U-Boot源代码阅读笔记（三）—— 对board.c的分析

wxmtwfx

以arm为例，文件位于lib_arm/board.c，主要分析start_armboot等相关函数
global data数据结构定义，位于文件 include/asm-arm/global_data.h
#ifndef    __ASM_GBL_DATA_H#define __ASM_GBL_DATA_H/* * 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，参见对start.S的分析stack_setup部分 */typedef    struct    global_data {    bd_t        *bd;    /* board info, 参见 include/asm-arm/u-boot.h */    unsigned long    flags;    unsigned long    baudrate;    unsigned long    have_console;    /* serial_init() was called */    unsigned long    reloc_off;    /* Relocation Offset */    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_VFD    unsigned char    vfd_type;    /* display type */#endif    unsigned long    cpu_clk;    /* CPU clock in Hz!        */    unsigned long    bus_clk;    unsigned long    ram_size;    /* RAM size */    unsigned long    reset_status;    /* reset status register at boot */    void        **jt;        /* jump table */} gd_t;/* * Global Data Flags */#define    GD_FLG_RELOC    0x00001        /* Code was relocated to RAM        */#define    GD_FLG_DEVINIT    0x00002        /* Devices have been initialized    */#define    GD_FLG_SILENT    0x00004        /* Silent mode                */#define DECLARE_GLOBAL_DATA_PTR     register volatile gd_t *gd asm ("r8")    /* 定义gd为gd_t类型指针,存储在寄存器r8中 *//* register:表示变量对于执行速度非常重要，因此应该放在机器的寄存器中（寄存器独立于内存，通常在处理器芯片上） *//* volatile:用于指定变量的值可以由外部过程异步修改，例如中断例程 */#endif /* __ASM_GBL_DATA_H */
board info数据结构定义，位于文件 include/asm-arm/u-boot.h
#ifndef _U_BOOT_H_#define _U_BOOT_H_    1typedef struct bd_info {    int            bi_baudrate;    /* serial console baudrate */    unsigned long    bi_ip_addr;    /* IP Address */    unsigned char    bi_enetaddr[6]; /* Ethernet adress */    struct environment_s           *bi_env;    /* environment struct */    ulong            bi_arch_number;    /* unique id for this board */    ulong            bi_boot_params;    /* where this board expects params */    struct                /* RAM configuration */    {    ulong start;    ulong size;    } bi_dram[CONFIG_NR_DRAM_BANKS];    /* 每个DRAM bank的起始地址和大小，CONFIG_NR_DRAM_BANKS 定义DRAM的bank数 */} bd_t;#define bi_env_data bi_env->data#define bi_env_crc  bi_env->crc#endif    /* _U_BOOT_H_ */
init sequence
/* * All attempts to come up with a "common" initialization sequence * that works for all boards and architectures failed: some of the * requirements are just _too_ different. To get rid of the resulting * mess of board dependent #ifdef'ed code we now make the whole * initialization sequence configurable to the user. * * The requirements for any new initalization function is simple: it * receives a pointer to the "global data" structure as it's only * argument, and returns an integer return code, where 0 means * "continue" and != 0 means "fatal error, hang the system". */typedef int (init_fnc_t) (void);init_fnc_t *init_sequence[] = {    cpu_init,        /* basic cpu dependent setup */    init_baudrate,        /* initialze baudrate settings */    serial_init,        /* serial communications setup */    board_init,        /* basic board dependent setup */    interrupt_init,        /* set up exceptions */    env_init,        /* initialize environment */    console_init_f,        /* stage 1 init of console */    display_banner,        /* say that we are here */    dram_init,        /* configure available RAM banks */    display_dram_config,#if defined(CONFIG_VCMA9) || defined (CONFIG_CMC_PU2)    checkboard,#endif    NULL,};
start_armboot
