diff options
Diffstat (limited to 'Documentation/i2c')
| -rw-r--r-- | Documentation/i2c/i2c_bus.svg | 15 | ||||
| -rw-r--r-- | Documentation/i2c/summary.rst | 79 |
2 files changed, 58 insertions, 36 deletions
diff --git a/Documentation/i2c/i2c_bus.svg b/Documentation/i2c/i2c_bus.svg index 3170de9763..45801de4af 100644 --- a/Documentation/i2c/i2c_bus.svg +++ b/Documentation/i2c/i2c_bus.svg @@ -1,5 +1,6 @@ <?xml version="1.0" encoding="UTF-8" standalone="no"?> <!-- Created with Inkscape (http://www.inkscape.org/) --> +<!-- Updated to inclusive terminology by Wolfram Sang --> <svg xmlns:dc="http://purl.org/dc/elements/1.1/" @@ -1120,7 +1121,7 @@ <rect style="opacity:1;fill:#ffb9b9;fill-opacity:1;stroke:#f00000;stroke-width:2.8125;stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1" id="rect4424-3-2-9-7" - width="112.5" + width="134.5" height="113.75008" x="112.5" y="471.11221" @@ -1133,15 +1134,15 @@ y="521.46259" id="text4349"><tspan sodipodi:role="line" - x="167.5354" + x="178.5354" y="521.46259" style="font-size:25px;line-height:1.25;font-family:sans-serif;text-align:center;text-anchor:middle" id="tspan1273">I2C</tspan><tspan sodipodi:role="line" - x="167.5354" + x="178.5354" y="552.71259" style="font-size:25px;line-height:1.25;font-family:sans-serif;text-align:center;text-anchor:middle" - id="tspan1285">Master</tspan></text> + id="tspan1285">Controller</tspan></text> <rect style="color:#000000;clip-rule:nonzero;display:inline;overflow:visible;visibility:visible;opacity:1;isolation:auto;mix-blend-mode:normal;color-interpolation:sRGB;color-interpolation-filters:linearRGB;solid-color:#000000;solid-opacity:1;fill:#b9ffb9;fill-opacity:1;fill-rule:nonzero;stroke:#006400;stroke-width:2.8125;stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1;color-rendering:auto;image-rendering:auto;shape-rendering:auto;text-rendering:auto;enable-background:accumulate" id="rect4424-3-2-9-7-3-3-5-3" @@ -1171,7 +1172,7 @@ x="318.59131" y="552.08752" style="font-size:25.00000191px;line-height:1.25;font-family:sans-serif;text-align:center;text-anchor:middle;stroke-width:1px" - id="tspan1287">Slave</tspan></text> + id="tspan1287">Target</tspan></text> <path style="fill:none;fill-rule:evenodd;stroke:#000000;stroke-width:1.99968767;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1" d="m 112.49995,677.36223 c 712.50005,0 712.50005,0 712.50005,0" @@ -1233,7 +1234,7 @@ x="468.59131" y="552.08746" style="font-size:25.00000191px;line-height:1.25;font-family:sans-serif;text-align:center;text-anchor:middle;stroke-width:1px" - id="tspan1287-6">Slave</tspan></text> + id="tspan1287-6">Target</tspan></text> <rect style="color:#000000;clip-rule:nonzero;display:inline;overflow:visible;visibility:visible;opacity:1;isolation:auto;mix-blend-mode:normal;color-interpolation:sRGB;color-interpolation-filters:linearRGB;solid-color:#000000;solid-opacity:1;vector-effect:none;fill:#b9ffb9;fill-opacity:1;fill-rule:nonzero;stroke:#006400;stroke-width:2.8125;stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1;color-rendering:auto;image-rendering:auto;shape-rendering:auto;text-rendering:auto;enable-background:accumulate" id="rect4424-3-2-9-7-3-3-5-3-1" @@ -1258,7 +1259,7 @@ x="618.59131" y="552.08746" style="font-size:25.00000191px;line-height:1.25;font-family:sans-serif;text-align:center;text-anchor:middle;stroke-width:1px" - id="tspan1287-9">Slave</tspan></text> + id="tspan1287-9">Target</tspan></text> <path style="fill:none;fill-rule:evenodd;stroke:#000000;stroke-width:1.99968743;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1;marker-end:url(#DotM)" d="m 150,583.61221 v 93.75" diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst index 786c618ba3..579a1c7df2 100644 --- a/Documentation/i2c/summary.rst +++ b/Documentation/i2c/summary.rst @@ -3,29 +3,27 @@ Introduction to I2C and SMBus ============================= I²C (pronounce: I squared C and written I2C in the kernel documentation) 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 +a protocol developed by Philips. It is a two-wire protocol with variable +speed (typically up to 400 kHz, high speed modes up to 5 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, +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 but come under different names, e.g. TWI (Two Wire Interface), IIC. -The latest official I2C specification is the `"I2C-bus specification and user -manual" (UM10204) <https://www.nxp.com/webapp/Download?colCode=UM10204>`_ -published by NXP Semiconductors. However, you need to log-in to the site to -access the PDF. An older version of the specification (revision 6) is archived -`here <https://web.archive.org/web/20210813122132/https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_. +The latest official I2C specification is the `"I²C-bus specification and user +manual" (UM10204) <https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_ +published by NXP Semiconductors, version 7 as of this writing. 