uboot命令的实现

先分一下，uboot如何解析我们输进去的命令，其中argv[x]就是用来保存每一条指令，uboot支持多条命令一起输入，用分号;隔开

/* Extract arguments */ if ((argc = parse_line (finaltoken, argv)) == 0) {    rc = -1; /* no command at all */ continue; } 

然后是在表中查找是否有输入的命令，后续还要做一些命令合格性的检查

/* Look up command in command table */ if ((cmdtp = find_cmd(argv[0])) == NULL) {    printf ("Unknown command '%s' - try 'help'n", argv[0]);    rc = -1; /* give up after bad command */ continue; } /* found - check max args */ if (argc > cmdtp->maxargs) {    printf ("Usage:n%sn", cmdtp->usage);    rc = -1; continue; } 

其中有个结构体需要注意，每个命令，都有一个名字，还有对应的参数，以及执行命令的函数，这些都被打包放在一起结构体变量中

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 *[]); char *usage; /* Usage message (short) */ #ifdef CFG_LONGHELP char *help; /* Help  message (long) */ #endif #ifdef CONFIG_AUTO_COMPLETE /* do auto completion on the arguments */ int (*complete)(int argc, char *argv[], char last_char, int maxv, char *cmdv[]); #endif }; 

在find_cmd中，通过一个for循环去找命令是否存在

for (cmdtp = &__u_boot_cmd_start;       cmdtp != &__u_boot_cmd_end;       cmdtp++) { if (strncmp (cmd, cmdtp->name, len) == 0) { if (len == strlen (cmdtp->name)) return cmdtp; /* full match */     cmdtp_temp = cmdtp; /* abbreviated command ? */    n_found++; } } 

其中__u_boot_cmd_start和__u_boot_cmd_end是在链接脚本中指定的

. = .;  __u_boot_cmd_start = .; .u_boot_cmd : { *(.u_boot_cmd) }  __u_boot_cmd_end = .; 

再看一下u_boot_cmd这个段到底是干嘛的，可以找到两个宏定义，第一个定义了一个段，第二个在执行命令时进行宏展开

#define Struct_Section  __attribute__ ((unused,section (".u_boot_cmd"))) #define U_BOOT_CMD(name,maxargs,rep,cmd,usage,help)  cmd_tbl_t __u_boot_cmd_##name Struct_Section = {#name, maxargs, rep, cmd, usage, help} 

如果现在执行bootm 0x30007FC0，看看跟宏U_BOOT_CMD有什么关系

U_BOOT_CMD(   bootm, CFG_MAXARGS, 1, do_bootm, "bootm   - boot application image from memoryn", "[addr [arg ...]]n    - boot application image stored in memoryn" "tpassing arguments 'arg ...'; when booting a Linux kernel,n" "t'arg' can be the address of an initrd imagen" #ifdef CONFIG_OF_FLAT_TREE "tWhen booting a Linux kernel which requires a flat device-treen" "ta third argument is required which is the address of the of then" "tdevice-tree blob. To boot that kernel without an initrd image,n" "tuse a '-' for the second argument. If you do not pass a thirdn" "ta bd_info struct will be passed insteadn" #endif ); 

展开后，发现是定义了一个cmd_tbl_t类型的结构体变量__u_boot_cmd_bootm，后面的Struct_Section也宏展开，发现段属性被强制设为u_boot_cmd段

cmd_tbl_t __u_boot_cmd_bootm Struct_Section = {"bootm", CFG_MAXARGS, 1, do_bootm, usage, help} Struct_Section  __attribute__ ((unused,section (".u_boot_cmd"))) 

这里面的usage和help，是替换上面的字符串，其中

• usage：“bootm – boot application image from memoryn”
• help：剩下的所有字符串
  可以发现usage替换的后面是有逗号的，help的字符串双引号之间没有任何间隔符号

