3] ISRs can receive only when passing K_NO_WAIT as the timeout
argument.
[4] Optional.
[5] ISRS can send and/or receive only when passing K_NO_WAIT as the
timeout argument.
.. toctree::
:maxdepth: 1
data_passing/queues.rst
data_passing/fifos.rst
data_passing/lifos.rst
data_passing/stacks.rst
data_passing/message_queues.rst
data_passing/mailboxes.rst
data_passing/pipes.rst
.. _kernel_memory_management_api:
Memory Management
*****************
See :ref:`memory_management_api`.
Timing
******
These pages cover timing related services.
.. toctree::
:maxdepth: 1
timing/clocks.rst
timing/timers.rst
Other
*****
These pages cover other kernel services.
.. toctree::
:maxdepth: 1
other/atomic.rst
other/float.rst
other/version.rst
other/fatal.rst
other/thread_local_storage.rst