bd_t和gd_t是u-boot中兩個(gè)重要的數(shù)據(jù)結(jié)構(gòu)，初始化操作中很多全局變量都要靠這兩個(gè)數(shù)據(jù)結(jié)構(gòu)來保存或傳遞。

分別定義在include/asm-arm/u-boot.h和include/asm-arm/global_data.h中。

一、bd_t?

（1）board info數(shù)據(jù)結(jié)構(gòu)定義，主要是用來保存板子參數(shù)。

（2）結(jié)構(gòu)體定義

typedef struct bd_info {int bi_baudrate; /* serial console baudrate */unsigned long bi_ip_addr; /* IP Address *//*開發(fā)板ID，該變量標(biāo)識(shí)每一種開發(fā)板相關(guān)的ID，該值將傳遞給內(nèi)核；如果這個(gè)參數(shù)與內(nèi)核配置的不相同，那么內(nèi)核啟動(dòng)解壓縮完成后將出現(xiàn)“Error : a”錯(cuò)誤；開發(fā)板ID可以在內(nèi)核arch / arm / tools / mach - types中查看 */ulong bi_arch_number; /* unique id for this board*/ulong bi_boot_params; /* where this board expects params u-boot傳遞給內(nèi)核的參數(shù)的保存地址*/struct /* RAM configuration 內(nèi)存的起始地址及大小 */{ulong start;ulong size;} bi_dram[CONFIG_NR_DRAM_BANKS];} bd_t;
二、gd_t?

（1）global data數(shù)據(jù)結(jié)構(gòu)定義，其成員主要是一些全局的系統(tǒng)初始化參數(shù)。當(dāng)使用gd_t時(shí)需用宏定義進(jìn)行聲明：DECLARE_GLOBAL_DATA_PTR，指定占用寄存器R8。

（2）結(jié)構(gòu)體定義

typedef struct global_data {bd_t *bd; //與板子相關(guān)的結(jié)構(gòu)，同上unsigned long flags; //指示標(biāo)志，如設(shè)備已經(jīng)初始化標(biāo)志等unsigned long baudrate; //串口波特率unsigned long have_console; /* serial_init() was called */ //串口初始化標(biāo)志#ifdef CONFIG_PRE_CONSOLE_BUFFER //宏未定義unsigned long precon_buf_idx; /* Pre-Console buffer index */#endifunsigned long env_addr; /* Address of Environment struct */ //環(huán)境變量參數(shù)地址unsigned long env_valid; /* Checksum of Environment valid? */ //檢驗(yàn)環(huán)境變量參數(shù)是否有效unsigned long fb_base; /* base address of frame buffer */ // frame buffer基址#ifdef CONFIG_FSL_ESDHC //宏未在板子相關(guān)頭文件中定義unsigned long sdhc_clk;#endif#ifdef CONFIG_AT91FAMILY //宏未在板子相關(guān)頭文件中定義/* "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 //宏未定義/* "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 //宏未在板子相關(guān)頭文件中定義unsigned long timestamp;#endifunsigned long relocaddr; /* Start address of U-Boot in RAM */ //u-boot自搬移至內(nèi)存后的起始地址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)) //宏未定義unsigned long tlb_addr;#endifconst 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) //宏未定義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;

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