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- I\ :sup:`2`\ C and SMBus Subsystem
- ==================================
- I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
- the "Inter-IC" bus, a simple bus protocol which is widely used where low
- data rate communications suffice. Since it's also a licensed trademark,
- some vendors use another name (such as "Two-Wire Interface", TWI) for
- the same bus. I2C only needs two signals (SCL for clock, SDA for data),
- conserving board real estate and minimizing signal quality issues. Most
- I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
- there's a high speed extension (3.4 MHz) that's not yet found wide use.
- I2C is a multi-master bus; open drain signaling is used to arbitrate
- between masters, as well as to handshake and to synchronize clocks from
- slower clients.
- The Linux I2C programming interfaces support only the master side of bus
- interactions, not the slave side. The programming interface is
- structured around two kinds of driver, and two kinds of device. An I2C
- "Adapter Driver" abstracts the controller hardware; it binds to a
- physical device (perhaps a PCI device or platform_device) and exposes a
- :c:type:`struct i2c_adapter <i2c_adapter>` representing each
- I2C bus segment it manages. On each I2C bus segment will be I2C devices
- represented by a :c:type:`struct i2c_client <i2c_client>`.
- Those devices will be bound to a :c:type:`struct i2c_driver
- <i2c_driver>`, which should follow the standard Linux driver
- model. (At this writing, a legacy model is more widely used.) There are
- functions to perform various I2C protocol operations; at this writing
- all such functions are usable only from task context.
- The System Management Bus (SMBus) is a sibling protocol. Most SMBus
- systems are also I2C conformant. The electrical constraints are tighter
- for SMBus, and it standardizes particular protocol messages and idioms.
- Controllers that support I2C can also support most SMBus operations, but
- SMBus controllers don't support all the protocol options that an I2C
- controller will. There are functions to perform various SMBus protocol
- operations, either using I2C primitives or by issuing SMBus commands to
- i2c_adapter devices which don't support those I2C operations.
- .. kernel-doc:: include/linux/i2c.h
- :internal:
- .. kernel-doc:: drivers/i2c/i2c-boardinfo.c
- :functions: i2c_register_board_info
- .. kernel-doc:: drivers/i2c/i2c-core.c
- :export:
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