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source/source-language.rst
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Grant Likely
Editorial and typesetting fixes for v0.1
18 май 2016, 15:06
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.. _chapter-devicetree-source-format:

Devicetree Source Format (version 1)
================================================

The Devicetree Source (DTS) format is a textual representation of a
devicetree in a form that can be processed by dtc into a binary
devicetree in the form expected by the kernel. The following description is
not a formal syntax definition of DTS, but describes the basic
constructs used to represent devicetrees.

Node and property definitions
-----------------------------

Devicetree nodes are defined with a node name and unit address with
braces marking the start and end of the node definition. They may be
preceded by a label.

::

    [label:] node-name[@unit-address] {
        [properties definitions]
        [child nodes]
    }

Nodes may contain property definitions and/or child node definitions. If
both are present, properties shall come before child nodes.

Property definitions are name value pairs in the form:

::

        [label:] property-name = value;

except for properties with empty (zero length) value which have the
form:

::

        [label:] property-name;

Property values may be defined as an array of 32-bit integer cells, as
null-terminated strings, as bytestrings or a combination of these.

-  Arrays of cells are represented by angle brackets surrounding a space
   separated list of C-style integers. Example:

::

        interrupts = <17 0xc>;

-  A 64-bit value is represented with two 32-bit cells. Example:

::

        clock-frequency = <0x00000001 0x00000000>;

-  A null-terminated string value is represented using double quotes
   (the property value is considered to include the terminating NULL
   character). Example:

::

        compatible = "simple-bus";

-  A bytestring is enclosed in square brackets [ ] with each byte
   represented by two hexadecimal digits. Spaces between each byte are
   optional. Example:

::

        local-mac-address = [00 00 12 34 56 78];

or equivalently:

::

        local-mac-address = [000012345678];

-  Values may have several comma-separated components, which are
   concatenated together. Example:

::

        compatible = "ns16550", "ns8250";
        example = <0xf00f0000 19>, "a strange property format";

-  In a cell array a reference to another node will be expanded to that
   node’s phandle. References may be & followed by a node’s label.
   Example:

::

        interrupt-parent = < &mpic >;

or they may be & followed by a node’s full path in braces. Example:

::

        interrupt-parent = < &{/soc/interrupt-controller@40000} >;

-  Outside a cell array, a reference to another node will be expanded to
   that node’s full path. Example:

::

        ethernet0 = &EMAC0;

-  Labels may also appear before or after any component of a property
   value, or between cells of a cell array, or between bytes of a
   bytestring. Examples:

::

        reg = reglabel: <0 sizelabel: 0x1000000>;
        prop = [ab cd ef byte4: 00 ff fe];
        str = start: "string value" end: ;

File layout
-----------

**Version 1 DTS files have the overall layout:**

::

    /dts-v1/;
    [memory reservations]
        / {
            [property definitions]
            [child nodes]
        };

The /dts-v1/; shall be present to identify the file as a version 1 DTS
(dts files without this tag will be treated by dtc as being in the
obsolete version 0, which uses a different format for integers in
addition to other small but incompatible changes).

Memory reservations define an entry for the devicetree blob’s memory
reservation table. They have the form: e.g., /memreserve/ <address>
<length>; Where <address> and <length> are 64-bit C-style integers.

*  The / { }; section defines the root node of the devicetree.

*  C style (/* ... \*/) and C++ style (//) comments are supported.