一、进入UBoot命令行模式

 上电以后，出现 Hit any key to stop autoboot: 0就按下任意键，出现=>符号就进入命令行模式了，如下：

U-Boot 2016.03 (Dec 12 2020 - 13:19:46 +0800)

CPU:   Freescale i.MX6ULL rev1.1 69 MHz (running at 396 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 48C
Reset cause: POR
Board: MX6ULL 14x14 EVK
I2C:   ready
DRAM:  512 MiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
*** Warning - bad CRC, using default environment

Display: ATK-LCD-4.3-800x480 (800x480)
Video: 800x480x24
In:    serial
Out:   serial
Err:   serial
switch to partitions #0, OK
mmc1(part 0) is current device
Net:   FEC1
Error: FEC1 address not set.

Normal Boot
Hit any key to stop autoboot:  0

二、命令

help命令

=> help
?       - alias for 'help'
base    - print or set address offset
bdinfo  - print Board Info structure
bmode   - sd1|sd2|qspi1|normal|usb|sata|ecspi1:0|ecspi1:1|ecspi1:2|ecspi1:3|esdhc1|esdhc2|esdhc3|esdhc4 [noreset]
bmp     - manipulate BMP image data
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
bootz   - boot Linux zImage image from memory
clocks  - display clocks
cmp     - memory compare
coninfo - print console devices and information
cp      - memory copy
crc32   - checksum calculation
dcache  - enable or disable data cache
dhcp    - boot image via network using DHCP/TFTP protocol
dm      - Driver model low level access
echo    - echo args to console
editenv - edit environment variable
env     - environment handling commands
erase   - erase FLASH memory
exit    - exit script
ext2load- load binary file from a Ext2 filesystem
ext2ls  - list files in a directory (default /)
ext4load- load binary file from a Ext4 filesystem
ext4ls  - list files in a directory (default /)
ext4size- determine a file's size
ext4write- create a file in the root directory
false   - do nothing, unsuccessfully
fatinfo - print information about filesystem
fatload - load binary file from a dos filesystem
fatls   - list files in a directory (default /)
fatsize - determine a file's size
fatwrite- write file into a dos filesystem
fdt     - flattened device tree utility commands
flinfo  - print FLASH memory information
fstype  - Look up a filesystem type
fuse    - Fuse sub-system
go      - start application at address 'addr'
gpio    - query and control gpio pins
help    - print command description/usage
i2c     - I2C sub-system
icache  - enable or disable instruction cache
iminfo  - print header information for application image
imxtract- extract a part of a multi-image
itest   - return true/false on integer compare
load    - load binary file from a filesystem
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
mdio    - MDIO utility commands
mii     - MII utility commands
mm      - memory modify (auto-incrementing address)
mmc     - MMC sub system
mmcinfo - display MMC info
mtest   - simple RAM read/write test
mw      - memory write (fill)
nfs     - boot image via network using NFS protocol
nm      - memory modify (constant address)
ping    - send ICMP ECHO_REQUEST to network host
pmic    - PMIC
printenv- print environment variables
protect - enable or disable FLASH write protection
reset   - Perform RESET of the CPU
run     - run commands in an environment variable
save    - save file to a filesystem
saveenv - save environment variables to persistent storage
setenv  - set environment variables
setexpr - set environment variable as the result of eval expression
sf      - SPI flash sub-system
showvar - print local hushshell variables
size    - determine a file's size
sleep   - delay execution for some time
source  - run script from memory
test    - minimal test like /bin/sh
tftpboot- boot image via network using TFTP protocol
true    - do nothing, successfully
usb     - USB sub-system
usbboot - boot from USB device
version - print monitor, compiler and linker version
=>

 上面的那些命令并不是 uboot 所支持的所有命令，前面说过 uboot 是可配置的，需要什么命令就使能什么命令。所以上面的命令是正点原子提供的 uboot 中使能的命令，uboot 支持的命令还有很多，而且也可以在 uboot 中自定义命令。、

 这些命令后面都跟有命令说明，用于描述此命令的作用，但是命令具体怎么用呢？

 我们输入“help(或?) 命令名”既可以查看命令的详细用法，以“bootz”这个命令为例，我们输入如下命令即可查看“bootz”这个命令的用法：

=> ? bootz
bootz - boot Linux zImage image from memory

Usage:
bootz [addr [initrd[:size]] [fdt]]
    - boot Linux zImage stored in memory
        The argument 'initrd' is optional and specifies the address
        of the initrd in memory. The optional argument ':size' allows
        specifying the size of RAW initrd.
        When booting a Linux kernel which requires a flat device-tree
        a third argument is required which is the address of the
        device-tree blob. To boot that kernel without an initrd image,
        use a '-' for the second argument. If you do not pass a third
        a bd_info struct will be passed instead

