85 lines
3.3 KiB
Plaintext
85 lines
3.3 KiB
Plaintext
This is an explanation of what i2c is, and what is supported in this package.
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I2C and SMBus
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=============
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I2C (pronounce: I squared C) is a protocol developed by Philips. It is a
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slow two-wire protocol (variable speed, up to 400 kHz), with a high speed
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extension (3.4 MHz). It provides an inexpensive bus for connecting many
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types of devices with infrequent or low bandwidth communications needs.
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I2C is widely used with embedded systems. Some systems use variants that
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don't meet branding requirements, and so are not advertised as being I2C.
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SMBus (System Management Bus) is based on the I2C protocol, and is mostly
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a subset of I2C protocols and signaling. Many I2C devices will work on an
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SMBus, but some SMBus protocols add semantics beyond what is required to
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achieve I2C branding. Modern PC mainboards rely on SMBus. The most common
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devices connected through SMBus are RAM modules configured using I2C EEPROMs,
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and hardware monitoring chips.
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Because the SMBus is mostly a subset of the generalized I2C bus, we can
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use its protocols on many I2C systems. However, there are systems that don't
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meet both SMBus and I2C electrical constraints; and others which can't
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implement all the common SMBus protocol semantics or messages.
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Terminology
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===========
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When we talk about I2C, we use the following terms:
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Bus -> Algorithm
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Adapter
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Device -> Driver
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Client
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An Algorithm driver contains general code that can be used for a whole class
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of I2C adapters. Each specific adapter driver depends on one algorithm
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driver.
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A Driver driver (yes, this sounds ridiculous, sorry) contains the general
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code to access some type of device. Each detected device gets its own
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data in the Client structure. Usually, Driver and Client are more closely
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integrated than Algorithm and Adapter.
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For a given configuration, you will need a driver for your I2C bus (usually
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a separate Adapter and Algorithm driver), and drivers for your I2C devices
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(usually one driver for each device). There are no I2C device drivers
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in this package. See the lm_sensors project http://www.lm-sensors.nu
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for device drivers.
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At this time, Linux only operates I2C (or SMBus) in master mode; you can't
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use these APIs to make a Linux system behave as a slave/device, either to
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speak a custom protocol or to emulate some other device.
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Included Bus Drivers
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====================
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Note that only stable drivers are patched into the kernel by 'mkpatch'.
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Base modules
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------------
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i2c-core: The basic I2C code, including the /proc/bus/i2c* interface
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i2c-dev: The /dev/i2c-* interface
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i2c-proc: The /proc/sys/dev/sensors interface for device (client) drivers
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Algorithm drivers
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-----------------
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i2c-algo-bit: A bit-banging algorithm
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i2c-algo-pcf: A PCF 8584 style algorithm
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i2c-algo-ibm_ocp: An algorithm for the I2C device in IBM 4xx processors (NOT BUILT BY DEFAULT)
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Adapter drivers
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---------------
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i2c-elektor: Elektor ISA card (uses i2c-algo-pcf)
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i2c-elv: ELV parallel port adapter (uses i2c-algo-bit)
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i2c-pcf-epp: PCF8584 on a EPP parallel port (uses i2c-algo-pcf) (NOT mkpatched)
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i2c-philips-par: Philips style parallel port adapter (uses i2c-algo-bit)
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i2c-adap-ibm_ocp: IBM 4xx processor I2C device (uses i2c-algo-ibm_ocp) (NOT BUILT BY DEFAULT)
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i2c-pport: Primitive parallel port adapter (uses i2c-algo-bit)
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i2c-velleman: Velleman K8000 parallel port adapter (uses i2c-algo-bit)
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