uboot全局数据gd_t、bd_t和device_t

gd_t定义在include/asm-arm/global_data.h

33 /* Keep it *SMALL* and remember to set CFG_GBL_DATA_SIZE > sizeof(gd_t)
34 */

36 typedef struct global_data {
37 bd_t *bd;
38 unsigned long flags;
39 unsigned long baudrate;
40 unsigned long have_console; /* serial_init() was called */
41 unsigned long reloc_off; /* Relocation Offset */
42 unsigned long env_addr; /* Address of Environment struct */
43 unsigned long env_valid; /* Checksum of Environment valid? */
44 unsigned long fb_base; /* base address of frame buffer */
45 #ifdef CONFIG_VFD
46 unsigned char vfd_type; /* display type */
47 #endif
48 #if 0
49 unsigned long cpu_clk; /* CPU clock in Hz! */
50 unsigned long bus_clk;
51 phys_size_t ram_size; /* RAM size */
52 unsigned long reset_status; /* reset status register at boot */
53 #endif
54 void **jt; /* jump table */
55 } gd_t;

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

这个声明告诉编译器使用寄存器r8来存储gd_t类型的指针gd，即这个定义声明了一个指针，并且指明了它的存储位置。

register表示变量放在机器的寄存器

volatile用于指定变量的值可以由外部过程异步修改。

并且这个指针在start_armboot()（board.c)中被初始化：

/* Pointer is writable since we allocated a register for it */

gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));

这样，gd就指向的一个可用的内存地址了。

-------------------------------------------------------------------------------------------------------------

bd_t定义于include/asm-arm/u-boot.h

39 typedef struct bd_info {
40 int bi_baudrate; /* serial console baudrate */
41 unsigned long bi_ip_addr; /* IP Address */
42 unsigned char bi_enetaddr[6]; /* Ethernet adress */
43 struct environment_s *bi_env;
44 ulong bi_arch_number; /* unique id for this board */
45 ulong bi_boot_params; /* where this board expects params */
46 struct /* RAM configuration */
47 {
48 ulong start;
49 ulong size;
50 } bi_dram[CONFIG_NR_DRAM_BANKS];
51 #ifdef CONFIG_HAS_ETH1
52 /* second onboard ethernet port */
53 unsigned char bi_enet1addr[6];
54 #endif
55 } bd_t;
56
57 #define bi_env_data bi_env->data
58 #define bi_env_crc bi_env->crc

------------------------------------------------------------------------------------------------

device_t定义于include/devices.h，是对串口设备文件的描述。

29 /*
30 * CONSOLE DEVICES
31 */
32
33 #define DEV_FLAGS_INPUT 0x00000001 /* Device can be used as input console */
34 #define DEV_FLAGS_OUTPUT 0x00000002 /* Device can be used as output console */
35 #define DEV_FLAGS_SYSTEM 0x80000000 /* Device is a system device */
36 #define DEV_EXT_VIDEO 0x00000001 /* Video extensions supported */
37
38 /* Device information */
39 typedef struct {
40 int flags; /* Device flags: input/output/system */
41 int ext; /* Supported extensions */
42 char name[16]; /* Device name */
43
44 /* GENERAL functions */
45
46 int (*start) (void); /* To start the device */
47 int (*stop) (void); /* To stop the device */
48
49 /* OUTPUT functions */
50
51 void (*putc) (const char c); /* To put a char */
52 void (*puts) (const char *s); /* To put a string (accelerator) */
53
54 /* INPUT functions */
55
56 int (*tstc) (void); /* To test if a char is ready... */
57 int (*getc) (void); /* To get that char */
58
59 /* Other functions */
60
61 void *priv; /* Private extensions */
62 } device_t;