《uboot源码解析(二)启动第二阶段分析》

1.start_armboot分析

根据上一文章得知，在uboot第一阶段最后会调用start_armboot。接下来就继续分析一下start_armboot这个函数（~/lib_arm/board.c）

void start_armboot (void)
{
    init_fnc_t **init_fnc_ptr;
    char *s;
#ifndef CFG_NO_FLASH
    ulong size;
#endif
#if defined(CONFIG_VFD) || defined(CONFIG_LCD)
    unsigned long addr;
#endif

    /* Pointer is writable since we allocated a register for it */
　　//给gt_t这个结构体分配内存，gd是一个在uboot中非常重要的参数，后面会经常看到
    gd = (gd_t*)(_armboot_start - CFG_MALLOC_LEN - sizeof(gd_t));
    /* compiler optimization barrier needed for GCC >= 3.4 */
    __asm__ __volatile__("": : :"memory");

    memset ((void*)gd, 0, sizeof (gd_t));
    gd->bd = (bd_t*)((char*)gd - sizeof(bd_t));
    memset (gd->bd, 0, sizeof (bd_t));

    monitor_flash_len = _bss_start - _armboot_start;
　　//进行一系列初始化，包括cpu初始化，单板初始化等
    for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
        if ((*init_fnc_ptr)() != 0) {
            hang ();
        }
    }

#ifndef CFG_NO_FLASH
    /* configure available FLASH banks */
　　//初始化nor flash（虽然NOR FLASH和NAND FLASH都是flash，但是一般说的flash就是NOR FLASH，NAND就是NAND FLASH）
    size = flash_init ();
    display_flash_config (size);
#endif /* CFG_NO_FLASH */

#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 */
    addr = (_bss_end + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1);
    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 */
　　//内存初始化，之后再uboot上也可以进行malloc和free
    mem_malloc_init (_armboot_start - CFG_MALLOC_LEN);

#if (CONFIG_COMMANDS & CFG_CMD_NAND)
    puts ("NAND:  ");
　　//NAND Flash初始化
    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;
        char tmp[64];

        i = getenv_r ("ethaddr", tmp, sizeof (tmp));
        s = (i > 0) ? tmp : NULL;

        for (reg = 0; reg < 6; ++reg) {
            gd->bd->bi_enetaddr[reg] = s ? simple_strtoul (s, &e, 16) : 0;
            if (s)
                s = (*e) ? e + 1 : e;
        }

#ifdef CONFIG_HAS_ETH1
        i = getenv_r ("eth1addr", tmp, sizeof (tmp));
        s = (i > 0) ? tmp : NULL;

        for (reg = 0; reg < 6; ++reg) {
            gd->bd->bi_enet1addr[reg] = s ? simple_strtoul (s, &e, 16) : 0;
            if (s)
                s = (*e) ? e + 1 : e;
        }
#endif
    }

    devices_init ();    /* get the devices list going. */

#ifdef CONFIG_CMC_PU2
    load_sernum_ethaddr ();
#endif /* CONFIG_CMC_PU2 */

    jumptable_init ();

    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);
    }
#if (CONFIG_COMMANDS & CFG_CMD_NET)
    if ((s = getenv ("bootfile")) != NULL) {
        copy_filename (BootFile, s, sizeof (BootFile));
    }
#endif    /* CFG_CMD_NET */

#ifdef BOARD_LATE_INIT
    board_late_init ();
#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 (;;) {
　　　　//进入main循环
        main_loop ();
    }

    /* NOTREACHED - no way out of command loop except booting */
}

所以start_armboot主要是在c坏境中对一些硬件设备进行一系列的初始化，然后跳转才main中。

 

main_loop

void main_loop (void)
{
#ifndef CFG_HUSH_PARSER
    static char lastcommand[CFG_CBSIZE] = { 0, };
    int len;
    int rc = 1;
    int flag;
#endif

#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)
    char *s;
    int bootdelay;
#endif
#ifdef CONFIG_PREBOOT
    char *p;
#endif
#ifdef CONFIG_BOOTCOUNT_LIMIT
    unsigned long bootcount = 0;
    unsigned long bootlimit = 0;
    char *bcs;
    char bcs_set[16];
#endif /* CONFIG_BOOTCOUNT_LIMIT */

#if defined(CONFIG_VFD) && defined(VFD_TEST_LOGO)
    ulong bmp = 0;        /* default bitmap */
    extern int trab_vfd (ulong bitmap);

#ifdef CONFIG_MODEM_SUPPORT
    if (do_mdm_init)
        bmp = 1;    /* alternate bitmap */
#endif
    trab_vfd (bmp);
#endif    /* CONFIG_VFD && VFD_TEST_LOGO */

#ifdef CONFIG_BOOTCOUNT_LIMIT
    bootcount = bootcount_load();
    bootcount++;
    bootcount_store (bootcount);
    sprintf (bcs_set, "%lu", bootcount);
    setenv ("bootcount", bcs_set);
    bcs = getenv ("bootlimit");
    bootlimit = bcs ? simple_strtoul (bcs, NULL, 10) : 0;
#endif /* CONFIG_BOOTCOUNT_LIMIT */

