【记录】u-boot中添加命令

1. 添加命令

目标：在u-boot中添加一条命令，执行命令后打印出hello world和参数信息。

新建cmd_hello.c，放到common目录下。

#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[])
{
    char i;

    printf ("## hello world! %d\n", argc);

    for(i = 0; i < argc; i++){
        printf("argv[%d]: %s\n", i, argv[i]);
    }

    return 0;
}


U_BOOT_CMD(
    hello,  CFG_MAXARGS,    1,  do_hello,
    "hello - usage.\n",
    "hello - long help..............\n"
);

2. 修改Makefile

修改common目录下的Makefile

vi common/Makefile

COBJS后面追加cmd_hello.o

3. 重新编译

make
…
arm-linux-objcopy –gap-fill=0xff -O binary u-boot u-boot.bin

4. 下载测试

下载后，串口测试

##### 100ask Bootloader for OpenJTAG #####
[n] Download u-boot to Nand Flash
[k] Download Linux kernel uImage
[j] Download root_jffs2 image
[y] Download root_yaffs image
[d] Download to SDRAM & Run
[z] Download zImage into RAM
[g] Boot linux from RAM
[f] Format the Nand Flash
[s] Set the boot parameters
[b] Boot the system
[r] Reboot u-boot
[q] Quit from menu
Enter your selection: q
OpenJTAG> 
OpenJTAG> help
?       - alias for 'help'
autoscr - run script from memory
base    - print or set address offset
bdinfo  - print Board Info structure
boot    - boot default, i.e., run 'bootcmd'
bootd   - boot default, i.e., run 'bootcmd'
bootelf - Boot from an ELF image in memory
bootm   - boot application image from memory
bootp   - boot image via network using BootP/TFTP protocol
bootvx  - Boot vxWorks from an ELF image
chpart  - change active partition
cmp     - memory compare
coninfo - print console devices and information
cp      - memory copy
crc32   - checksum calculation
date    - get/set/reset date & time
dcache  - enable or disable data cache
echo    - echo args to console
erase   - erase FLASH memory
flinfo  - print FLASH memory information
fsinfo  - print information about filesystems
fsload  - load binary file from a filesystem image
go      - start application at address 'addr'
hello - usage.
help    - print online help
icache  - enable or disable instruction cache
iminfo  - print header information for application image
imls    - list all images found in flash
itest   - return true/false on integer compare
loadb   - load binary file over serial line (kermit mode)
loads   - load S-Record file over serial line
loadx   - load binary file over serial line (xmodem mode)
loady   - load binary file over serial line (ymodem mode)
loop    - infinite loop on address range
ls      - list files in a directory (default /)
md      - memory display
menu - display a menu, to select the items to do something
mm      - memory modify (auto-incrementing)
mtdparts- define flash/nand partitions
mtest   - simple RAM test
mw      - memory write (fill)
nand    - NAND sub-system
nboot   - boot from NAND device
nfs     - boot image via network using NFS protocol
nm      - memory modify (constant address)
ping    - send ICMP ECHO_REQUEST to network host
printenv- print environment variables
protect - enable or disable FLASH write protection
rarpboot- boot image via network using RARP/TFTP protocol
reset   - Perform RESET of the CPU
run     - run commands in an environment variable
saveenv - save environment variables to persistent storage
setenv  - set environment variables
sleep   - delay execution for some time
tftpboot- boot image via network using TFTP protocol
usbslave - get file from host(PC)
version - print monitor version

OpenJTAG> help hello
hello hello - long help..............

OpenJTAG> hello abc def
## hello world! 3
argv[0]: hello
argv[1]: abc
argv[2]: def
OpenJTAG> 

5. 分析

u-boot命令格式(Command.h)

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
};

查找命令（Command.c）

cmd_tbl_t *find_cmd (const char *cmd)
{
    cmd_tbl_t *cmdtp;
    cmd_tbl_t *cmdtp_temp = &__u_boot_cmd_start;    /*Init value */
    const char *p;
    int len;
    int n_found = 0;

    /*
     * Some commands allow length modifiers (like "cp.b");
     * compare command name only until first dot.
     */
    len = ((p = strchr(cmd, '.')) == NULL) ? strlen (cmd) : (p - cmd);

    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++;
        }
    }
    if (n_found == 1) {         /* exactly one match */
        return cmdtp_temp;
    }

    return NULL;    /* not found or ambiguous command */
}

查找命令并没有像我们想象的那样是一个数组，而是通过__u_boot_cmd_start，__u_boot_cmd_end来查找，查看连接脚本。
连接脚本中的内容(\board\100ask24x0\u-boot.lds)

OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
/*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/
OUTPUT_ARCH(arm)
ENTRY(_start)
SECTIONS
{
    . = 0x00000000;

    . = ALIGN(4);
    .text      :
    {
      cpu/arm920t/start.o   (.text)
          board/100ask24x0/boot_init.o (.text)
      *(.text)
    }

    . = ALIGN(4);
    .rodata : { *(.rodata) }

    . = ALIGN(4);
    .data : { *(.data) }

    . = ALIGN(4);
    .got : { *(.got) }

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

    . = ALIGN(4);
    __bss_start = .;
    .bss : { *(.bss) }
    _end = .;
}

U_BOOT_CMD定义(Command.h)

#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}

到这里我们就明白了。在定义u-boot命令时，所有使用宏U_BOOT_CMD定义的命令会被链接到指定的段（起始地址：__u_boot_cmd_start；结束地址：__u_boot_cmd_end），查找命令时，使用它们来判断命令是否存在。