Linux嵌入式uboot使用tftp网络启动加载zImage、设备树

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一、前言

先来讲一下为什么要使用tftp网络启动加载zImage和设备树。

在做驱动开发学习的时候，我们每次涉及到一个学习目标，比如学习led灯设备驱动开发，我们需要去设备树中添加节点，然后进行编译，编译好之后需要将我们的设备树和zImage文件上传到开发板，替换掉开发板上面相对应的文件，然后进行sudo reboot重新启动。

所以为了方便，可以使用Linux嵌入式uboot使用tftp网络启动加载zImage、设备树。也就是每次开启的时候，会从我们虚拟机tftpboot路径下去寻找我们的zImage和设备树启动，就不需要每次都下载然后重新reboot了。

如何搭建tftp服务器可以参考这篇文章：wpa_supplicant无线网络配置imx6ull以及搭建tftp服务器

在重启开发板的时候，随意按键即可进入u-boot模式。

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二、Linux U-boot 相关命令

• help： printenv命令描述/用法
• printenv： 打印环境变量
• setenv： 设置环境变量
• saveenv： 将环境变量保存到持久存储

接下来我们详细讲解这几个命令。

（1）help 命令

可用于察看当前开发板所支持的命令。

[u-boot@igkboard]# help 
?         - alias for 'help'
base      - print or set address offset
bdinfo    - print Board Info structure
blkcache  - block cache diagnostics and control
bmode     - sd1|sd2|qspi1|normal|usb|sata|ecspi1:0|ecspi1:1|ecspi1:2|ecspi1:3|esdhc1|esdhc2|esdhc3|esdhc4
bmode - getprisec
bmp       - manipulate BMP image data
boot      - boot default, i.e., run 'bootcmd'
bootd     - boot default, i.e., run 'bootcmd'
bootefi   - Boots an EFI payload from memory
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
fastboot  - run as a fastboot usb or udp device
fatinfo   - print information about filesystem
fatload   - load binary file from a dos filesystem
fatls     - list files in a directory (default /)
fatmkdir  - create a directory
fatrm     - delete a file
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
fstypes   - List supported filesystem types
fuse      - Fuse sub-system
go        - start application at address 'addr'
gpio      - query and control gpio pins
gpt       - GUID Partition Table
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
lcdputs   - print string on video framebuffer
ln        - Create a symbolic link
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
mm        - memory modify (auto-incrementing address)
mmc       - MMC sub system
mmcinfo   - display MMC info
mtest     - simple RAM read/write test
mw        - memory write (fill)
net       - NET sub-system
nfs       - boot image via network using NFS protocol
nm        - memory modify (constant address)
panic     - Panic with optional message
ping      - send ICMP ECHO_REQUEST to network host
pinmux    - show pin-controller muxing
printenv  - print environment variables
protect   - enable or disable FLASH write protection
qspihdr   - Q(F)SPI Boot Config sub-system
random    - fill memory with random pattern
read      - Load binary data from a partition
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
setcurs   - set cursor position within screen
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
ums       - Use the UMS [USB Mass Storage]
usb       - USB sub-system
usbboot   - boot from USB device
version   - print monitor, compiler and linker version
videolink - list and select video link

