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