U-Boot中global_data数据结构

在start_armboot()函数中，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。分别定义在./include/asm-arm/global_data.h和./include/asm-arm/u-boot.h

1、gd_t: global data数据结构定义，位于文件include/asm-arm/global_data.h。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，指定占用寄存器R8。

/*
*The following data structure is placed in some memory wich is
*available very early after boot (like DPRAM on MPC8xx/MPC82xx, or
*some locked parts of the data cache) to allow for a minimum set of
*global variables during system initialization (until we have set
*up the memory controller so that we can use RAM).
*
* Keep it*SMALL* and remember to set CFG_GBL_DATA_SIZE > sizeof(gd_t)
*CFG_GBL_DATA_SIZE在config文件中定义，start.S中会根据这个值分配栈空间给global_data
*/

ypedef struct global_data {
bd_t *bd;                                //struct board_info指针，保存板子信息
unsigned long flags;                //指示标志，如设备已经初始化标志等
unsigned long baudrate;          //串口波特率
unsigned long have_console;    //串口初始化标志
unsigned long env_addr;          //Address of Environment struct ，环境参数地址
unsigned long env_valid;          //环境参数CRC检验有效标志
unsigned long fb_base;            //frame buffer的基址
#ifdefCONFIG_VFD
unsigned char vfd_type;            /*display type */
#endif
#if 0
unsigned long cpu_clk;            /* CPU clock in Hz! */
unsignedlong bus_clk;
unsigned long ram_size;            /*RAM size */
unsigned long reset_status;      /*reset status register at boot */
#endif
void **jt;                                    /*jump table */
} gd_t;

位于下图所示CFG_GBL_DATA_SIZE位置,即全局配置数据区

/*
*Global Data Flags
*/

#defineGD_FLG_RELOC0x00001      /*Code was relocated to RAM */
#define GD_FLG_DEVINIT 0x00002    /*Devices have been initialized */
#define GD_FLG_SILENT0x00004      /*Silent mode */
#define GD_FLG_POSTFAIL 0x00008  /*Critical POST test failed */

#define GD_FLG_POSTSTOP 0x00010  /*POST seqeunce aborted */

#define GD_FLG_LOGINIT 0x00020    /*Log Buffer has been initialized */

#defineGD_FLG_DISABLE_CONSOLE 0x00040 /*Disable console (in & out) */
#defineDECLARE_GLOBAL_DATA_PTR register volatile gd_t *gd asm ("r8")