uboot学习之BL3的流程

BL2的最后通过汇编调用了board_init_r函数，此时进入BL3的阶段，此时的主要工作：

这一阶段涉及的文件及任务如下

arch/arm/lib/board.c
           1. board_init_r()是进入定制板目录的入口
common/main.c
           2. main_loop()中关闭中断，执行命令以及加载引导内核

下面分析一下board_init_r函数：

/*
 ************************************************************************
 *
 * This is the next part if the initialization sequence: we are now
 * running from RAM and have a "normal" C environment, i. e. global
 * data can be written, BSS has been cleared, the stack size in not
 * that critical any more, etc.
 *
 ************************************************************************
 */
void board_init_r(gd_t *id, ulong dest_addr)
{
    ...
    bd_t *bd;
    ...
    gd = id;
    bd = gd->bd;
 
    gd->flags |= GD_FLG_RELOC;    /* tell others: relocation done */
 
    monitor_flash_len = _end_ofs;
 
    ...
    debug("monitor flash len: %08lX\n", monitor_flash_len);
    board_init();    /* Setup chipselects */    

上述代码的作用是对gd和bd进行赋值，其中monitor_flash_len为整个U-Boot的长度。

 malloc_start = dest_addr - TOTAL_MALLOC_LEN - sizeof(struct spare_boot_head_t);
...
/* The Malloc area is immediately below the monitor copy in DRAM */
    mem_malloc_init (malloc_start, TOTAL_MALLOC_LEN);

对SDRAM中的malloc空间进行清零初始化。

#if !defined(CONFIG_SYS_NO_FLASH)
    puts("Flash: ");
 
    flash_size = flash_init();
    if (flash_size > ) {
# ifdef CONFIG_SYS_FLASH_CHECKSUM
        print_size(flash_size, "");
        /*
         * Compute and print flash CRC if flashchecksum is set to 'y'
         *
         * NOTE: Maybe we should add some WATCHDOG_RESET()? XXX
         */
        s = getenv("flashchecksum");
        if (s && (*s == 'y')) {
            printf("  CRC: %08X", crc32(,
                (const unsigned char *) CONFIG_SYS_FLASH_BASE,
                flash_size));
        }
        putc('\n');
# else    /* !CONFIG_SYS_FLASH_CHECKSUM */
        print_size(flash_size, "\n");
# endif /* CONFIG_SYS_FLASH_CHECKSUM */
    } else {
        puts(failed);
        hang();
    }
#endif

上述代码的作用是计算FLASH的大小，并把它通过串口显示在控制台上。由于没有定义CONFIG_SYS_FLASH_CHECKSUM，所以没有执行CRC的校验和。其中flash_init函数是在drivers/mtd目录下的cfi_flash.c文件内（因为include/configs/smdk2410.h中定义了CONFIG_FLASH_CFI_DRIVER）。

    /* set up exceptions */
    interrupt_init();
    /* enable exceptions */
    enable_interrupts();

interrupt_init函数是建立IRQ中断堆栈，enable_interrupts函数是使能IRQ中断，它们都是在arch/arm/lib目录下的interrupts.c文件中定义的。

...
/* initialize environment */
    env_relocate();

初始化环境变量，由于gd->env_valid等于0，所以在这里设置的是缺省环境变量。env_relocate函数是在common目录下的env_common.c文件中定义的。

#if defined(CONFIG_CMD_PCI) || defined(CONFIG_PCI)
    arm_pci_init();
#endif

初始化PCI。

    /* IP Address */
    gd->bd->bi_ip_addr = getenv_IPaddr("ipaddr");
    stdio_init();    /* get the devices list going. */
    jumptable_init();
#if defined(CONFIG_API)
    /* Initialize API */
    api_init();
#endif
 
    console_init_r();    /* fully init console as a device */

上面代码的作用分别对应：

设置IP地址。

初始化各类外设，如IIC、LCD、键盘、USB等，当然只有在定义了这些外设的前提下，才对这些外设进行初始化。该函数是在common目录下的stdio.c文件中定义的。

