[Linux transplant] ——2. Transplanting u-boot-2012.04.01 refers to analyzing the boot process

1. Transplanting u-boot-2012.04.01 refers to analyzing the boot process

a. Get the source code:

Download u-boot-2012.04.01.tar.bz2 from ftp://ftp.denx.de/pub/u-boot/ and download the cross-compilation chain arm-linux-gcc-4.3.2.tar.bz2.

b. Unzip u-boot-2012.04.01.tar.bz2 to your PC and create a Source Insight project.

Put u-boot-2012.04.01.tar.bz2 on Ubuntu and decompress it, and install arm-linux-gcc-4.3.2.tar.bz2 at the same time.

c. After building the Source Insight project, add the corresponding files to analyze the startup process of u-boot-2012.04.01:

According to the linking process, open start.S for code analysis:

1. Set the CPU to management mode set the cpu to SVC32 mode

2. Turn off the watchdog

3. Mask all IRQs by setting all bits in the INTMR

4. Set the frequency division clock ratio

5. Set up the memory control controller (CPU bottom layer initialization)

6. Set up the stack and call the C function board_init_f

7. Call each function in the function array init_sequence

7.1 board_early_init_f: Set system clock, set GPIO

... ...

8. Relocation code

8.1 Copy code from NOR FLASH to SDRAM

8.2 The link address of the program is 0. When accessing global variables, static variables, and calling functions, the "address compiled based on address 0" is used.

      Now copy the program to SDRAM

      The code needs to be modified to change the "address compiled based on address 0" to the new address

8.3 Some addresses in the program cannot be determined at link time and can only be determined before running: fixabs

9. clear_bss

10. Calling C function board_init_r: Stage 2 code