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 > 0) {# ifdef CONFIG_SYS_FLASH_CHECKSUMprint_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(0,(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();#endifconsole_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, 16);

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: ");#endifeth_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_PARSERstatic char lastcommand[CONFIG_SYS_CBSIZE] = { 0, };int len;int rc = 1;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_PARSERu_boot_hush_start ();#endif

初始化hush功能。稍后再说。

1 #if defined(CONFIG_BOOTDELAY) && (CONFIG_BOOTDELAY >= 0)2s = getenv ("bootdelay");3bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;4 5debug ("### main_loop entered: bootdelay=%d\n\n", bootdelay);6 7 # ifdef CONFIG_BOOT_RETRY_TIME8init_cmd_timeout ();9 # endif /* CONFIG_BOOT_RETRY_TIME */10 11 #ifdef CONFIG_POST12if (gd->flags & GD_FLG_POSTFAIL) {13 s = getenv("failbootcmd");14}15else16 #endif /* CONFIG_POST */17 #ifdef CONFIG_BOOTCOUNT_LIMIT18if (bootlimit && (bootcount > bootlimit)) {19 printf ("Warning: Bootlimit (%u) exceeded. Using altbootcmd.\n",20 (unsigned)bootlimit);21 s = getenv ("altbootcmd");22}23else24 #endif /* CONFIG_BOOTCOUNT_LIMIT */25 s = getenv ("bootcmd");26 27debug ("### main_loop: bootcmd=\"%s\"\n", s ? s : "<UNDEFINED>");28 29if (bootdelay >= 0 && s && !abortboot (bootdelay)) {30 # ifdef CONFIG_AUTOBOOT_KEYED31 int prev = disable_ctrlc(1); /* disable Control C checking */32 # endif33 34 # ifndef CONFIG_SYS_HUSH_PARSER35 run_command (s, 0);36 # else37 parse_string_outer(s, FLAG_PARSE_SEMICOLON |38 FLAG_EXIT_FROM_LOOP);39 # endif40 41 # ifdef CONFIG_AUTOBOOT_KEYED42 disable_ctrlc(prev); /* restore Control C checking */43 # endif44}45 46 # ifdef CONFIG_MENUKEY47if (menukey == CONFIG_MENUKEY) {48 s = getenv("menucmd");49 if (s) {50 # ifndef CONFIG_SYS_HUSH_PARSER51 run_command(s, 0);52 # else53 parse_string_outer(s, FLAG_PARSE_SEMICOLON |54FLAG_EXIT_FROM_LOOP);55 # endif56 }57}58 #endif /* CONFIG_MENUKEY */59 #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。

1/*2* Main Loop for Monitor Command Processing3*/4 #ifdef CONFIG_SYS_HUSH_PARSER5parse_file_outer();6/* This point is never reached */7for (;;);8 #else9for (;;) {10 #ifdef CONFIG_BOOT_RETRY_TIME11 if (rc >= 0) {12 /* Saw enough of a valid command to13 * restart the timeout.14 */15 reset_cmd_timeout();16 }17 #endif18 len = readline (CONFIG_SYS_PROMPT);19 20 flag = 0; /* assume no special flags for now */21 if (len > 0)22 strcpy (lastcommand, console_buffer);23 else if (len == 0)24 flag |= CMD_FLAG_REPEAT;25 #ifdef CONFIG_BOOT_RETRY_TIME26 else if (len == -2) {27 /* -2 means timed out, retry autoboot28 */29 puts ("\nTimed out waiting for command\n");30 # ifdef CONFIG_RESET_TO_RETRY31 /* Reinit board to run initialization code again */32 do_reset (NULL, 0, 0, NULL);33 # else34 return; /* retry autoboot */35 # endif36 }37 #endif38 39 if (len == -1)40 puts ("<INTERRUPT>\n");41 else42 rc = run_command (lastcommand, flag);43 44 if (rc <= 0) {45 /* invalid command or not repeatable, forget it */46 lastcommand[0] = 0;47 }48}49 #endif /*CONFIG_SYS_HUSH_PARSER*/50 }

