S3C6410 uboot re-engineering (5) Setting up the stack and jumping to the C entry

Get straight to the point

1. Set up the stack

1 skip_hw_init:

2 /* Set up the stack */

3 stack_setup:

4 ldr r0, =CONFIG_SYS_UBOOT_BASE /* base of copy in DRAM */

//0x57e0_0000

5 sub r0, r0, #CONFIG_SYS_MALLOC_LEN /* malloc area */

//#define CONFIG_SYS_MALLOC_LEN (CONFIG_ENV_SIZE + 1024 * 1024)

//#define CONFIG_ENV_SIZE 0x4000

// Subtract the size of the environment variable storage area

6 sub r0, r0, #CONFIG_SYS_GBL_DATA_SIZE /* bdinfo */

//#define CONFIG_SYS_GBL_DATA_SIZE 128

// Subtract the size of the global variable storage area

7 sub sp, r0, #12 /* leave 3 words for abort-stack */

//Leave 12 bytes (3 words) of stack space

8

I personally do not trust this code, because I have also referred to the code of s3c-uboot1.1.6.

In the code of s3c-uboot1.1.6, #ifdef considers more comprehensive and more logical basis.

Therefore, this time we only analyze and produce a set of codes that can successfully run various basic functions, but in later practical use, this set of codes will not be used as long-term support code to avoid encountering unknown bugs.

2. Clear the BSS (Block Started by Symbol) segment

9 clear_bss:

10 ldr r0, _bss_start /* find start of bss segment */

11 ldr r1, _bss_end /* stop here */

12 mov r2, #0 /* clear */

//The comments are very clear... I won't explain them anymore

13

14 clbss_l:

15 str r2, [r0] /* clear loop... */

16 add r0, r0, #4 // loop to clear bss

17 cmp r0, r1

18 ble clbss_l

19

20 #ifndef CONFIG_NAND_SPL

21 ldr pc, _start_armboot // C entry function, selected after the IRQ interrupt processing code analysis

twenty two

23 _start_armboot:

24.word start_armboot

25 #else

26 b nand_boot

27 /* .word nand_boot*/

28 #endif

At this point, the analysis of the assembly interface code is complete, and the next step is the analysis of start_armboot in C language.

To summarize the structure in start.S, I personally think that the original code structure is clearer.

In uboot2010, the code structure tends to place several addressing operations in start.S, and other operations in lowlevel_init.

However, uboot1.1.6 pays more attention to the use of #ifdef, which separates more setting items.

Personally, I think 2010 has better logic and 1.1.6 is easier to debug.