34 */ 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;