信息查询命令

 常用的和信息查询有关的命令有 3 个：

• bdinfo
• printenv
• version

1、bdinfo命令

 先来看一下 bdinfo 命令，此命令用于查看板子信息，直接输入“bdinfo”即可，结果如下：

=> bdinfo
arch_number = 0x00000000
boot_params = 0x80000100
DRAM bank   = 0x00000000
-> start    = 0x80000000
-> size     = 0x20000000
eth0name    = FEC1
ethaddr     = (not set)
current eth = FEC1
ip_addr     = <NULL>
baudrate    = 115200 bps
TLB addr    = 0x9FFF0000
relocaddr   = 0x9FF51000
reloc off   = 0x18751000
irq_sp      = 0x9EF4EEA0
sp start    = 0x9EF4EE90
FB base     = 0x00000000

 从上面中可以得出 DRAM 的起始地址和大小、启动参数保存起始地址、波特率、sp(堆栈指针)起始地址等信息。

2、printenv命令

 命令“printenv”用于输出环境变量信息，uboot 也支持 TAB 键自动补全功能，输入“print”然后按下 TAB 键就会自动补全命令，直接输入“print”也可以。输入“print”，然后按下回车键，环境变量如下面所示：

=> printenv
baudrate=115200
board_name=EVK
board_rev=14X14
boot_fdt=try
bootcmd=run findfdt;mmc dev ${mmcdev};mmc dev ${mmcdev}; if mmc rescan; then if run loadbootscript; then run bootscript; else if run loadimage; then run mmcboot; else run netboot; fi; fi; else run netboot; fi
bootcmd_mfg=run mfgtool_args;bootz ${loadaddr} ${initrd_addr} ${fdt_addr};
bootdelay=1
bootscript=echo Running bootscript from mmc ...; source
console=ttymxc0
ethact=FEC1
ethprime=FEC
fdt_addr=0x83000000
fdt_file=imx6ull-14x14-emmc-4.3-800x480-c.dtb
fdt_high=0xffffffff
findfdt=if test $fdt_file = undefined; then if test $board_name = EVK && test $board_rev = 9X9; then setenv fdt_file imx6ull-9x9-evk.dtb; fi; if test $board_name = EVK && test $board_rev = 14X14; then setenv fdt_file imx6ull-14x14-evk.dtb; fi; if test $fdt_file = undefined; then echo WARNING: Could not determine dtb to use; fi; fi;
image=zImage
initrd_addr=0x83800000
initrd_high=0xffffffff
ip_dyn=yes
loadaddr=0x80800000
loadbootscript=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${script};
loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}
loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}
logo_file=alientek.bmp
mfgtool_args=setenv bootargs console=${console},${baudrate} rdinit=/linuxrc g_mass_storage.stall=0 g_mass_storage.removable=1 g_mass_storage.file=/fat g_mass_storage.ro=1 g_mass_storage.idVendor=0x066F g_mass_storage.idProduct=0x37FF g_mass_storage.iSerialNumber="" clk_ignore_unused
mmcargs=setenv bootargs console=${console},${baudrate} root=${mmcroot}
mmcautodetect=yes
mmcboot=echo Booting from mmc ...; run mmcargs; if test ${boot_fdt} = yes || test ${boot_fdt} = try; then if run loadfdt; then bootz ${loadaddr} - ${fdt_addr}; else if test ${boot_fdt} = try; then bootz; else echo WARN: Cannot load the DT; fi; fi; else bootz; fi;
mmcdev=1
mmcpart=1
mmcroot=/dev/mmcblk1p2 rootwait rw
netargs=setenv bootargs console=${console},${baudrate} root=/dev/nfs ip=dhcp nfsroot=${serverip}:${nfsroot},v3,tcp
netboot=echo Booting from net ...; run netargs; if test ${ip_dyn} = yes; then setenv get_cmd dhcp; else setenv get_cmd tftp; fi; ${get_cmd} ${image}; if test ${boot_fdt} = yes || test ${boot_fdt} = try; then if ${get_cmd} ${fdt_addr} ${fdt_file}; then bootz ${loadaddr} - ${fdt_addr}; else if test ${boot_fdt} = try; then bootz; else echo WARN: Cannot load the DT; fi; fi; else bootz; fi;
panel=ATK-LCD-4.3-800x480
script=boot.scr
splashimage=0x88000000
splashpos=m,m

Environment size: 2536/8188 bytes

 有很多的环境变量，比如 baudrate、board_name、board_rec、boot_fdt、bootcmd等等。uboot 中的环境变量都是字符串，既然叫做环境变量，那么它的作用就和“变量”一样。

 比如 bootdelay 这个环境变量就表示 uboot 启动延时时间，默认bootdelay=3，也就默认延时 3秒。前面说的 3 秒倒计时就是由 bootdelay 定义的，如果将 bootdelay 改为 5 的话就会倒计时 5s了。uboot 中的环境变量是可以修改的，有专门的命令来修改环境变量的值。

3、version命令

 命令 version 用于查看 uboot 的版本号，输入“version”，uboot 版本号如下所示：

=> version

U-Boot 2016.03 (Dec 12 2020 - 13:19:46 +0800)
arm-linux-gnueabihf-gcc (Linaro GCC 4.9-2017.01) 4.9.4
GNU ld (Linaro_Binutils-2017.01) 2.24.0.20141017 Linaro 2014_11-3-git

