Transplant uboot-analyze uboot startup process (detailed explanation)

This section summarizes:

The uboot startup process is as follows:

1) Set CPU to management mode
2) Turn off watchdog
3) Turn off interrupt
4) Set clock frequency
5)
Turn off mmu, initialize each bank 6) Enter board_init_f() function (initialize timer, GPIO, serial port, etc., divide memory area )
7) Relocate and copy uboot, and then modify the uboot link address on SDRAM)
8) Clear bss
9) Jump to the board_init_r() function, the startup process ends
Reprinted from transplanted uboot-analyze uboot startup process (detailed explanation)