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1 | This is an explanation of what i2c is, and what is supported in this package. |
2 | ||
3 | I2C and SMBus | |
4 | ============= | |
5 | ||
6 | I2C (pronounce: I squared C) is a protocol developed by Philips. It is a | |
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7 | slow two-wire protocol (variable speed, up to 400 kHz), with a high speed |
8 | extension (3.4 MHz). It provides an inexpensive bus for connecting many | |
9 | types of devices with infrequent or low bandwidth communications needs. | |
10 | I2C is widely used with embedded systems. Some systems use variants that | |
11 | don't meet branding requirements, and so are not advertised as being I2C. | |
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13 | SMBus (System Management Bus) is based on the I2C protocol, and is mostly |
14 | a subset of I2C protocols and signaling. Many I2C devices will work on an | |
15 | SMBus, but some SMBus protocols add semantics beyond what is required to | |
16 | achieve I2C branding. Modern PC mainboards rely on SMBus. The most common | |
17 | devices connected through SMBus are RAM modules configured using I2C EEPROMs, | |
18 | and hardware monitoring chips. | |
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20 | Because the SMBus is mostly a subset of the generalized I2C bus, we can |
21 | use its protocols on many I2C systems. However, there are systems that don't | |
22 | meet both SMBus and I2C electrical constraints; and others which can't | |
23 | implement all the common SMBus protocol semantics or messages. | |
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24 | |
25 | ||
26 | Terminology | |
27 | =========== | |
28 | ||
29 | When we talk about I2C, we use the following terms: | |
30 | Bus -> Algorithm | |
31 | Adapter | |
32 | Device -> Driver | |
33 | Client | |
34 | ||
35 | An Algorithm driver contains general code that can be used for a whole class | |
36 | of I2C adapters. Each specific adapter driver depends on one algorithm | |
37 | driver. | |
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39 | A Driver driver (yes, this sounds ridiculous, sorry) contains the general |
40 | code to access some type of device. Each detected device gets its own | |
41 | data in the Client structure. Usually, Driver and Client are more closely | |
42 | integrated than Algorithm and Adapter. | |
43 | ||
44 | For a given configuration, you will need a driver for your I2C bus (usually | |
45 | a separate Adapter and Algorithm driver), and drivers for your I2C devices | |
46 | (usually one driver for each device). There are no I2C device drivers | |
47 | in this package. See the lm_sensors project http://www.lm-sensors.nu | |
48 | for device drivers. | |
49 | ||
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50 | At this time, Linux only operates I2C (or SMBus) in master mode; you can't |
51 | use these APIs to make a Linux system behave as a slave/device, either to | |
52 | speak a custom protocol or to emulate some other device. | |
53 | ||
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54 | |
55 | Included Bus Drivers | |
56 | ==================== | |
57 | Note that only stable drivers are patched into the kernel by 'mkpatch'. | |
58 | ||
59 | ||
60 | Base modules | |
61 | ------------ | |
62 | ||
63 | i2c-core: The basic I2C code, including the /proc/bus/i2c* interface | |
64 | i2c-dev: The /dev/i2c-* interface | |
65 | i2c-proc: The /proc/sys/dev/sensors interface for device (client) drivers | |
66 | ||
67 | Algorithm drivers | |
68 | ----------------- | |
69 | ||
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70 | i2c-algo-bit: A bit-banging algorithm |
71 | i2c-algo-pcf: A PCF 8584 style algorithm | |
72 | i2c-algo-ibm_ocp: An algorithm for the I2C device in IBM 4xx processors (NOT BUILT BY DEFAULT) | |
73 | ||
74 | Adapter drivers | |
75 | --------------- | |
76 | ||
77 | i2c-elektor: Elektor ISA card (uses i2c-algo-pcf) | |
78 | i2c-elv: ELV parallel port adapter (uses i2c-algo-bit) | |
79 | i2c-pcf-epp: PCF8584 on a EPP parallel port (uses i2c-algo-pcf) (NOT mkpatched) | |
80 | i2c-philips-par: Philips style parallel port adapter (uses i2c-algo-bit) | |
81 | i2c-adap-ibm_ocp: IBM 4xx processor I2C device (uses i2c-algo-ibm_ocp) (NOT BUILT BY DEFAULT) | |
82 | i2c-pport: Primitive parallel port adapter (uses i2c-algo-bit) | |
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83 | i2c-velleman: Velleman K8000 parallel port adapter (uses i2c-algo-bit) |
84 |