263 lines
8.6 KiB
Plaintext
263 lines
8.6 KiB
Plaintext
U-boot new uImage source file format (bindings definition)
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==========================================================
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Author: Marian Balakowicz <m8@semihalf.com>
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1) Introduction
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---------------
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Evolution of the 2.6 Linux kernel for embedded PowerPC systems introduced new
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booting method which requires that hardware description is available to the
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kernel in the form of Flattened Device Tree.
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Booting with a Flattened Device Tree is much more flexible and is intended to
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replace direct passing of 'struct bd_info' which was used to boot pre-FDT
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kernels.
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However, U-boot needs to support both techniques to provide backward
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compatibility for platforms which are not FDT ready. Number of elements
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playing role in the booting process has increased and now includes the FDT
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blob. Kernel image, FDT blob and possibly ramdisk image - all must be placed
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in the system memory and passed to bootm as a arguments. Some of them may be
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missing: FDT is not present for legacy platforms, ramdisk is always optional.
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Additionally, old uImage format has been extended to support multi sub-images
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but the support is limited by simple format of the legacy uImage structure.
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Single binary header 'struct image_header' is not flexible enough to cover all
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possible scenarios.
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All those factors combined clearly show that there is a need for new, more
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flexible, multi component uImage format.
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2) New uImage format assumptions
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--------------------------------
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a) Implementation
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Libfdt has been selected for the new uImage format implementation as (1) it
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provides needed functionality, (2) is actively maintained and developed and
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(3) increases code reuse as it is already part of the U-boot source tree.
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b) Terminology
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This document defines new uImage structure by providing FDT bindings for new
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uImage internals. Bindings are defined from U-boot perspective, i.e. describe
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final form of the uImage at the moment when it reaches U-boot. User
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perspective may be simpler, as some of the properties (like timestamps and
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hashes) will need to be filled in automatically by the U-boot mkimage tool.
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To avoid confusion with the kernel FDT the following naming convention is
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proposed for the new uImage format related terms:
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FIT - Flattened uImage Tree
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FIT is formally a flattened device tree (in the libfdt meaning), which
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conforms to bindings defined in this document.
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.its - image tree source
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.itb - image tree blob
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c) Image building procedure
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The following picture shows how the new uImage is prepared. Input consists of
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image source file (.its) and a set of data files. Image is created with the
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help of standard U-boot mkimage tool which in turn uses dtc (device tree
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compiler) to produce image tree blob (.itb). Resulting .itb file is is the
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actual binary of a new uImage.
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tqm5200.its
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+
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vmlinux.bin.gz mkimage + dtc xfer to target
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eldk-4.2-ramdisk --------------> tqm5200.itb --------------> bootm
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tqm5200.dtb /|\
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... |
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'new uImage'
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- create .its file, automatically filled-in properties are omitted
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- call mkimage tool on a .its file
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- mkimage calls dtc to create .itb image and assures that
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missing properties are added
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- .itb (new uImage) is uploaded onto the target and used therein
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d) Unique identifiers
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To identify FIT sub-nodes representing images, hashes, configurations (which
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are defined in the following sections), the "unit name" of the given sub-node
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is used as it's identifier as it assures uniqueness without additional
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checking required.
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3) Root node properties
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-----------------------
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Root node of the uImage Tree should have the following layout:
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/ o image-tree
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|- description = "image description"
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|- timestamp = <12399321>
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|- #address-cells = <1>
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o images
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| |
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| o img@1 {...}
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| o img@2 {...}
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| ...
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o configurations
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|- default = "cfg@1"
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o cfg@1 {...}
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o cfg@2 {...}
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...
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Optional property:
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- description : Textual description of the uImage
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Mandatory property:
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- timestamp : Last image modification time being counted in seconds since
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1970-01-01 00:00:00 - to be automatically calculated by mkimage tool.
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Conditionally mandatory property:
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- #address-cells : Number of 32bit cells required to represent entry and
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load addresses supplied within sub-image nodes. May be omitted when no
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entry or load addresses are used.