初始化跳转表gd->jt，该跳转表是一个函数指针数组，它定义了U-Boot中基本的常用函数库。该函数是在common目录下的exports.c文件中定义的。

初始化API。

初始化控制台，即标准输入、标准输出和标准错误，在这里都是串口。该函数是在common目录下的console.c文件中定义的。

    /* Initialize from environment */
    s = getenv("loadaddr");
    if (s != NULL)
        load_addr = simple_strtoul(s, NULL, );

从环境变量中获取loadaddr参数，得到需要加载的地址。

#if defined(CONFIG_CMD_NET)
    s = getenv("bootfile");
    if (s != NULL)
        copy_filename(BootFile, s, sizeof(BootFile));
#endif

从环境变量中获取bootfile参数，得到通过TFTP加载的镜像文件名。

#if defined(CONFIG_CMD_NET)
#if defined(CONFIG_NET_MULTI)
    puts("Net:   ");
#endif
    eth_initialize(gd->bd);
#if defined(CONFIG_RESET_PHY_R)
    debug("Reset Ethernet PHY\n");
    reset_phy();
#endif
#endif

初始化以太网，其中eth_initialize函数是在net目录下的eth.c文件中定义的。

    ...
　　 /* main_loop() can return to retry autoboot, if so just run it again. */
    for (;;)
    {
        main_loop();
    }
    hang();
    /* NOTREACHED - no way out of command loop except booting */
}

board_init_r函数的最后就是执行一个死循环，调用main_loop函数。该函数是在common目录下的main.c文件内定义的。

总结：

3.接下来分析main_loop函数：

void main_loop (void)
{
#ifndef CONFIG_SYS_HUSH_PARSER
    static char lastcommand[CONFIG_SYS_CBSIZE] = { , };
    int len;
    int rc = ;
    int flag;
#endif

声明一些hush参数。关于hush后面会讲到。

#if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)
    char *s;
    int bootdelay;
#endif

声明启动延时需要的参数。

#ifdef CONFIG_SYS_HUSH_PARSER
    u_boot_hush_start ();
#endif

初始化hush功能。稍后再说。

  #if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)
      s = getenv ("bootdelay");
      bootdelay = s ? (int)simple_strtol(s, NULL, ) : 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_POST
     if (gd->flags & GD_FLG_POSTFAIL) {
         s = getenv("failbootcmd");
     }
     else
 #endif /* CONFIG_POST */
 #ifdef CONFIG_BOOTCOUNT_LIMIT
     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 >=  && s && !abortboot (bootdelay)) {
 # ifdef CONFIG_AUTOBOOT_KEYED
         int prev = disable_ctrlc();    /* disable Control C checking */
 # endif
 
 # ifndef CONFIG_SYS_HUSH_PARSER
         run_command (s, );
 # 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 CONFIG_SYS_HUSH_PARSER
             run_command(s, );
 # else
             parse_string_outer(s, FLAG_PARSE_SEMICOLON |
                         FLAG_EXIT_FROM_LOOP);
 # endif
         }
     }
 #endif /* CONFIG_MENUKEY */
 #endif /* CONFIG_BOOTDELAY */

第2行和第3行的含义是从环境变量中获取bootdelay参数，得到自动启动缺省镜像文件的延时（单位是秒）。

其中bootdelay的作用是：uboot正常启动后，会调用main_loop(void)函数，进入main_loop()之后，如果在规定的时间（CONFIG_BOOTDELAY）内，没有检查到任何按键事件的发生，就会去加载OS，并启动系统。

第8行的含义是初始化命令行超时机制。

第25行的含义是从环境变量中获取bootcmd参数，得到在启动延时过程中自动执行的命令。当我们得到了bootcmd参数，bootdelay参数也是大于等于0，并且在启动延时过程中没有按下任意键时，执行第37行的parse_string_outer函数，该函数的作用是解释bootcmd参数