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 +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 +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 +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. @@ -33,29 +31,52 @@ implement all the common SMBus protocol semantics or messages. Terminology =========== -Using the terminology from the official documentation, the I2C bus connects -one or more *master* chips and one or more *slave* chips. +The I2C bus connects one or more controller chips and one or more target chips. .. kernel-figure:: i2c_bus.svg - :alt: Simple I2C bus with one master and 3 slaves + :alt: Simple I2C bus with one controller and 3 targets Simple I2C bus -A **master** chip is a node that starts communications with slaves. In the -Linux kernel implementation it is called an **adapter** or bus. Adapter -drivers are in the ``drivers/i2c/busses/`` subdirectory. +A **controller** chip is a node that starts communications with targets. In the +Linux kernel implementation it is also called an "adapter" or "bus". Controller +drivers are usually in the ``drivers/i2c/busses/`` subdirectory. -An **algorithm** contains general code that can be used to implement a -whole class of I2C adapters. Each specific adapter driver either depends on -an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes -its own implementation. +An **algorithm** contains general code that can be used to implement a whole +class of I2C controllers. Each specific controller driver either depends on an +algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes its +own implementation. -A **slave** chip is a node that responds to communications when addressed -by the master. In Linux it is called a **client**. Client drivers are kept -in a directory specific to the feature they provide, for example -``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for +A **target** chip is a node that responds to communications when addressed by a +controller. In the Linux kernel implementation it is also called a "client". +While targets are usually separate external chips, Linux can also act as a +target (needs hardware support) and respond to another controller on the bus. +This is then called a **local target**. In contrast, an external chip is called +a **remote target**. + +Target drivers are kept in a directory specific to the feature they provide, +for example ``drivers/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for video-related chips. -For the example configuration in figure, you will need a driver for your -I2C adapter, and drivers for your I2C devices (usually one driver for each -device). +For the example configuration in the figure above, you will need one driver for +the I2C controller, and drivers for your I2C targets. Usually one driver for +each target. + +Synonyms +-------- + +As mentioned above, the Linux I2C implementation historically uses the terms +"adapter" for controller and "client" for target. A number of data structures +have these synonyms in their name. So, when discussing implementation details, +you should be aware of these terms as well. The official wording is preferred, +though. + +Outdated terminology +-------------------- + +In earlier I2C specifications, controller was named "master" and target was +named "slave". These terms have been obsoleted with v7 of the specification and +their use is also discouraged by the Linux Kernel Code of Conduct. You may +still find them in references to documentation which has not been updated. The +general attitude, however, is to use the inclusive terms: controller and +target. Work to replace the old terminology in the Linux Kernel is on-going. |
