.. _smbus_api:

System Management Bus (SMBus)
#############################

.. contents::
    :local:
    :depth: 2

Overview
********

System Management Bus (SMBus) is derived from  I2C for communication
with devices on the motherboard. A system may use SMBus to communicate
with the peripherals on the motherboard without using dedicated control
lines. SMBus peripherals can provide various manufacturer information,
report errors, accept control parameters, etc.

Devices on the bus can operate in three roles: as a Controller that
initiates transactions and controls the clock, a Peripheral that
responds to transaction commands, or a Host, which is a specialized
Controller, that provides the main interface to the system's CPU.
Zephyr has API for the Controller role.

SMBus peripheral devices can initiate communication with Controller
with two methods:

* **Host Notify protocol**: Peripheral device that supports the Host Notify
  protocol behaves as a Controller to perform the notification. It writes
  a three-bytes message to a special address "SMBus Host (0x08)" with own
  address and two bytes of relevant data.
* **SMBALERT# signal**: Peripheral device uses special signal SMBALERT# to
  request attention from the Controller. The Controller needs to read one byte
  from the special "SMBus Alert Response Address (ARA) (0x0c)". The peripheral
  device responds with a data byte containing its own address.

Currently, the API is based on `SMBus Specification`_ version 2.0

.. note::
   See :ref:`coding_guideline_inclusive_language` for information about
   the terminology used in this API.

.. _smbus-controller-api:

SMBus Controller API
********************

Zephyr's SMBus controller API is used when an SMBus device controls the bus,
particularly the start and stop conditions and the clock.  This is
the most common mode used to interact with SMBus peripherals.

Configuration Options
*********************

Related configuration options:

* :kconfig:option:`CONFIG_SMBUS`

API Reference
*************

.. doxygengroup:: smbus_interface

.. _SMBus Specification: https://smbus.org/specs/smbus20.pdf
