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Uboot can achieve what functions, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

The Origin and Development of Uboot

1. The origin of Uboot?

Here we have a brief understanding of the origin of Uboot. Uboot started as a project initiated by a German god, which was later transferred to SourceFore.net by Wolfgang Denk, but the name of the project that begins with a number is not allowed on SourceForge.net, so it is renamed PPCBoot. PPCBoot was first released publicly on July 19, 2000; in fact, Uboot evolved from FADSROM, 8xxROM, and PPCBOOT. During this period, it has been used by many people, and even by many Soc (abbreviation of System on Chip, called chip-level system, also known as system-on-chip, which means that it is a product, an integrated circuit with a specific target, which contains a complete system and embedded software. Vendor support, which further promotes the widespread use of Uboot. Finally, after years of development, Uboot has become the bootloader (bootstrap) standard in the industry, and now most embedded devices will use Uboot as bootloader by default.

2. The version number of Uboot:

1. The early version of Uboot is similar to this: Uboot 1.3.4 (that is, the older version), but the later version number is not named in this way, but in the form of Uboot-2010.06. So when we see the version numbers of various Uboot, we need to be able to identify them. Below we can download the source code of Uboot from this place. It is not recommended to download the source code of Uboot from the official website. It is too slow. Here I provide a download website: https://ftp.denx.de/pub/u-boot/ Here are the Uboot source code version numbers of various versions. You can download and learn if you need to. At the same time, note that the general download suffix does not have the version number of "rc", because the version with "rc" is unstable, that is, the test version:

2. In fact, the core of Uboot is almost unchanged, although there are many new Uboot version numbers, only that more and more embedded development boards are supported by the newer version, so generally speaking, there is no difference between the new version and the old version of Uboot core. In fact, sometimes when we look at the Linux source code, the opposite of the old version may be more classic and easy to get started.

Third, the understanding of Uboot portability:

1. Uboot is universal bootloader (universal bootstrap), which means it can be used everywhere. For example, Uboot can support boot boot of embedded Linux system, and it also supports NetBSD, VxWorks, android and other embedded operating systems, and it can also support MIPS, x86 and other commonly used series of processors. Generally speaking, Uboot has the most complete and rich support for PowerPC processors and the most perfect support for Linux systems. So overall, Uboot is very portable.

What are the functions of Uboot

First, you can turn it on and start it directly:

General Soc supports a variety of startup methods, such as SD card startup, NorFlash startup, NandFlash startup and so on, so uboot; must be designed according to the specific SoC startup design and Uboot must make code-level changes and porting corresponding to the hardware in order to ensure that it can be started from the corresponding boot media; this piece is specifically dealt with in the start .s file of the first stage of Uboot.

Second, it can boot the operating system kernel and pass parameters to the kernel:

The ultimate goal of Uboot is to start the kernel. When the Linux kernel is designed to be able to pass parameters, that is to say, we can prepare some startup parameters for the Linux kernel in Uboot and put them in a specific location in memory, and then pass them to the Linux kernel. After starting, the Linux kernel will go to this specific location to get the parameters passed to it by Uboot, and then parse these parameters in the Linux kernel. These parameters will be used to guide the startup process of the Linux kernel.

Third, be able to provide system deployment functions:

Uboot must be able to burn and download the entire system (including images of Uboot, Kernel, rootfs, etc.) on Flash with the help of us.

Fourth, be able to manage hardware at Soc level and board level:

Part of the hardware control is realized in Uboot (part of the hardware is initialized in Uboot). This is because Uboot has to make the hardware work in order to accomplish some tasks. For example, in order to be able to brush the machine, Uboot must be able to drive iNand (iNAND is a memory chip developed by SanDisk). The SoC level (such as serial port) is the SoC internal peripherals, and the board level is the hardware on the SoC external development board (such as network card, iNand).

5. Summary:

In short, Uboot is to be able to boot the kernel and get our operating system running.

Life cycle of Uboot

The life cycle of uboot refers to when the uboot starts to run and when it ends.

Uboot is essentially a bare metal program (not an operating system). Once uboot starts, SoC simply runs uboot (meaning that it is impossible for uboot to run other programs at the same time), and once uboot finishes running, it can't go back to uboot (so uboot itself died after uboot started the kernel, and you have to restart the system if you want to see the uboot interface again. Restart is not a resurrection of the previous uboot, restart is just another life of uboot).

Entrances and exits of uboot. The entrance to uboot is to boot automatically, and the only exit to uboot is to boot the kernel. Uboot can also perform many other tasks (such as the burning system), but after other tasks have been executed, you can go back to the uboot command line and continue to execute the uboot command, while the boot kernel command will not come back once executed.

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