void start_armboot (void){    DECLARE_GLOBAL_DATA_PTR;    /* 声明全局数据指针 */    ulong size;    init_fnc_t **init_fnc_ptr;    /* init sequence */    char *s;#if defined(CONFIG_VFD) || defined(CONFIG_LCD)    unsigned long addr;#endif    /* Pointer is writable since we allocated a register for it */ —— gd为gd_t类型指针,存储在寄存器r8中     gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));    /*  global data地址，栈空间分配参见start.S stack_setup部分 */    /* compiler optimization barrier needed for GCC >= 3.4 */    __asm__ __volatile__("": : :"memory");[color="#000000"]    /* [color="#000000"]内联汇编语句__asm__("":::"memory")向GCC声明，在此内联汇编语句出现的位置内存内容可能改变[color="#000000"]了[color="#000000"]，    所以[color="#000000"]GCC在编译的时候，会将此因素考虑进去，而[color="#000000"]不会对代码进行优化及重新排序等操作,这样GCC会老老实实的生成汇编代码 [color="#000000"]*/    memset ((void*)gd, 0, sizeof (gd_t));    gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));    /* board info 地址*/    memset (gd->bd, 0, sizeof (bd_t));    monitor_flash_len = _bss_start - _armboot_start;    /* .text段和.data段的总长 */    for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {    /* 按照initialization sequence进行初始化 */        if ((*init_fnc_ptr)() != 0) {    /* where 0 means "continue" and != 0 means "fatal error, hang the system". */            hang ();        }    }    puts("Init flash...\n");    /* configure available FLASH banks */    size = flash_init ();    /* init nor flash */    display_flash_config (size);#ifdef CONFIG_VFD#    ifndef PAGE_SIZE#      define PAGE_SIZE 4096#    endif    /*     * reserve memory for VFD display (always full pages)     */    /* bss_end is defined in the board-specific linker script， defined in start.S */     addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);    /* round up to nearest full page */    size = vfd_setmem (addr);    gd->fb_base = addr;#endif /* CONFIG_VFD */#ifdef CONFIG_LCD#    ifndef PAGE_SIZE#      define PAGE_SIZE 4096#    endif    /*     * reserve memory for LCD display (always full pages)     */    /* bss_end is defined in the board-specific linker script */    addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);    size = lcd_setmem (addr);    gd->fb_base = addr;#endif /* CONFIG_LCD */    /* armboot_start is defined in the board-specific linker script */    mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);#if (CONFIG_COMMANDS & CFG_CMD_NAND)    puts ("NAND:");    nand_init();        /* go init the NAND */#endif#ifdef CONFIG_HAS_DATAFLASH    AT91F_DataflashInit();    dataflash_print_info();#endif    /* initialize environment */    env_relocate ();#ifdef CONFIG_VFD    /* must do this after the framebuffer is allocated */    drv_vfd_init();#endif /* CONFIG_VFD */    /* IP Address */    gd->bd->bi_ip_addr = getenv_IPaddr ("ipaddr");    /* MAC Address */    {        int i;        ulong reg;        char *s, *e;        uchar tmp[64];        i = getenv_r ("ethaddr", tmp, sizeof (tmp));        s = (i > 0) ? tmp : NULL;        for (reg = 0; reg             gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) : 0;            if (s)                s = (*e) ? e + 1 : e;        }    }    devices_init ();    /* get the devices list going. */#ifdef CONFIG_CMC_PU2    load_sernum_ethaddr ();#endif /* CONFIG_CMC_PU2 */    jumptable_init ();    /* init jump table */    console_init_r ();    /* fully init console as a device */#if defined(CONFIG_MISC_INIT_R)    /* miscellaneous platform dependent initialisations */    misc_init_r ();#endif    /* enable exceptions */    enable_interrupts ();    /* Perform network card initialisation if necessary */#ifdef CONFIG_DRIVER_CS8900    cs8900_get_enetaddr (gd->bd->bi_enetaddr);#endif#if defined(CONFIG_DRIVER_SMC91111) || defined (CONFIG_DRIVER_LAN91C96)    if (getenv ("ethaddr")) {        smc_set_mac_addr(gd->bd->bi_enetaddr);    }#endif /* CONFIG_DRIVER_SMC91111 || CONFIG_DRIVER_LAN91C96 */    /* Initialize from environment */    if ((s = getenv ("loadaddr")) != NULL) {        load_addr = simple_strtoul (s, NULL, 16);    /* load address */    }#if (CONFIG_COMMANDS & CFG_CMD_NET)    if ((s = getenv ("bootfile")) != NULL) {        copy_filename (BootFile, s, sizeof (BootFile));    /* net boot file */    }#endif    /* CFG_CMD_NET */#ifdef BOARD_LATE_INIT    board_late_init ();    /* init your board */#endif#if (CONFIG_COMMANDS & CFG_CMD_NET)#if defined(CONFIG_NET_MULTI)    puts ("Net:   ");#endif    eth_initialize(gd->bd);#endif    /* main_loop() can return to retry autoboot, if so just run it again. */    for (;;) {        main_loop ();    }    /* NOTREACHED - no way out of command loop except booting */}
               
               
               

本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u2/72751/showart_1095304.html