并执行，它是在common目录下的hush.c文件内定义的。

      /*
 2      * Main Loop for Monitor Command Processing
 3      */
  #ifdef CONFIG_SYS_HUSH_PARSER
      parse_file_outer();
      /* This point is never reached */
      for (;;);
  #else
      for (;;) {
 #ifdef CONFIG_BOOT_RETRY_TIME
         if (rc >= ) {
             /* Saw enough of a valid command to
13              * restart the timeout.
14              */
             reset_cmd_timeout();
         }
 #endif
         len = readline (CONFIG_SYS_PROMPT);
 
         flag = ;    /* assume no special flags for now */
         if (len > )
             strcpy (lastcommand, console_buffer);
         else if (len == )
             flag |= CMD_FLAG_REPEAT;
 #ifdef CONFIG_BOOT_RETRY_TIME
         else if (len == -) {
             /* -2 means timed out, retry autoboot
28              */
             puts ("\nTimed out waiting for command\n");
 # ifdef CONFIG_RESET_TO_RETRY
             /* Reinit board to run initialization code again */
             do_reset (NULL, , , NULL);
 # else
             return;        /* retry autoboot */
 # endif
         }
 #endif
 
         if (len == -)
             puts ("<INTERRUPT>\n");
         else
             rc = run_command (lastcommand, flag);
 
         if (rc <= ) {
             /* invalid command or not repeatable, forget it */
             lastcommand[] = ;
         }
     }
 #endif /*CONFIG_SYS_HUSH_PARSER*/
 }

由于在include/configs/smdk2410.h文件中定义了CONFIG_SYS_HUSH_PARSER，所以上面的代码仅仅执行的是第5行至第7行的内容。第5行的parse_file_outer函数是在common目录下的hush.c文件中定义的，它的含义是依次读取命令序列中的命令并执行之，其中在该

函数还调用了parse_stream_outer函数，这个函数体内有一个do-while循环，只有发生语法错误的时候才会跳出该循环，因此一般情况下永远也不会执行上面代码中的第7行内容，而是始终在那个do-while循环体内。

上面说到过如果在CONFIG_BOOTDELAY时间内，用户按下键盘上的任意一个按键，uboot就会进入与用户交互的状态。如果用户在配置文件中定义了CONFIG_SYS_HUSH_PARSER，就会通过parse_file_outer()，去接收并解析用户命令，否则进入一个for（;;）循环，

通过 readline (CONFIG_SYS_PROMPT)接收用户命令，然后调用run_command(cmd,flag)去解析并执行命令。

当在配置文件中定义了CONFIG_SYS_HUSH_PARSER，main_loop会调用parse_file_outer()，进入hush中。其中parse_file_outer()在u-boot\common\hush.c下。

#ifndef __U_BOOT__
static int parse_file_outer(FILE *f)
#else
int parse_file_outer(void)
#endif
{
    int rcode;
    struct in_str input;
#ifndef __U_BOOT__
    setup_file_in_str(&input, f);
#else
    setup_file_in_str(&input);
#endif
    rcode = parse_stream_outer(&input, FLAG_PARSE_SEMICOLON);
    return rcode;
}

/* most recursion does not come through here, the exeception is
 * from builtin_source() */
int parse_stream_outer(struct in_str *inp, int flag)
{
 
