［原创］Flow of U-Boot Starup

• Lowlevel initialization: Implements basic hardware initialization, including the clock setting and SDRAM initialization, and so on;
• Relocate: Copy U-Boot from Flash to SDRAM, including the code and data section (.text, .rodata, .data and .got );
• Setup stack: Establish the environment of C language;
• Clean bss: Clean the bss section;