Start of u-boot_ Armboot analysis (I)

• Skip all undefined macro definitions
• This is a uboot Entry function of the second stage
• Function in lib_arm/board.c in

DECLARE_GLOBAL_DATA_PTR

#define DECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r8")

• Defines a register to be placed in r8 Global variable in , Name is gd, A type is a pointer to gd_t Pointer to type variable .
• gd_t stay include/asm-arm/global_data.h In the definition of , The contents are as follows

typedef	struct	global_data {
    
	bd_t		*bd;
	unsigned long	flags;
	unsigned long	baudrate;
	unsigned long	have_console;	/* serial_init() was called */
	unsigned long	reloc_off;	/* Relocation Offset */
	unsigned long	env_addr;	/* Address of Environment struct */
	unsigned long	env_valid;	/* Checksum of Environment valid? */
	unsigned long	fb_base;	/* base address of frame buffer */
#ifdef CONFIG_VFD
	unsigned char	vfd_type;	/* display type */
#endif
	void		**jt;		/* jump table */
} gd_t;

• These are some configuration files of the board .
• bd->bi_arch_number It is the machine code of the board
• bd->bi_boot_params It's for linux The address of the startup parameter of

Distribution of memory

#ifdef CONFIG_MEMORY_UPPER_CODE
	ulong gd_base;
	gd_base = CFG_UBOOT_BASE + CFG_UBOOT_SIZE - CFG_MALLOC_LEN - CFG_STACK_SIZE - sizeof(gd_t);
#ifdef CONFIG_USE_IRQ
	gd_base -= (CONFIG_STACKSIZE_IRQ+CONFIG_STACKSIZE_FIQ);
#endif //CONFIG_USE_IRQ
	gd = (gd_t*)gd_base;
#else //CONFIG_MEMORY_UPPER_CODE
	gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));
#endif //CONFIG_MEMORY_UPPER_CODE
	/* compiler optimization barrier needed for GCC >= 3.4 */
	__asm__ __volatile__("": : :"memory");

	memset ((void*)gd, 0, sizeof (gd_t));
	gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
	memset (gd->bd, 0, sizeof (bd_t));

• Only for the first time gd_base It works for us
• Variable gd_base Refers to gd stay DDR The starting address of memory allocation in
• gd_base = CFG_UBOOT_BASE + CFG_UBOOT_SIZE - CFG_MALLOC_LEN - CFG_STACK_SIZE - sizeof(gd_t) The end result is 0xc3e00000+(2x1024x1024) - 912*1024 - 512*1024 - 36 = 0xc3e9bfdc
• Direct will gd_base Assigned to a global variable gd
• gd->bd stay gd Down sizeof(bd_t) The location of
• combination uboot Start the first phase for the last time sp Pointer setting , The final memory structure is as follows
  

Hardware initialization

monitor_flash_len = _bss_start - _armboot_start;

for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
    
	if ((*init_fnc_ptr)() != 0) {
    
		hang ();
	}
}

• Is a global variable monitor_flash_len assignment
• init_fnc_ptr For the definition of init_fnc_t **init_fnc_ptr, and init_func_t For the definition of typedef int (init_fnc_t) (void); This shows that init_func_t Is a receive parameter void And the return value is int The function type of
• init_sequence A series of functions are defined in , The function of this code is to execute the initialization function , If any function returns a value other than 0, Serial port output ### ERROR ### Please RESET the board ###, And then it goes into an endless loop