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-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
- 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).
-At this time, Linux only operates I2C (or SMBus) in master mode; you can't
-use these APIs to make a Linux system behave as a slave/device, either to
-speak a custom protocol or to emulate some other device.