Embedded startup process

A term is used to explain
ROM Integrated into the SOC Internal read only memory
BootROM Stored in Rom The first section of the running program
BL：BootLoader by OS The operation of the hardware driver （PC It's called BIOS）
SPL：Second Program Loader Compare with BootRom The second section of the running program
DDR： Commonly known memory
SRAM： Integrated into the SOC Small internal memory
U-Boot： Open source BootLoader Program GPL v2

1. CPU Of PC Point to BootROM
2. BootROM（BL0）：1~16KB
   Local initialization Flash,Flash It may work at a low rate
   check SPL
   take SPL Copy the code to SRAM
   Control to SPL（ Jump to SPL First line of code for ）
3. SPL（BL1）： Less than 128KB
   initialization DDR、Flash
   check U-Boot
   take U-Boot copy to DDR
   Control to U-Boot（ Jump to U-Boot First line of code for ）
4. U-Boot（BL2）： Less than 2M
   initialization Flash
   take OS copy to DDR
   Control to OS（ Jump to OS First line of code for ）
5. OS： It can be very big , There is no limit to
   Drive of all equipment
   memory management 、 file system 、 Process management …
   start-up shell, Automatically run the agreed script
   Waiting for user input instructions

Reference resources