Exynos4412 Uboot 移植（六）—— 相关知识补充

Uboot版本：u-boot-2013.01

一、gd结构体的定义与使用

gd_t 和 bd_t 是u-boot中两个重要的数据结构，在初始化操作很多都要靠这两个数据结构来保存或传递。

gd_t 定义在/u-boot-2013.01/arch/arm/include/asm/global_data.h

bd_t 定义在 ./include/asm-arm/u-boot.h

1、gd_t : global data数据结构定义

位于文件/u-boot-2013.01/arch/arm/include/asm/global_data.h 中。其成员主要是一些全局的系统初始化参数。

当使用gd_t 时需用宏定义进行声明DECLARE_GLOBAL_DATA_PTR

从这个宏的定义可以看出，gd是一个保存在ARM的r8寄存器中的gd_t结构体的指针。指定占用寄存器R8。

typedef	struct	global_data {
	bd_t		*bd;//struct board_info指针，保存开发板信息
	unsigned long	flags;//指示标志，如设备已经初始化标志等
	unsigned int	baudrate;//串口波特率
	unsigned long	have_console;	//串口初始化标志
#ifdef CONFIG_PRE_CONSOLE_BUFFER
	unsigned long	precon_buf_idx;	/* Pre-Console buffer index */
#endif
	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_FSL_ESDHC
	unsigned long	sdhc_clk;
#endif
#ifdef CONFIG_AT91FAMILY
	/* "static data" needed by at91's clock.c */
	unsigned long	cpu_clk_rate_hz;
	unsigned long	main_clk_rate_hz;
	unsigned long	mck_rate_hz;
	unsigned long	plla_rate_hz;
	unsigned long	pllb_rate_hz;
	unsigned long	at91_pllb_usb_init;
#endif
#ifdef CONFIG_ARM
	/* "static data" needed by most of timer.c on ARM platforms */
	unsigned long	timer_rate_hz;
	unsigned long	tbl;
	unsigned long	tbu;
	unsigned long long	timer_reset_value;
	unsigned long	lastinc;
#endif
#ifdef CONFIG_IXP425
	unsigned long	timestamp;
#endif
	unsigned long	relocaddr;	/* Start address of U-Boot in RAM */
	phys_size_t	ram_size;	/* RAM size */
	unsigned long	mon_len;	/* monitor len */
	unsigned long	irq_sp;		/* irq stack pointer */
	unsigned long	start_addr_sp;	/* start_addr_stackpointer */
	unsigned long	reloc_off;
#if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF))
	unsigned long	tlb_addr;
	unsigned long	tlb_size;
#endif
	const void	*fdt_blob;	/* Our device tree, NULL if none */
	void		**jt;		/* jump table */
	char		env_buf[32];	/* buffer for getenv() before reloc. */
#if defined(CONFIG_POST) || defined(CONFIG_LOGBUFFER)
	unsigned long	post_log_word; /* Record POST activities */
	unsigned long	post_log_res; /* success of POST test */
	unsigned long	post_init_f_time; /* When post_init_f started */
#endif
} gd_t;

2.、bd_t :board info数据结构定义

位于文件u-boot-2013.01/arch/arm/include/asm/u-boot.h。保存板子参数。

typedef struct bd_info {
	unsigned int	bi_baudrate;	/* 串口波特率 */
    ulong	        bi_arch_number;	/* 开发板机器ID */
    ulong	        bi_boot_params;	/* 启动参数 */
	unsigned long	bi_arm_freq; /* arm frequency */
	unsigned long	bi_dsp_freq; /* dsp core frequency */
	unsigned long	bi_ddr_freq; /* ddr frequency */
    struct				/* RAM configuration */
    {
	ulong start;
	ulong size;
    }			bi_dram[CONFIG_NR_DRAM_BANKS];
} bd_t;