环境变量操作命令

1、修改环境变量

 环境变量的操作涉及到两个命令：

• setenv ：用于设置或者修改环境变量的值
• saveenv：用于保存修改后的环境变量，一般环境变量是存放在外部 flash 中的，uboot 启动的时候会将环境变量从 flash 读取到 DRAM 中。所以使用命令 setenv 修改的是 DRAM中的环境变量值，修改以后要使用 saveenv 命令将修改后的环境变量保存到 flash 中，否则的话uboot 下一次重启会继续使用以前的环境变量值。

使用格式

比如我们要将环境变量 bootdelay 改为 5，就可以使用如下所示命令：

setenv bootdelay 5
saveenv

如下：

=> setenv bootdelay 5
=> saveenv
Saving Environment to MMC...
Writing to MMC(1)... done

 当我们使用命令 saveenv 保存修改后的环境变量的话会有保存过程提示信息，根据提示可以看出环境变量保存到了 MMC(1)中，也就是 EMMC 中。因为我用的 EMMC版本的核心板，所以会保存到MMC(1)中，如果是NAND版本核心板的话就会提示保存到NAND中。

 修改 bootdelay 以后，重启开发板，uboot 就是变为 5 秒倒计时:

=> setenv bootdelay 5
=> saveenv
Saving Environment to MMC...
Writing to MMC(1)... done
=> reset
resetting ...


U-Boot 2016.03 (Dec 12 2020 - 13:19:46 +0800)

CPU:   Freescale i.MX6ULL rev1.1 69 MHz (running at 396 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 57C
Reset cause: WDOG
Board: MX6ULL 14x14 EVK
I2C:   ready
DRAM:  512 MiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
Display: ATK-LCD-4.3-800x480 (800x480)
Video: 800x480x24
In:    serial
Out:   serial
Err:   serial
switch to partitions #0, OK
mmc1(part 0) is current device
Net:   FEC1
Error: FEC1 address not set.

Normal Boot
Hit any key to stop autoboot:  5

 有时候我们修改的环境变量值可能会有空格，比如 bootcmd、bootargs 等，这个时候环境变量值就得用单引号括起来，比如下面修改环境变量 bootargs 的值：

setenv bootargs 'console=ttymxc0,115200 root=/dev/mmcblk1p2 rootwait rw'
saveenv

 上面命令设置 bootargs 的值为“console=ttymxc0,115200 root=/dev/mmcblk1p2 rootwait rw”，其中“console=ttymxc0,115200”、“root=/dev/mmcblk1p2”、“rootwait”和“rw”相当于四组“值”，这四组“值”之间用空格隔开，所以需要使用单引号‘’将其括起来，表示这四组“值”都属于环境变量 bootargs。

2、新建环境变量

 命令 setenv 也可以用于新建命令，用法就是修改环境变量一样，比如我们新建一个环境变量 author，author 的值为我的名字音：liefyuan，那么就可以使用如下命令：

setenv author liefyuan
saveenv

author 完成以后重启 uboot，然后使用命令 printenv 查看当前环境变量：

=> setenv author liefyuan
=> saveenv
Saving Environment to MMC...
Writing to MMC(1)... done
=> reset
resetting ...


U-Boot 2016.03 (Dec 12 2020 - 13:19:46 +0800)

CPU:   Freescale i.MX6ULL rev1.1 69 MHz (running at 396 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 57C
Reset cause: WDOG
Board: MX6ULL 14x14 EVK
I2C:   ready
DRAM:  512 MiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
Display: ATK-LCD-4.3-800x480 (800x480)
Video: 800x480x24
In:    serial
Out:   serial
Err:   serial
switch to partitions #0, OK
mmc1(part 0) is current device
Net:   FEC1
Error: FEC1 address not set.

Normal Boot
Hit any key to stop autoboot:  0
=> print
author=liefyuan
baudrate=115200
board_name=EVK
board_rev=14X14
...

3、删除环境变量

 既然可以新建环境变量，那么就可以删除环境变量，删除环境变量也是使用命令 setenv，要删除一个环境变量只要给这个环境变量赋空值即可，比如我们删除掉上面新建的 author 这个环境变量，命令如下：

setenv author
saveenv

 上面命令中通过 setenv 给 author 赋空值，也就是什么都不写来删除环境变量 author。重启uboot 就会发现环境变量 author 没有了:

=> setenv author
=> saveenv
Saving Environment to MMC...
Writing to MMC(1)... done
=> reset
resetting ...


U-Boot 2016.03 (Dec 12 2020 - 13:19:46 +0800)

CPU:   Freescale i.MX6ULL rev1.1 69 MHz (running at 396 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 57C
Reset cause: WDOG
Board: MX6ULL 14x14 EVK
I2C:   ready
DRAM:  512 MiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
Display: ATK-LCD-4.3-800x480 (800x480)
Video: 800x480x24
In:    serial
Out:   serial
Err:   serial
switch to partitions #0, OK
mmc1(part 0) is current device
Net:   FEC1
Error: FEC1 address not set.

Normal Boot
Hit any key to stop autoboot:  0
=> print
baudrate=115200
board_name=EVK
board_rev=14X14

内存操作命令