[GitHub/moto-9609/android_kernel_motorola_exynos9610.git] / Documentation / i2c / summary

I2C and SMBus
=============

I2C (pronounce: I squared C) is a protocol developed by Philips. It is a 
slow two-wire protocol (variable speed, up to 400 kHz), with a high speed
extension (3.4 MHz).  It provides an inexpensive bus for connecting many
types of devices with infrequent or low bandwidth communications needs.
I2C is widely used with embedded systems.  Some systems use variants that
don't meet branding requirements, and so are not advertised as being I2C.

SMBus (System Management Bus) is based on the I2C protocol, and is mostly
a subset of I2C protocols and signaling.  Many I2C devices will work on an
SMBus, but some SMBus protocols add semantics beyond what is required to
achieve I2C branding.  Modern PC mainboards rely on SMBus.  The most common
devices connected through SMBus are RAM modules configured using I2C EEPROMs,
and hardware monitoring chips.

Because the SMBus is mostly a subset of the generalized I2C bus, we can
use its protocols on many I2C systems.  However, there are systems that don't
meet both SMBus and I2C electrical constraints; and others which can't
implement all the common SMBus protocol semantics or messages.


Terminology
===========

When we talk about I2C, we use the following terms:
  Bus    -> Algorithm
            Adapter
  Device -> Driver
            Client

An Algorithm driver contains general code that can be used for a whole class
of I2C adapters. Each specific adapter driver either depends on one algorithm
driver, or includes its own implementation.

A Driver driver (yes, this sounds ridiculous, sorry) contains the general
code to access some type of device. Each detected device gets its own
data in the Client structure. Usually, Driver and Client are more closely
integrated than Algorithm and Adapter.

For a given configuration, you will need a driver for your I2C bus, and
drivers for your I2C devices (usually one driver for each device).
Commit	Line	Data
1da177e4 LT	1	I2C and SMBus
	2	=============
	3
	4	I2C (pronounce: I squared C) is a protocol developed by Philips. It is a
4298cfc3 DB	5	slow two-wire protocol (variable speed, up to 400 kHz), with a high speed
	6	extension (3.4 MHz). It provides an inexpensive bus for connecting many
	7	types of devices with infrequent or low bandwidth communications needs.
	8	I2C is widely used with embedded systems. Some systems use variants that
	9	don't meet branding requirements, and so are not advertised as being I2C.
1da177e4	10
4298cfc3 DB	11	SMBus (System Management Bus) is based on the I2C protocol, and is mostly
	12	a subset of I2C protocols and signaling. Many I2C devices will work on an
	13	SMBus, but some SMBus protocols add semantics beyond what is required to
	14	achieve I2C branding. Modern PC mainboards rely on SMBus. The most common
	15	devices connected through SMBus are RAM modules configured using I2C EEPROMs,
	16	and hardware monitoring chips.
1da177e4	17
4298cfc3 DB	18	Because the SMBus is mostly a subset of the generalized I2C bus, we can
	19	use its protocols on many I2C systems. However, there are systems that don't
	20	meet both SMBus and I2C electrical constraints; and others which can't
	21	implement all the common SMBus protocol semantics or messages.
1da177e4 LT	22
	23
	24	Terminology
	25	===========
	26
	27	When we talk about I2C, we use the following terms:
	28	Bus -> Algorithm
	29	Adapter
	30	Device -> Driver
	31	Client
	32
	33	An Algorithm driver contains general code that can be used for a whole class
45ccc6c5 JD	34	of I2C adapters. Each specific adapter driver either depends on one algorithm
45ccc6c5 JD	35	driver, or includes its own implementation.
4298cfc3	36
1da177e4 LT	37	A Driver driver (yes, this sounds ridiculous, sorry) contains the general
	38	code to access some type of device. Each detected device gets its own
	39	data in the Client structure. Usually, Driver and Client are more closely
	40	integrated than Algorithm and Adapter.
	41
45ccc6c5 JD	42	For a given configuration, you will need a driver for your I2C bus, and
45ccc6c5 JD	43	drivers for your I2C devices (usually one driver for each device).