ARM-Linux boot method

      ARM-Linux uses ARM chips, which have high execution efficiency, powerful functions, and relatively rich peripherals. It is a powerful computer system and needs to run an operating system, so its startup method is quite different from that of a single-chip microcomputer, but it is basically the same as the startup method of a home computer. Its startup generally includes BIOS, bootloader, kernel startup, application startup and other stages.

(a) Start BIOS

      BIOS is the corresponding startup information set by the device manufacturer (chip or circuit board manufacturer). After the device is powered on, it will read the corresponding hardware device information, initialize the hardware device, and then jump to the location of the bootloader (this location is a fixed location set by BIOS). (According to my personal understanding, the startup of BIOS is similar to the startup of the microcontroller. The corresponding hardware debugger is required to write the firmware and store it in a certain flash space. After the device is powered on, the instructions in the flash space are read to start the BIOS program.)

(b) Start the bootloader

      This part already belongs to the embedded Linux software development part. You can modify the code to customize the corresponding bootloader program. The bootloader is usually downloaded by directly reading and writing the SD card. That is, write and customize the corresponding bootloader, compile and generate the bootloader image file, and then use the tool (special or general) to download it to the MBR area of ​​the SD card (usually the first sector of the storage area). At this time, you need to set it in the BIOS, or through the hardware circuit setting of the circuit board, select the loading location of the bootloader; if the BIOS is set to start from the SD card, after the BIOS initialization is completed, it will jump to the location of the SD card to execute the bootloader, thereby realizing the startup of the bootloader.

      The main function of the Bootloader is to initialize the necessary hardware devices, create some information required by the kernel and pass this information to the kernel through relevant mechanisms, so as to bring the system's hardware and software environment to a suitable state, and finally call the operating system kernel to truly play the role of booting and loading the kernel.

(c) Start the kernel

      After the bootloader completes initialization and other related work, it will call the kernel startup program. This is the start of the actual operating system related content, including the corresponding hardware configuration, task management, resource management and other kernel program startup.

(d) Start the application

      After the operating system kernel is started, you can start the required applications to complete the actual business operations.