    struct p_context ctx;
    o_string temp=NULL_O_STRING;
    int rcode;
#ifdef __U_BOOT__
    int code = ;
#endif
    do {
        ctx.type = flag;
        initialize_context(&ctx);
        update_ifs_map();
        if (!(flag & FLAG_PARSE_SEMICOLON) || (flag & FLAG_REPARSING)) mapset((uchar *)";$&|", );
        inp->promptmode=;
        rcode = parse_stream(&temp, &ctx, inp, '\n');
#ifdef __U_BOOT__
        if (rcode == ) flag_repeat = ;
#endif
        if (rcode !=  && ctx.old_flag != ) {
            syntax();
#ifdef __U_BOOT__
            flag_repeat = ;
#endif
        }
        if (rcode !=  && ctx.old_flag == ) {
            done_word(&temp, &ctx);
            done_pipe(&ctx,PIPE_SEQ);
#ifndef __U_BOOT__
            run_list(ctx.list_head);
#else
            code = run_list(ctx.list_head);
            if (code == -) {    /* exit */
                b_free(&temp);
                code = ;
                /* XXX hackish way to not allow exit from main loop */
                if (inp->peek == file_peek) {
                    printf("exit not allowed from main input shell.\n");
                    continue;
                }
                break;
            }
            if (code == -)
                flag_repeat = ;
#endif
        } else {
            if (ctx.old_flag != ) {
                free(ctx.stack);
                b_reset(&temp);
            }
#ifdef __U_BOOT__
            if (inp->__promptme == ) printf("<INTERRUPT>\n");
            inp->__promptme = ;
#endif
            temp.nonnull = ;
            temp.quote = ;
            inp->p = NULL;
            free_pipe_list(ctx.list_head,);
        }
        b_free(&temp);
    } while (rcode != - && !(flag & FLAG_EXIT_FROM_LOOP));   /* loop on syntax errors, return on EOF */
#ifndef __U_BOOT__
    return ;
#else
    return (code != ) ?  : ;
#endif /* __U_BOOT__ */
}

hush是uboot中命令接收和解析的工具，与uboot原始的命令解析方法相比，该工具更加智能。

这里会在run_list中调用到hush中的run_pipe_real(struct pipe *pi)，在该函数中经过一些列解析，最终会调用到对应的命令执行函数。

/* run_pipe_real() starts all the jobs, but doesn't wait for anything
 * to finish.  See checkjobs().
 *
 * return code is normally -1, when the caller has to wait for children
 * to finish to determine the exit status of the pipe.  If the pipe
 * is a simple builtin command, however, the action is done by the
 * time run_pipe_real returns, and the exit code is provided as the
 * return value.
 *
 * The input of the pipe is always stdin, the output is always
 * stdout.  The outpipe[] mechanism in BusyBox-0.48 lash is bogus,
 * because it tries to avoid running the command substitution in
 * subshell, when that is in fact necessary.  The subshell process
 * now has its stdout directed to the input of the appropriate pipe,
 * so this routine is noticeably simpler.
 */
static int run_pipe_real(struct pipe *pi)
{
    int i;
#ifndef __U_BOOT__
    int nextin, nextout;
    int pipefds[];                /* pipefds[0] is for reading */
    struct child_prog *child;
    struct built_in_command *x;
    char *p;
# if __GNUC__
    /* Avoid longjmp clobbering */
    (void) &i;
    (void) &nextin;
    (void) &nextout;
    (void) &child;
# endif
#else
    int nextin;
    int flag = do_repeat ? CMD_FLAG_REPEAT : ;
    struct child_prog *child;
    cmd_tbl_t *cmdtp;
    char *p;
# if __GNUC__
    /* Avoid longjmp clobbering */
    (void) &i;
    (void) &nextin;
    (void) &child;
# endif
#endif    /* __U_BOOT__ */
 
    nextin = ;
#ifndef __U_BOOT__
    pi->pgrp = -;
#endif
 
    /* Check if this is a simple builtin (not part of a pipe).
     * Builtins within pipes have to fork anyway, and are handled in
     * pseudo_exec.  "echo foo | read bar" doesn't work on bash, either.
     */
    if (pi->num_progs == ) child = & (pi->progs[]);
#ifndef __U_BOOT__
    if (pi->num_progs ==  && child->group && child->subshell == ) {
        int squirrel[] = {-, -, -};
        int rcode;
        debug_printf("non-subshell grouping\n");
        setup_redirects(child, squirrel);
        /* XXX could we merge code with following builtin case,
         * by creating a pseudo builtin that calls run_list_real? */
        rcode = run_list_real(child->group);
        restore_redirects(squirrel);
#else
        if (pi->num_progs ==  && child->group) {
        int rcode;
        debug_printf("non-subshell grouping\n");
        rcode = run_list_real(child->group);
#endif
        return rcode;
    } else if (pi->num_progs ==  && pi->progs[].argv != NULL) {
        for (i=; is_assignment(child->argv[i]); i++) { /* nothing */ }
        if (i!= && child->argv[i]==NULL) {
            /* assignments, but no command: set the local environment */
            for (i=; child->argv[i]!=NULL; i++) {
 