接下来自己写一个命令试试看，在common目录下创建文件cmd_hello.c

#include <common.h> #include <watchdog.h> #include <command.h> #include <image.h> #include <malloc.h> #include <zlib.h> #include <bzlib.h> #include <environment.h> #include <asm/byteorder.h> int do_hello (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[]) { printf("hello world uboot sb thingsn"); } U_BOOT_CMD(   hello, CFG_MAXARGS, 1, do_hello, "hello   - this is a first uboot cmd, hello worldn", "this is a infomation for help, long string" ); 

修改command目录下的Makefile文件，增加一个源文件cmd_hello.o，编译烧录即可

uboot启动内核

通过之前的分析，可以知道，内核是由bootm启动，所以接下来分析整个bootcmd命令的参数

s = getenv ("bootcmd"); printf("Booting Linux ...n");             run_command (s, 0); 

这条命令，第一句话，将内核从kernel分区读出，并放到SDRAM的指定地址，然后从这个地址启动内核

bootcmd=nand read.jffs2 0x30007FC0 kernel; bootm 0x30007FC0 

在uboot中，一般会将分区大小写死

#define MTDPARTS_DEFAULT "mtdparts=nandflash0:256k@0(bootloader),"                              "128k(params),"                              "2m(kernel),"                              "-(root)" 

所以第一句话等价于下面的，从0x00060000读取内核，大小为0x00200000，存放到0x30007FC0

bootcmd=nand read.jffs2 0x30007FC0 kernel; bootcmd=nand read.jffs2 0x30007FC0 0x00060000 0x00200000; 

接下来看如何从nand中读取内核，重点在于nand_read_opts

int do_nand(cmd_tbl_t * cmdtp, int flag, int argc, char *argv[]) { ... if (read) { /* read */         nand_read_options_t opts; memset(&opts, 0, sizeof(opts));         opts.buffer = (u_char*) addr;         opts.length = size;         opts.offset = off;         opts.quiet      = quiet;         ret = nand_read_opts(nand, &opts); } ... } 

读出了内核后，接下来如何启动，分析bootm

bootm 0x30007FC0 

首先分析一下uImage的结构，它是一个64字节的头部+真正的内核组成，其中有两项比较重要的参数
ih_load加载地址和ih_ep入口地址

typedef struct image_header { uint32_t ih_magic; /* Image Header Magic Number */ uint32_t ih_hcrc; /* Image Header CRC Checksum */ uint32_t ih_time; /* Image Creation Timestamp */ uint32_t ih_size; /* Image Data Size  */ uint32_t ih_load; /* Data  Load  Address  */ uint32_t ih_ep; /* Entry Point Address  */ uint32_t ih_dcrc; /* Image Data CRC Checksum */ uint8_t  ih_os; /* Operating System  */ uint8_t  ih_arch; /* CPU architecture  */ uint8_t  ih_type; /* Image Type   */ uint8_t  ih_comp; /* Compression Type  */ uint8_t  ih_name[IH_NMLEN]; /* Image Name  */ } image_header_t; 

bootm命令先去读取uImage的头部信息，如果发现当前内核并不位于它指定的加载地址，就将内核移到指定的加载地址，然后uboot需要告诉内核一些启动参数，这些参数是存放到某些地址，然后内核去这些地址去读取对应的参数，就是所谓的tag，参数传完后，跳转到入口地址执行

memmove (&header, (char *)addr, sizeof(image_header_t)); memmove ((void *) ntohl(hdr->ih_load), (uchar *)data, len); do_bootm_linux(...);     setup_start_tag (bd); //设置参数     setup_serial_tag (&params);     setup_revision_tag (&params);     setup_memory_tags (bd);     setup_commandline_tag (bd, commandline);     等等 theKernel = (void (*)(int, int, uint))ntohl(hdr->ih_ep); theKernel (0, bd->bi_arch_number, bd->bi_boot_params); //启动内核 

启动内核时传递了三个参数，其中bd->bi_arch_number是机器ID，bd->bi_boot_params是传递的参数地址