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diff --git a/doc/uImage.FIT/source_file_format.txt b/doc/uImage.FIT/source_file_format.txt new file mode 100644 index 0000000..1d75458 --- /dev/null +++ b/doc/uImage.FIT/source_file_format.txt @@ -0,0 +1,262 @@ +U-boot new uImage source file format (bindings definition) +========================================================== + +Author: Marian Balakowicz <m8@semihalf.com> + +1) Introduction +--------------- + +Evolution of the 2.6 Linux kernel for embedded PowerPC systems introduced new +booting method which requires that hardware description is available to the +kernel in the form of Flattened Device Tree. + +Booting with a Flattened Device Tree is much more flexible and is intended to +replace direct passing of 'struct bd_info' which was used to boot pre-FDT +kernels. + +However, U-boot needs to support both techniques to provide backward +compatibility for platforms which are not FDT ready. Number of elements +playing role in the booting process has increased and now includes the FDT +blob. Kernel image, FDT blob and possibly ramdisk image - all must be placed +in the system memory and passed to bootm as a arguments. Some of them may be +missing: FDT is not present for legacy platforms, ramdisk is always optional. +Additionally, old uImage format has been extended to support multi sub-images +but the support is limited by simple format of the legacy uImage structure. +Single binary header 'struct image_header' is not flexible enough to cover all +possible scenarios. + +All those factors combined clearly show that there is a need for new, more +flexible, multi component uImage format. + + +2) New uImage format assumptions +-------------------------------- + +a) Implementation + +Libfdt has been selected for the new uImage format implementation as (1) it +provides needed functionality, (2) is actively maintained and developed and +(3) increases code reuse as it is already part of the U-boot source tree. + +b) Terminology + +This document defines new uImage structure by providing FDT bindings for new +uImage internals. Bindings are defined from U-boot perspective, i.e. describe +final form of the uImage at the moment when it reaches U-boot. User +perspective may be simpler, as some of the properties (like timestamps and +hashes) will need to be filled in automatically by the U-boot mkimage tool. + +To avoid confusion with the kernel FDT the following naming convention is +proposed for the new uImage format related terms: + +FIT - Flattened uImage Tree + +FIT is formally a flattened device tree (in the libfdt meaning), which +conforms to bindings defined in this document. + +.its - image tree source +.itb - image tree blob + +c) Image building procedure + +The following picture shows how the new uImage is prepared. Input consists of +image source file (.its) and a set of data files. Image is created with the +help of standard U-boot mkimage tool which in turn uses dtc (device tree +compiler) to produce image tree blob (.itb). Resulting .itb file is is the +actual binary of a new uImage. + + +tqm5200.its ++ +vmlinux.bin.gz mkimage + dtc xfer to target +eldk-4.2-ramdisk --------------> tqm5200.itb --------------> bootm +tqm5200.dtb /|\ +... | + 'new uImage' + + - create .its file, automatically filled-in properties are omitted + - call mkimage tool on a .its file + - mkimage calls dtc to create .itb image and assures that + missing properties are added + - .itb (new uImage) is uploaded onto the target and used therein + + +d) Unique identifiers + +To identify FIT sub-nodes representing images, hashes, configurations (which +are defined in the following sections), the "unit name" of the given sub-node +is used as it's identifier as it assures uniqueness without additional +checking required. + + +3) Root node properties +----------------------- + +Root node of the uImage Tree should have the following layout: + +/ o image-tree + |- description = "image description" + |- timestamp = <12399321> + |- #address-cells = <1> + | + o images + | | + | o img@1 {...} + | o img@2 {...} + | ... + | + o configurations + |- default = "cfg@1" + | + o cfg@1 {...} + o cfg@2 {...