There is a lot of information on the start-up process of embedded Linux. There is only a brief introduction here, aiming at getting a quick understanding of the entire startup process.
The entire boot process can be attributed to the following points:
First, introduce each one:
ROM Code (solidified code in the chip), starting with the initial boot function, including initialization clock, on-chip RAM, related peripherals, read pin configuration information, etc.
U-Boot (Universal Boot Loader) initializes related hardware devices and boots the system to load a section of the kernel image.
Kernel, responsible for the management of memory, files, and peripherals, as well as process communication and scheduling;
File system, responsible for file management;
Applications are individual applications.
To illustrate the image, we compared the entire process to driving a car. We changed the above picture:
After the power is turned on, the CPU executes a hardened internal code (ROM Code), initializes related peripherals, and selects which storage device to read U-Boot (emmc, TF card...) according to the information of the external pin. Then, U-Boot is loaded into memory to run. After U-Boot has finished configuring related peripherals, Kernel is loaded into memory. At this point, Kernel is responsible for the remaining tasks.
Here the ROM Code is the first action performed after power-up, it is quite a boot-booting process; U-Boot, in addition to the initial peripherals, there is a very important point is to initialize the relevant memory space for the Kernel, prepare for its loading, In fact, this is equivalent to making the engine start, it is necessary to provide it with energy; with the engine no equipment, empty power can not do anything real, on the contrary, no engine to provide power, equipment can not move, here actually reveals Kernel and the file system are inextricably linked; when everything is ready, we can write and run application-related programs (drive) on it.
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