|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.
|When we talk about I2C, we use the following terms:
| Bus -> Algorithm
| Device -> Driver
|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).