This is an unnamed and undocumented partition table format implemented by the bootloader and kernel that Amlogic provides for their Linux SoCs (Meson series at least, and probably others). They appear to use this rather than GPT, the industry standard, because their BootROM loads and executes the next stage loader from offset 512 (0x200) on the eMMC, which is exactly where the GPT header would have to start. So instead of changing their BootROM, Amlogic devised this partition table, which lives at an offset of 36MiB (0x240_0000) on the eMMC and so doesn't conflict. This parser expects as input just the partition table from that offset. The maximum number of partitions in a table is 32, which corresponds to a maximum table size of 1304 bytes (0x518).
This page hosts a formal specification of Amlogic proprietary eMMC partition table using Kaitai Struct. This specification can be automatically translated into a variety of programming languages to get a parsing library.
All parsing code for JavaScript generated by Kaitai Struct depends on the JavaScript runtime library. You have to install it before you can parse data.
The JavaScript runtime library is available at npm:
npm install kaitai-structSee the usage examples in the JavaScript notes.
Parse structure from an ArrayBuffer:
var arrayBuffer = ...;
var data = new AmlogicEmmcPartitions(new KaitaiStream(arrayBuffer));
After that, one can get various attributes from the structure by accessing fields or properties like:
data.checksum // => To calculate this, treat the first (and only the first) partition
descriptor in the table below as an array of unsigned little-endian
32-bit integers. Sum all those integers mod 2^32, then multiply the
result by the total number of partitions, also mod 2^32. Amlogic
likely meant to include all the partition descriptors in the sum,
but their code as written instead repeatedly loops over the first
one, once for each partition in the table.
// This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild
(function (root, factory) {
if (typeof define === 'function' && define.amd) {
define(['kaitai-struct/KaitaiStream'], factory);
} else if (typeof module === 'object' && module.exports) {
module.exports = factory(require('kaitai-struct/KaitaiStream'));
} else {
root.AmlogicEmmcPartitions = factory(root.KaitaiStream);
}
}(typeof self !== 'undefined' ? self : this, function (KaitaiStream) {
/**
* This is an unnamed and undocumented partition table format implemented by
* the bootloader and kernel that Amlogic provides for their Linux SoCs (Meson
* series at least, and probably others). They appear to use this rather than GPT,
* the industry standard, because their BootROM loads and executes the next stage
* loader from offset 512 (0x200) on the eMMC, which is exactly where the GPT
* header would have to start. So instead of changing their BootROM, Amlogic
* devised this partition table, which lives at an offset of 36MiB (0x240_0000)
* on the eMMC and so doesn't conflict. This parser expects as input just the
* partition table from that offset. The maximum number of partitions in a table
* is 32, which corresponds to a maximum table size of 1304 bytes (0x518).
* @see {@link http://aml-code.amlogic.com/kernel/common.git/tree/include/linux/mmc/emmc_partitions.h?id=18a4a87072ababf76ea08c8539e939b5b8a440ef|Source}
* @see {@link http://aml-code.amlogic.com/kernel/common.git/tree/drivers/amlogic/mmc/emmc_partitions.c?id=18a4a87072ababf76ea08c8539e939b5b8a440ef|Source}
*/
var AmlogicEmmcPartitions = (function() {
function AmlogicEmmcPartitions(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
AmlogicEmmcPartitions.prototype._read = function() {
this.magic = this._io.readBytes(4);
if (!((KaitaiStream.byteArrayCompare(this.magic, [77, 80, 84, 0]) == 0))) {
throw new KaitaiStream.ValidationNotEqualError([77, 80, 84, 0], this.magic, this._io, "/seq/0");
}
this.version = KaitaiStream.bytesToStr(KaitaiStream.bytesTerminate(this._io.readBytes(12), 0, false), "UTF-8");
this.numPartitions = this._io.readS4le();
if (!(this.numPartitions >= 1)) {
throw new KaitaiStream.ValidationLessThanError(1, this.numPartitions, this._io, "/seq/2");
}
if (!(this.numPartitions <= 32)) {
throw new KaitaiStream.ValidationGreaterThanError(32, this.numPartitions, this._io, "/seq/2");
}
this.checksum = this._io.readU4le();
this.partitions = [];
for (var i = 0; i < this.numPartitions; i++) {
this.partitions.push(new Partition(this._io, this, this._root));
}
}
var Partition = AmlogicEmmcPartitions.Partition = (function() {
function Partition(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
Partition.prototype._read = function() {
this.name = KaitaiStream.bytesToStr(KaitaiStream.bytesTerminate(this._io.readBytes(16), 0, false), "UTF-8");
this.size = this._io.readU8le();
this.offset = this._io.readU8le();
this._raw_flags = this._io.readBytes(4);
var _io__raw_flags = new KaitaiStream(this._raw_flags);
this.flags = new PartFlags(_io__raw_flags, this, this._root);
this.padding = this._io.readBytes(4);
}
var PartFlags = Partition.PartFlags = (function() {
function PartFlags(_io, _parent, _root) {
this._io = _io;
this._parent = _parent;
this._root = _root || this;
this._read();
}
PartFlags.prototype._read = function() {
this.isCode = this._io.readBitsIntLe(1) != 0;
this.isCache = this._io.readBitsIntLe(1) != 0;
this.isData = this._io.readBitsIntLe(1) != 0;
}
return PartFlags;
})();
/**
* The start of the partition relative to the start of the eMMC, in bytes
*/
return Partition;
})();
/**
* To calculate this, treat the first (and only the first) partition
* descriptor in the table below as an array of unsigned little-endian
* 32-bit integers. Sum all those integers mod 2^32, then multiply the
* result by the total number of partitions, also mod 2^32. Amlogic
* likely meant to include all the partition descriptors in the sum,
* but their code as written instead repeatedly loops over the first
* one, once for each partition in the table.
*/
return AmlogicEmmcPartitions;
})();
return AmlogicEmmcPartitions;
}));