} + ... + + + Optional property: + - description : Textual description of the uImage + + Mandatory property: + - timestamp : Last image modification time being counted in seconds since + 1970-01-01 00:00:00 - to be automatically calculated by mkimage tool. + + Conditionally mandatory property: + - #address-cells : Number of 32bit cells required to represent entry and + load addresses supplied within sub-image nodes. May be omitted when no + entry or load addresses are used. + + Mandatory node: + - images : This node contains a set of sub-nodes, each of them representing + single component sub-image (like kernel, ramdisk, etc.). At least one + sub-image is required. + + Optional node: + - configurations : Contains a set of available configuration nodes and + defines a default configuration. + + +4) '/images' node +----------------- + +This node is a container node for component sub-image nodes. Each sub-node of +the '/images' node should have the following layout: + + o image@1 + |- description = "component sub-image description" + |- data = /incbin/("path/to/data/file.bin") + |- type = "sub-image type name" + |- arch = "ARCH name" + |- os = "OS name" + |- compression = "compression name" + |- load = <00000000> + |- entry = <00000000> + | + o hash@1 {...} + o hash@2 {...} + ... + + Mandatory properties: + - description : Textual description of the component sub-image + - type : Name of component sub-image type, supported types are: + "standalone", "kernel", "ramdisk", "firmware", "script", "filesystem", + "fdt". + - data : Path to the external file which contains this node's binary data. + - compression : Compression used by included data. Supported compressions + are "gzip" and "bzip2". If no compression is used compression property + should be set to "none". + + Conditionally mandatory property: + - os : OS name, mandatory for type="kernel", valid OS names are: "openbsd", + "netbsd", "freebsd", "4_4bsd", "linux", "svr4", "esix", "solaris", "irix", + "sco", "dell", "ncr", "lynxos", "vxworks", "psos", "qnx", "u_boot", + "rtems", "artos", "unity". + - arch : Architecture name, mandatory for types: "standalone", "kernel", + "firmware", "ramdisk" and "fdt". Valid architecture names are: "alpha", + "arm", "i386", "ia64", "mips", "mips64", "ppc", "s390", "sh", "sparc", + "sparc64", "m68k", "nios", "microblaze", "nios2", "blackfin", "avr32", + "st200". + - entry : entry point address, address size is determined by + '#address-cells' property of the root node. Mandatory for for types: + "standalone" and "kernel". + - load : load address, address size is determined by '#address-cells' + property of the root node. Mandatory for types: "standalone" and "kernel". + + Optional nodes: + - hash@1 : Each hash sub-node represents separate hash or checksum + calculated for node's data according to specified algorithm. + + +5) Hash nodes +------------- + +o hash@1 + |- algo = "hash or checksum algorithm name" + |- value = [hash or checksum value] + + Mandatory properties: + - algo : Algorithm name, supported are "crc32", "md5" and "sha1". + - value : Actual checksum or hash value, correspondingly 4, 16 or 20 bytes + long. + + +6) '/configurations' node +------------------------- + +The 'configurations' node is optional. If present, it allows to create a +convenient, labeled boot configurations, which combine together kernel images +with their ramdisks and fdt blobs. + +The 'configurations' node has has the following structure: + +o configurations + |- default = "default configuration sub-node unit name" + | + o config@1 {...} + o config@2 {...} + ... + + + Optional property: + - default : Selects one of the configuration sub-nodes as a default + configuration. + + Mandatory nodes: + - configuration-sub-node-unit-name : At least one of the configuration + sub-nodes is required. + + +7) Configuration nodes +---------------------- + +Each configuration has the following structure: + +o config@1 + |- description = "configuration description" + |- kernel = "kernel sub-node unit name" + |- ramdisk = "ramdisk sub-node unit name" + |- fdt = "fdt sub-node unit-name" + + + Mandatory properties: + - description : Textual configuration description. + - kernel : Unit name of the corresponding kernel image (image sub-node of a + "kernel" type). + + Optional properties: + - ramdisk : Unit name of the corresponding ramdisk image (component image + node of a "ramdisk" type). + - fdt : Unit name of the corresponding fdt blob (component image node of a + "fdt type"). + +The FDT blob is required to properly boot FDT based kernel, so the minimal +configuration for 2.6 FDT kernel is (kernel, fdt) pair. + +Older, 2.4 kernel and 2.6 non-FDT kernel do not use FDT blob, in such cases +'struct bd_info' must be passed instead of FDT blob, thus fdt property *must +not* be specified in a configuration node. + + +8) Examples +----------- + +Please see doc/uImage.FIT/*.its for actual image source files. |