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)#elseint parse_file_outer(void)#endif{int rcode;struct in_str input;#ifndef __U_BOOT__setup_file_in_str(&input, f);#elsesetup_file_in_str(&input);#endifrcode = 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 = 0;#endifdo {ctx.type = flag;initialize_context(&ctx);update_ifs_map();if (!(flag & FLAG_PARSE_SEMICOLON) || (flag & FLAG_REPARSING)) mapset((uchar *)";$&|", 0);inp->promptmode=1;rcode = parse_stream(&temp, &ctx, inp, '\n');#ifdef __U_BOOT__if (rcode == 1) flag_repeat = 0;#endifif (rcode != 1 && ctx.old_flag != 0) {syntax();#ifdef __U_BOOT__flag_repeat = 0;#endif}if (rcode != 1 && ctx.old_flag == 0) {done_word(&temp, &ctx);done_pipe(&ctx,PIPE_SEQ);#ifndef __U_BOOT__run_list(ctx.list_head);#elsecode = run_list(ctx.list_head);if (code == -2) { /* exit */b_free(&temp);code = 0;/* 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 == -1)flag_repeat = 0;#endif} else {if (ctx.old_flag != 0) {free(ctx.stack);b_reset(&temp);}#ifdef __U_BOOT__if (inp->__promptme == 0) printf("<INTERRUPT>\n");inp->__promptme = 1;#endiftemp.nonnull = 0;temp.quote = 0;inp->p = NULL;free_pipe_list(ctx.list_head,0);}b_free(&temp);} while (rcode != -1 && !(flag & FLAG_EXIT_FROM_LOOP)); /* loop on syntax errors, return on EOF */#ifndef __U_BOOT__return 0;#elsereturn (code != 0) ? 1 : 0;#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(structpipe*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[2];/* 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#elseint nextin;int flag = do_repeat ? CMD_FLAG_REPEAT : 0;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 = 0;#ifndef __U_BOOT__pi->pgrp = -1;#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 == 1) child = & (pi->progs[0]);#ifndef __U_BOOT__if (pi->num_progs == 1 && child->group && child->subshell == 0) {int squirrel[] = {-1, -1, -1};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);#elseif (pi->num_progs == 1 && child->group) {int rcode;debug_printf("non-subshell grouping\n");rcode = run_list_real(child->group);#endifreturn rcode;} else if (pi->num_progs == 1 && pi->progs[0].argv != NULL) {for (i=0; is_assignment(child->argv[i]); i++) { /* nothing */ }if (i!=0 && child->argv[i]==NULL) {/* assignments, but no command: set the local environment */for (i=0; 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=0;char *name, *value;name = xstrdup(child->argv[i]);debug_printf("Local environment set: %s\n", name);value = strchr(name, '=');if (value)*value=0;#ifndef __U_BOOT__if ( get_local_var(name)) {export_me=1;}#endiffree(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 = 0; is_assignment(child->argv[i]); i++) {p = insert_var_value(child->argv[i]);#ifndef __U_BOOT__putenv(strdup(p));#elseset_local_var(p, 0);#endifif (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) == 0 ) {int squirrel[] = {-1, -1, -1};int rcode;if (x->function == builtin_exec && child->argv[i+1]==NULL) {debug_printf("magic exec\n");setup_redirects(child,NULL);return EXIT_SUCCESS;}debug_printf("builtin inline %s\n", child->argv[0]);/* 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 -1;}/* 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 -1; /* 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 -1;}elseflag |= CMD_FLAG_BOOTD;}#endif/* found - check max args */if ((child->argc - i) > cmdtp->maxargs)return cmd_usage(cmdtp);#endifchild->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 = 0;#endifchild->argv-=i; /* XXX restore hack so free() can work right */#ifndef __U_BOOT__restore_redirects(squirrel);#endifreturn rcode;}}#ifndef __U_BOOT__}for (i = 0; i < pi->num_progs; i++) {child = & (pi->progs[i]);/* pipes are inserted between pairs of commands */if ((i + 1) < pi->num_progs) {if (pipe(pipefds)<0) perror_msg_and_die("pipe");nextout = pipefds[1];} else {nextout=1;pipefds[0] = -1;}/* 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 != 0) {dup2(nextin, 0);close(nextin);}if (nextout != 1) {dup2(nextout, 1);close(nextout);}if (pipefds[0]!=-1) {close(pipefds[0]); /* 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 < 0) {pi->pgrp = getpid();}if (setpgid(0, pi->pgrp) == 0) {tcsetpgrp(2, pi->pgrp);}}pseudo_exec(child);}/* put our child in the process group whose leader is thefirst process in this pipe */if (pi->pgrp < 0) {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 != 0)close(nextin);if (nextout != 1)close(nextout);/* If there isn't another process, nextin is garbagebut it doesn't matter */nextin = pipefds[0];}#endifreturn -1;}

View Code

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 = 0;

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_LONGHELPchar *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。

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