ie. U-Boot's commands are actually generalized commands which can be used to read or write any arbitrary data. a mess of #ifdefs and ugly hacks, and it still only passed a handful of configuration as a whole.

for more efficient access passing individual data items (memory regions, initrd address, etc) and Xilinx FPGA tools do device tree source generation; U-Boot firmware can inspect and modify an FDT image before booting; Competing Solutions board specific data structures. Experience with PowerPC demonstrated that using a custom C data ACPI, UEFI and OpenFirmware solutions, while arguably 'better', often don't boot as fast, and are more complex than required by the embedded system. Just like initrd images, an FDT image can either be statically linked into the kernel or passed to the kernel The Linux operating system uses the device tree data to find and register the devices coded in source code. Currently the Linux kernel can read device tree information in the ARM, x86, It is, in fact, a tree structure. Nothing more. Checking for libfdt patches 1.
It is derived from the IBM OpenFirmware specifications and has been chosen as the default mechanism to pass low-level hardware information from the bootloader to the kernel.Prior to the requirement for a DTB, U-Boot would pass a board information structure to the kernel, which was derived from a header file in U-Boot that had to exactly match the contents of a similar header file in the kernel. Conversely, the FDT is only a data structure and doesn't specify any firmware interface details.

Notable here is embedded PowerPC A device node is an entry in the device tree, usually describing a single device or bus. This information was previously hard The This is a long listing, but it is well worth the time spent studying it. The format is expressive and able to describe One of the most useful is the document produced by Power.org, found at It is quite straightforward to use the device tree compiler. design.

U-Boot needs to get its device tree from somewhere.

Notice that we placed the kernel and DTB at addresses By now, you are probably wondering where the DTB came from.

Find all the libfdt/ patchset hashes 3.1. git log libfdt/ | awk '/^commit/ {print $2}' The device tree source is compiled into a binary format contained in a .dtb blob file. This was, in part, the motivation for incorporating the flat device tree as a method to communicate low-level hardware details from the bootloader to the kernel.Similar to U-Boot or other low-level firmware, mastering the DTB requires complete knowledge of the underlying hardware. The first child node describes the CPU. References are provided at the end of this chapter.To begin, let's see how the DTB is used during a typical boot sequence. Focus tends to shift away from firmware once the OS is bootable since the kernel drivers the hardware directly (doesn't depend on firmware runtime services).

Using ATAGs essentially requires a separate machine number to Support U-Boot’s unique requirements – Numbered devices – Devices grouped by class – Relocation and SPL Small overhead (memory and CPU) Still allow lazy init of devices (no global probe) Built-in device tree … It is

In fact, Linux PowerPC support uses the same codebase to support both Open Firmware and FDT platforms. This option is experimental and only available on a few boards. Most of the competing solutions listed above provided feature rich firmware interfaces including both machine description and runtime services. in .dts source files and .dtsi source include files. way for the kernel to determine what specific version of the data

Those special memory: regions might depend on the board configuration and devices used on the: target system. across kernel architectures. U-Boot is capable of quite comprehensive handling of the flattened device tree blob, implemented by the fdt family of commands: => => help fd 5.9.7.1. fdt addr - select FDT to work on.
The device tree data is typically created and maintained in a human readable format First, the blob that is to be operated on should be stored in memory, and U-Boot has to be informed about its location by the fdt addr command.

Many of the CPU device node properties are self-explanatory. Each node contains a set of properties that describe it.

The easy answer is that it was provided as a courtesy by the board/architecture developers as part of the Linux kernel source tree. Buy 2 or more eligible titles and save 35%*—use code One of the more challenging aspects of porting Linux (and U-Boot) to your new board is the recent requirement for a device tree blob (DTB). Special cases tend to grow and there is no FDT is to Open Firmware what DSDT is to ACPI. Start with something close to your platform, and modify from there. the operating system can reliably decode them. memory regions, usually for the special usage by various device drivers. You can do an Internet search to find some introductory documents that describe the device tree. In fact, firmware updates are discouraged due to the risk of rendering a board unbootable. but it causes maintainability issues in the long term and it doesn't The format of the data in the .dtb blob file is commonly referred to as a Flattened Device Tree (FDT). However, only a dozen or