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Device Tree Source Format (version 1)
=====================================
The Device Tree Source (DTS) format is a textual representation of a
device tree in a form that can be processed by dtc into a binary
device tree in the form expected by the kernel. The description below
is not a formal syntax definition of DTS, but describes the basic
constructs used to represent device trees.
Node and property definitions
-----------------------------
Device tree 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 must 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 8, 16, 32, or 64-bit integer
elements, as NUL-terminated strings, as bytestrings or a combination of these.
* Arrays are represented by angle brackets surrounding a space separated list
of C-style integers or character literals. Array elements default to 32-bits
in size. An array of 32-bit elements is also known as a cell list or a list
of cells. A cell being an unsigned 32-bit integer.
e.g. interrupts = <17 0xc>;
* A 64-bit value can be represented with two 32-bit elements.
e.g. clock-frequency = <0x00000001 0x00000000>;
* The storage size of an element can be changed using the /bits/ prefix. The
/bits/ prefix allows for the creation of 8, 16, 32, and 64-bit elements.
The resulting array will not be padded to a multiple of the default 32-bit
element size.
e.g. interrupts = /bits/ 8 <17 0xc>;
e.g. clock-frequency = /bits/ 64 <0x0000000100000000>;
* A NUL-terminated string value is represented using double quotes
(the property value is considered to include the terminating NUL
character).
e.g. compatible = "simple-bus";
* A bytestring is enclosed in square brackets [] with each byte
represented by two hexadecimal digits. Spaces between each byte are
optional.
e.g. 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.
e.g. compatible = "ns16550", "ns8250";
example = <0xf00f0000 19>, "a strange property format";
* In an array a reference to another node will be expanded to that node's
phandle. References may by '&' followed by a node's label:
e.g. interrupt-parent = < &mpic >;
or they may be '&' followed by a node's full path in braces:
e.g. interrupt-parent = < &{/soc/interrupt-controller@40000} >;
References are only permitted in arrays that have an element size of
32-bits.
* Outside an array, a reference to another node will be expanded to that
node's full path.
e.g. ethernet0 = &EMAC0;
* Labels may also appear before or after any component of a property
value, or between elements of an array, or between bytes of a bytestring.
e.g. reg = reglabel: <0 sizelabel: 0x1000000>;
e.g. prop = [ab cd ef byte4: 00 ff fe];
e.g. 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/;" must 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
amongst other small but incompatible changes).
* Memory reservations define an entry for the device tree 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 device tree.
* C style (/* ... */) and C++ style (// ...) comments are supported.
-- David Gibson <david@gibson.dropbear.id.au>
-- Yoder Stuart <stuart.yoder@freescale.com>
-- Anton Staaf <robotboy@chromium.org>
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