#ifdef CONFIG_MODEM_SUPPORT
    debug ("DEBUG: main_loop:   do_mdm_init=%d\n", do_mdm_init);
    if (do_mdm_init) {
        char *str = strdup(getenv("mdm_cmd"));
        setenv ("preboot", str);  /* set or delete definition */
        if (str != NULL)
            free (str);
        mdm_init(); /* wait for modem connection */
    }
#endif  /* CONFIG_MODEM_SUPPORT */

#ifdef CONFIG_VERSION_VARIABLE
    {
        extern char version_string[];

        setenv ("ver", version_string);  /* set version variable */
    }
#endif /* CONFIG_VERSION_VARIABLE */

#ifdef CFG_HUSH_PARSER
    u_boot_hush_start ();
#endif

#ifdef CONFIG_AUTO_COMPLETE
    install_auto_complete();
#endif

#ifdef CONFIG_PREBOOT
    if ((p = getenv ("preboot")) != NULL) {
# ifdef CONFIG_AUTOBOOT_KEYED
        int prev = disable_ctrlc(1);    /* disable Control C checking */
# endif

# ifndef CFG_HUSH_PARSER
        run_command (p, 0);
# else
        parse_string_outer(p, FLAG_PARSE_SEMICOLON |
                    FLAG_EXIT_FROM_LOOP);
# endif

# ifdef CONFIG_AUTOBOOT_KEYED
        disable_ctrlc(prev);    /* restore Control C checking */
# endif
    }
#endif /* CONFIG_PREBOOT */

#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)
    s = getenv ("bootdelay");
    bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;

    debug ("### main_loop entered: bootdelay=%d\n\n", bootdelay);

# ifdef CONFIG_BOOT_RETRY_TIME
    init_cmd_timeout ();
# endif    /* CONFIG_BOOT_RETRY_TIME */

#ifdef CONFIG_BOOTCOUNT_LIMIT
　　//倒计时，如果是规定时间按下空格，就进入命令行模式
    if (bootlimit && (bootcount > bootlimit)) {
        printf ("Warning: Bootlimit (%u) exceeded. Using altbootcmd.\n",
                (unsigned)bootlimit);
        s = getenv ("altbootcmd");
    }
    else
#endif /* CONFIG_BOOTCOUNT_LIMIT */
        s = getenv ("bootcmd");

    debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");

    if (bootdelay >= 0 && s && !abortboot (bootdelay)) {
# ifdef CONFIG_AUTOBOOT_KEYED
        int prev = disable_ctrlc(1);    /* disable Control C checking */
# endif

# ifndef CFG_HUSH_PARSER
        run_command (s, 0);
# else
        parse_string_outer(s, FLAG_PARSE_SEMICOLON |
                    FLAG_EXIT_FROM_LOOP);
# endif

# ifdef CONFIG_AUTOBOOT_KEYED
        disable_ctrlc(prev);    /* restore Control C checking */
# endif
    }

# ifdef CONFIG_MENUKEY
    if (menukey == CONFIG_MENUKEY) {
        s = getenv("menucmd");
        if (s) {
# ifndef CFG_HUSH_PARSER
        run_command (s, 0);
# else
        parse_string_outer(s, FLAG_PARSE_SEMICOLON |
                    FLAG_EXIT_FROM_LOOP);
# endif
        }
    }
#endif /* CONFIG_MENUKEY */
#endif    /* CONFIG_BOOTDELAY */

#ifdef CONFIG_AMIGAONEG3SE
    {
        extern void video_banner(void);
        video_banner();
    }
#endif

    /*
     * Main Loop for Monitor Command Processing
     */
#ifdef CFG_HUSH_PARSER
    parse_file_outer();
    /* This point is never reached */
    for (;;);
#else
    for (;;) {
#ifdef CONFIG_BOOT_RETRY_TIME
        if (rc >= 0) {
            /* Saw enough of a valid command to
             * restart the timeout.
             */
            reset_cmd_timeout();
        }
#endif
　　　　　//获取命令，就是平常在命令行界面输入命令，会从这边读取进来
        len = readline (CFG_PROMPT);

        flag = 0;    /* assume no special flags for now */
        if (len > 0)
            strcpy (lastcommand, console_buffer);
        else if (len == 0)
            flag |= CMD_FLAG_REPEAT;
#ifdef CONFIG_BOOT_RETRY_TIME
        else if (len == -2) {
            /* -2 means timed out, retry autoboot
             */
            puts ("\nTimed out waiting for command\n");
# ifdef CONFIG_RESET_TO_RETRY
            /* Reinit board to run initialization code again */
            do_reset (NULL, 0, 0, NULL);
# else
            return;        /* retry autoboot */
# endif
        }
#endif

        if (len == -1)
            puts ("<INTERRUPT>\n");
        else
　　　　　　　//解析命令，然后运行
            rc = run_command (lastcommand, flag);

        if (rc <= 0) {
            /* invalid command or not repeatable, forget it */
            lastcommand[0] = 0;
        }
    }
#endif /*CFG_HUSH_PARSER*/
}

main_loop函数主要是对各种环境变量进行获取以及解析，然后做出相对应的动作。