Start of u-boot S analysis (IV)

• Next next to u-boot And start.S analysis （ 3、 ... and ） The final code analysis

Set the stack again

skip_hw_init:
	/* Set up the stack */
stack_setup:
#if defined(CONFIG_MEMORY_UPPER_CODE)
	ldr	sp, =(CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0x1000)
#else
	ldr	r0, _TEXT_BASE		/* upper 128 KiB: relocated uboot */
	sub	r0, r0, #CFG_MALLOC_LEN	/* malloc area */
	sub	r0, r0, #CFG_GBL_DATA_SIZE /* bdinfo */
#if defined(CONFIG_USE_IRQ)
	sub	r0, r0, #(CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ)
#endif
	sub	sp, r0, #12		/* leave 3 words for abort-stack */
#endif

• Through query, we can know , We have defined CONFIG_MEMORY_UPPER_CODE Of , So the stack pointer sp Set to CFG_UBOOT_BASE + CFG_UBOOT_SIZE - 0x1000, That is to say 0xc3e00000+2x1024x1024-0x1000=0xC3FFF000, The corresponding real address is 0x33fff000
• It means in the uboot Add 2M Re reduction 4K The place of , because ARM It's full minus stack , So from this position down about 2M Is the use space of the stack

clear BSS paragraph

clear_bss:
	ldr	r0, _bss_start		/* find start of bss segment */
	ldr	r1, _bss_end		/* stop here */
	mov r2, #0x00000000		/* clear */

• _bss_start and _bss_end From linker script （ Omit a layer of definition in the middle ）

. = ALIGN(4);
__bss_start = .;
.bss : {
     *(.bss) }
_end = .;

start-up start_armboot

clbss_l:
	str	r2, [r0]		/* clear loop... */
	add	r0, r0, #4
	cmp	r0, r1
	ble	clbss_l
	
	ldr	pc, _start_armboot

_start_armboot:
	.word start_armboot

• thus , The first stage analysis is completed
• start_armboot Function in uboot/lib_arm/board.c in , It's a C Language functions
• Finally through lpr The far jump instruction executes the function start_armboot
• Far jump means that the loaded address has nothing to do with the current running address , And he Link address of

1. stay u-boot And start.S analysis （ One ） in , Set the stack to the internal SRAM in , Perhaps only 8K size ,uboot Execute part of the code here
2. stay u-boot And start.S analysis （ 3、 ... and ） in , Reset the stack to the one that has been initialized DDR in
3. Finally, re plan DDR Use , Reset stack , Jump to... When setup is complete DDR Execute the second stage in .