U-Boot transplantation (8) u-boot process

u-boot startup process:

　　From the file level, the main processes are in two files: cpu/arm920t/start.s, lib_arm/board.c,　

　　1)start.s　

   The boot code executed in flash, which is stage1 in bootloader, is responsible for initializing the hardware environment, loading u-boot from flash into RAM, and then jumping to start_armboot in lib_arm/board.c for execution.

1.1.6u-boot start.s process:

Hardware environment initialization:

   　　Enter svc mode; turn off watch dog; shield all IRQ masks; set clock frequencies FCLK, HCLK, PCLK; clear I/D cache; disable MMU and CACHE; configure memory control;

reset:

   　　If the current code is not at the address specified by the connection (0x3f000000 for smdk2410), u-boot needs to be copied from the current location to the RAM specified location;

            Establish a stack. The stack must be initialized before entering the C function.

Clear the .bss area.

Jump to the start_armboot function for execution. (lib_arm/board.c)

2)lib_arm/board.c:

  　start_armboot is the first C language function executed by U-Boot. It completes the system initialization work, enters the main loop, and processes the commands entered by the user. Here is only a brief list of the main executed function flows:

   void start_armboot (void)

   {

       //The global data variable pointer gd occupies r8.

          DECLARE_GLOBAL_DATA_PTR;

          /* Arrange space for the global data variable gd*/

          gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));

          memset ((void*)gd, 0, sizeof (gd_t));

          /* Arrange space for the board data variable gd->bd*/

          gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));

          memset (gd->bd, 0, sizeof (bd_t));

          monitor_flash_len = _bss_start - _armboot_start;//Get the length of u-boot.

          /* Execute the initialization functions in the init_sequence array sequentially*/

          for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {

                 if ((*init_fnc_ptr)() != 0) {

                         hang();

                 }

          }

          /*Configure available Flash */

          size = flash_init ();

       　…

          /*Initialize heap space*/

          mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);

          /* Relocate environment variables, */

         env_relocate ();

          /* Get the IP address from the environment variable */

          gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");

          /* Ethernet interface MAC address */

          …

          devices_init (); /* device initialization*/

          jumptable_init (); //Jump table initialization

          console_init_r (); /* Completely initialize the console device*/

          enable_interrupts (); /* Enable interrupt processing*/

          /* Initialize through environment variables */

          if ((s = getenv ("loadaddr")) != NULL) {

                  load_addr = simple_strtoul (s, NULL, 16);

          }

          /* main_loop() loop is executed continuously*/

          for (;;) {

                  main_loop (); /* The main loop function processes and executes user commands-- common/main.c */

          }

   }

Initialization function sequence init_sequence[]

  The init_sequence[] array stores basic initialization function pointers. The names of these functions and the program files that implement them are in the comments below.

  init_fnc_t *init_sequence[] = {

         cpu_init, /* Basic processor related configuration--cpu/arm920t/cpu.c */

         board_init, /* Basic board-level configuration-- board/smdk2410/smdk2410.c */

         interrupt_init, /* Initialization exception handling--cpu/arm920t/s3c24x0/interrupt.c */

         env_init, /* Initialize environment variables--common/env_flash.c */

         init_baudrate, /* Initialize baud rate setting-- lib_arm/board.c */

         serial_init, /* Serial communication settings--cpu/arm920t/s3c24x0/serial.c */

         console_init_f, /* Console initialization phase 1 -- common/console.c */

         display_banner, /* print u-boot information-- lib_arm/board.c */

         dram_init, /* Configure available RAM -- board/smdk2410/smdk2410.c */

         display_dram_config, /* Display RAM configuration size-- lib_arm/board.c */

         NULL,

  };

The execution of the entire u-boot enters an infinite loop of waiting for the user to enter a command, parsing and executing the command.