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Mandatory node:
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- images : This node contains a set of sub-nodes, each of them representing
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single component sub-image (like kernel, ramdisk, etc.). At least one
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sub-image is required.
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Optional node:
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- configurations : Contains a set of available configuration nodes and
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defines a default configuration.
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4) '/images' node
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-----------------
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This node is a container node for component sub-image nodes. Each sub-node of
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the '/images' node should have the following layout:
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o image@1
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|- description = "component sub-image description"
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|- data = /incbin/("path/to/data/file.bin")
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|- type = "sub-image type name"
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|- arch = "ARCH name"
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|- os = "OS name"
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|- compression = "compression name"
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|- load = <00000000>
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|- entry = <00000000>
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o hash@1 {...}
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o hash@2 {...}
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...
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Mandatory properties:
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- description : Textual description of the component sub-image
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- type : Name of component sub-image type, supported types are:
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"standalone", "kernel", "ramdisk", "firmware", "script", "filesystem",
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"fdt".
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- data : Path to the external file which contains this node's binary data.
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- compression : Compression used by included data. Supported compressions
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are "gzip" and "bzip2". If no compression is used compression property
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should be set to "none".
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Conditionally mandatory property:
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- os : OS name, mandatory for type="kernel", valid OS names are: "openbsd",
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"netbsd", "freebsd", "4_4bsd", "linux", "svr4", "esix", "solaris", "irix",
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"sco", "dell", "ncr", "lynxos", "vxworks", "psos", "qnx", "u_boot",
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"rtems", "unity", "integrity".
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- arch : Architecture name, mandatory for types: "standalone", "kernel",
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"firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha",
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"arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc",
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"sparc64", "m68k", "nios", "microblaze", "nios2", "blackfin", "avr32",
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"st200".
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- entry : entry point address, address size is determined by
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'#address-cells' property of the root node. Mandatory for for types:
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"standalone" and "kernel".
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- load : load address, address size is determined by '#address-cells'
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property of the root node. Mandatory for types: "standalone" and "kernel".
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Optional nodes:
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- hash@1 : Each hash sub-node represents separate hash or checksum
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calculated for node's data according to specified algorithm.
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5) Hash nodes
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-------------
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o hash@1
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|- algo = "hash or checksum algorithm name"
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|- value = [hash or checksum value]
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Mandatory properties:
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- algo : Algorithm name, supported are "crc32", "md5" and "sha1".
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- value : Actual checksum or hash value, correspondingly 4, 16 or 20 bytes
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long.
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6) '/configurations' node
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-------------------------
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The 'configurations' node is optional. If present, it allows to create a
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convenient, labeled boot configurations, which combine together kernel images
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with their ramdisks and fdt blobs.
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The 'configurations' node has has the following structure:
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o configurations
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|- default = "default configuration sub-node unit name"
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o config@1 {...}
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o config@2 {...}
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...
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Optional property:
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- default : Selects one of the configuration sub-nodes as a default
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configuration.
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Mandatory nodes:
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- configuration-sub-node-unit-name : At least one of the configuration
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sub-nodes is required.
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7) Configuration nodes
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----------------------
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Each configuration has the following structure:
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o config@1
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|- description = "configuration description"
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|- kernel = "kernel sub-node unit name"
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|- ramdisk = "ramdisk sub-node unit name"
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|- fdt = "fdt sub-node unit-name"
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Mandatory properties:
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- description : Textual configuration description.
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- kernel : Unit name of the corresponding kernel image (image sub-node of a
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"kernel" type).
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Optional properties:
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- ramdisk : Unit name of the corresponding ramdisk image (component image
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node of a "ramdisk" type).
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- fdt : Unit name of the corresponding fdt blob (component image node of a
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"fdt type").
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The FDT blob is required to properly boot FDT based kernel, so the minimal
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configuration for 2.6 FDT kernel is (kernel, fdt) pair.
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Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases
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'struct bd_info' must be passed instead of FDT blob, thus fdt property *must
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not* be specified in a configuration node.
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8) Examples
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-----------
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Please see doc/uImage.FIT/*.its for actual image source files.
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