                /* Ok, this case is tricky.  We have to decide if this is a
                 * local variable, or an already exported variable.  If it is
                 * already exported, we have to export the new value.  If it is
                 * not exported, we need only set this as a local variable.
                 * This junk is all to decide whether or not to export this
                 * variable. */
                int export_me=;
                char *name, *value;
                name = xstrdup(child->argv[i]);
                debug_printf("Local environment set: %s\n", name);
                value = strchr(name, '=');
                if (value)
                    *value=;
#ifndef __U_BOOT__
                if ( get_local_var(name)) {
                    export_me=;
                }
#endif
                free(name);
                p = insert_var_value(child->argv[i]);
                set_local_var(p, export_me);
                if (p != child->argv[i]) free(p);
            }
            return EXIT_SUCCESS;   /* don't worry about errors in set_local_var() yet */
        }
        for (i = ; is_assignment(child->argv[i]); i++) {
            p = insert_var_value(child->argv[i]);
#ifndef __U_BOOT__
            putenv(strdup(p));
#else
            set_local_var(p, );
#endif
            if (p != child->argv[i]) {
                child->sp--;
                free(p);
            }
        }
        if (child->sp) {
            char * str = NULL;
 
            str = make_string((child->argv + i));
            parse_string_outer(str, FLAG_EXIT_FROM_LOOP | FLAG_REPARSING);
            free(str);
            return last_return_code;
        }
#ifndef __U_BOOT__
        for (x = bltins; x->cmd; x++) {
            if (strcmp(child->argv[i], x->cmd) ==  ) {
                int squirrel[] = {-, -, -};
                int rcode;
                if (x->function == builtin_exec && child->argv[i+]==NULL) {
                    debug_printf("magic exec\n");
                    setup_redirects(child,NULL);
                    return EXIT_SUCCESS;
                }
                debug_printf("builtin inline %s\n", child->argv[]);
                /* XXX setup_redirects acts on file descriptors, not FILEs.
                 * This is perfect for work that comes after exec().
                 * Is it really safe for inline use?  Experimentally,
                 * things seem to work with glibc. */
                setup_redirects(child, squirrel);
#else
            /* check ";", because ,example , argv consist from
             * "help;flinfo" must not execute
             */
            if (strchr(child->argv[i], ';')) {
                printf ("Unknown command '%s' - try 'help' or use 'run' command\n",
                    child->argv[i]);
                return -;
            }
            /* Look up command in command table */
 
            if ((cmdtp = find_cmd(child->argv[i])) == NULL) {
                printf ("Unknown command '%s' - try 'help'\n", child->argv[i]);
                return -;    /* give up after bad command */
            } else {
                int rcode;
#if defined(CONFIG_CMD_BOOTD)
                /* avoid "bootd" recursion */
                if (cmdtp->cmd == do_bootd) {
                    if (flag & CMD_FLAG_BOOTD) {
                        printf ("'bootd' recursion detected\n");
                        return -;
                    }
                else
                    flag |= CMD_FLAG_BOOTD;
                }
#endif
                /* found - check max args */
                if ((child->argc - i) > cmdtp->maxargs)
                    return cmd_usage(cmdtp);
#endif
                child->argv+=i;  /* XXX horrible hack */
#ifndef __U_BOOT__
                rcode = x->function(child);
#else
                /* OK - call function to do the command */
 
                rcode = (cmdtp->cmd)
(cmdtp, flag,child->argc-i,&child->argv[i]);
                if ( !cmdtp->repeatable )
                    flag_repeat = ;
 
#endif
                child->argv-=i;  /* XXX restore hack so free() can work right */
#ifndef __U_BOOT__
 
                restore_redirects(squirrel);
#endif
 
                return rcode;
            }
        }
#ifndef __U_BOOT__
    }
 
    for (i = ; i < pi->num_progs; i++) {
        child = & (pi->progs[i]);
 
        /* pipes are inserted between pairs of commands */
        if ((i + ) < pi->num_progs) {
            if (pipe(pipefds)<) perror_msg_and_die("pipe");
            nextout = pipefds[];
        } else {
            nextout=;
            pipefds[] = -;
        }
 
        /* XXX test for failed fork()? */
        if (!(child->pid = fork())) {
            /* Set the handling for job control signals back to the default.  */
            signal(SIGINT, SIG_DFL);
            signal(SIGQUIT, SIG_DFL);
            signal(SIGTERM, SIG_DFL);
            signal(SIGTSTP, SIG_DFL);
            signal(SIGTTIN, SIG_DFL);
            signal(SIGTTOU, SIG_DFL);
            signal(SIGCHLD, SIG_DFL);
 
            close_all();
 
            if (nextin != ) {
                dup2(nextin, );
                close(nextin);
            }
            if (nextout != ) {
                dup2(nextout, );
                close(nextout);
            }
            if (pipefds[]!=-) {
                close(pipefds[]);  /* opposite end of our output pipe */
            }
 
            /* Like bash, explicit redirects override pipes,
             * and the pipe fd is available for dup'ing. */
            setup_redirects(child,NULL);
 
            if (interactive && pi->followup!=PIPE_BG) {
                /* If we (the child) win the race, put ourselves in the process
                 * group whose leader is the first process in this pipe. */
                if (pi->pgrp < ) {
                    pi->pgrp = getpid();
                }
                if (setpgid(, pi->pgrp) == ) {
                    tcsetpgrp(, pi->pgrp);
                }
            }
 
            pseudo_exec(child);
        }
 
        /* put our child in the process group whose leader is the
           first process in this pipe */
        if (pi->pgrp < ) {
            pi->pgrp = child->pid;
        }
        /* Don't check for errors.  The child may be dead already,
         * in which case setpgid returns error code EACCES. */
        setpgid(child->pid, pi->pgrp);
 
        if (nextin != )
            close(nextin);
        if (nextout != )
            close(nextout);
 
        /* If there isn't another process, nextin is garbage
           but it doesn't matter */
        nextin = pipefds[];
    }
#endif
    return -;
}

上面关键是这段：

                /* OK - call function to do the command */
 
                rcode = (cmdtp->cmd)
(cmdtp, flag,child->argc-i,&child->argv[i]);
                if ( !cmdtp->repeatable )
                    flag_repeat = ;

通过这段代码调用对应的命令执行函数。cmd_tbl_t的结构如下：

struct cmd_tbl_s {
    char        *name;        /* Command Name            */
    int        maxargs;    /* maximum number of arguments    */
    int        repeatable;    /* autorepeat allowed?        */
                    /* Implementation function    */
    int        (*cmd)(struct cmd_tbl_s *, int, int, char * const []);
    char        *usage;        /* Usage message    (short)    */
#ifdef    CONFIG_SYS_LONGHELP
    char        *help;        /* Help  message    (long)    */
#endif
#ifdef CONFIG_AUTO_COMPLETE
    /* do auto completion on the arguments */
    int        (*complete)(int argc, char * const argv[], char last_char, int maxv, char *cmdv[]);
#endif
};
 
typedef struct cmd_tbl_s    cmd_tbl_t;

对于uboot支持的每一个命令，是通过U_BOOT_CMD宏定义的，他定义了该命令对应的名称name，支持的最大参数rep，重复次数，实现函数cmd，以及输入help命令时，显示的帮助信息usage。

在执行函数cmd中，第一个参数对应该命令结构本身的指针，第二个参数对应flag标记，第三个参数对应参数数目，第四个参数是指针数组，里面存储的是对应参数的指针。