（2）printenv 命令

printenv 命令查看环境变量也可以使用缩写：print

[u-boot@igkboard]# printenv    
author=weihuihong
baudrate=115200
bbl=tftp ${loadaddr} u-boot-igkboard.imx && mmc dev ${mmcdev} 1 && mmc write ${loadaddr} 2 0x500
bdtb=tftp $fdt_addr $fdt_file && fatwrite mmc 1:1 $fdt_addr $fdt_file $filesize
bker=tftp $loadaddr $image&& fatwrite mmc 1:1 $loadaddr $image $filesize
board_name=EVK
board_rev=14X14
bootcmd=run mmcbootdto
bootdelay=3
bsys=run bdtb && run bker
console=ttymxc0
dtbo_addr=0x83010000
dtbo_dir=overlays
emmc_ack=1
emmc_dev=1
env_conf=config.txt
eth1addr=be:19:97:40:6d:ff
ethact=ethernet@20b4000
ethaddr=3e:0a:c4:12:ae:e2
ethprime=eth1
fastboot_dev=mmc1
fdt_addr=0x83000000
fdt_file=igkboard.dtb
fdt_size=0x10000
fdtcontroladdr=9de744c0
image=zImage
ipaddr=192.168.137.213
loadaddr=0x80800000
loadenvconf=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${env_conf};env import -t ${loadaddr} ${filesize}
loadfdt=fatload mmc ${mmcdev}:${mmcpart} ${fdt_addr} ${fdt_file}
loadimage=fatload mmc ${mmcdev}:${mmcpart} ${loadaddr} ${image}
mmc_no=1
mmcargs=setenv bootargs console=${console},${baudrate} root=/dev/mmcblk${mmc_no}p2 rootwait rw net.ifnames=0
mmcboot=echo Booting from mmc ...; mmc dev ${mmcdev}; run mmcargs; run loadenvconf;run loadimage; run loadfdt; bootz ${loadaddr} - ${fdt_addr}
mmcbootdto=echo Booting from mmc with overlay...; mmc dev ${mmcdev}; run mmcargs; run loadenvconf; run loadimage; run loadfdt; if env exists dtoverlay_lcd && test ${dtoverlay_lcd} = 1 -o ${dtoverlay_lcd} = yes ; then setenv dtbo_file lcd.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr}; fi; if env exists dtoverlay_cam && test ${dtoverlay_cam} = 1 -o ${dtoverlay_cam} = yes ; then setenv dtbo_file cam.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr}; fi; if env exists dtoverlay_i2c1 && test ${dtoverlay_i2c1} = 1 -o ${dtoverlay_i2c1} = yes ; then setenv dtbo_file i2c1.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr}; fi; if env exists dtoverlay_spi1 && test ${dtoverlay_spi1} = 1 -o ${dtoverlay_spi1} = yes ; then setenv dtbo_file spi1.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr}; fi; if env exists dtoverlay_uart; then for i in ${dtoverlay_uart}; do setenv dtbo_file uart$i.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr};  done;fi; if env exists dtoverlay_can; then for i in ${dtoverlay_can}; do setenv dtbo_file can$i.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr};  done;fi; if env exists dtoverlay_pwm; then for i in ${dtoverlay_pwm}; do setenv dtbo_file pwm$i.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr};  done;fi; if env exists dtoverlay_extra; then for f in ${dtoverlay_extra}; do setenv dtbo_file $f.dtbo; echo Applying DT overlay ==> ${dtbo_file}; fatload mmc ${mmcdev}:${mmcpart} ${dtbo_addr} ${dtbo_dir}/${dtbo_file}; fdt addr ${fdt_addr}; fdt resize ${fdt_size}; fdt apply ${dtbo_addr};  done;fi; bootz ${loadaddr} - ${fdt_addr}
mmcdev=1
mmcpart=1
netboot=echo Booting from net ...; tftp $loadaddr $image; tftp $fdt_addr ${fdt_file};run mmcargs; bootz ${loadaddr} - ${fdt_addr}
serial#=303769d759a6d668
serverip=192.168.137.91
splashimage=0x8c000000
tee=no
upmode=fastboot 0Environment size: 4012/8188 bytes

里面的内容也是学长之前写好的或者添加的，直接拿来用就可。

也可以查看某一个环境变量的值：

[u-boot@igkboard]# printenv serverip
serverip=192.168.137.91

（3）setenv 函数

setenv name value 添加/修改环境变量：

[u-boot@igkboard]# setenv serverip 192.168.137.99

修改后：

setenv name 删除环境变量：

[u-boot@igkboard]# setenv serverip

修改后：

（4）saveenv 函数

保存环境变量，将当前定义的所有变量及其值存入flash中。

[u-boot@igkboard]# saveenv
Saving Environment to MMC... Writing to MMC(1)... OK

当设置完环境变量之后，如果执行了saveenv的话，则下次重新运行的时候环境变量则会被保存为上次保存的值；如果不保存，只会在设置好时还没重启之前生效，重启之后设置值会恢复成原来的值。

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三、tftp启动linux内核步骤

（1）进入u-boot模式

开始启动的时候在倒数三秒时间按随机键进入到u-boot模式：

Hit any key to stop autoboot:  0 
[u-boot@igkboard]# 

（2）ping通主机

查看是否ping通tftp所在服务器主机：

[u-boot@igkboard]# ping 192.168.137.91
Using ethernet@20b4000 device
host 192.168.137.91 is alive

提示 xxx alive说明成功，可以ping通。

（3）修改IP

需要修改环境变量中的主机IP和服务器IP，注意，一般服务器IP都是不会变的，主机IP会变，但是主机IP需要在一个网段内就可，不需要每次都去修改的。

[u-boot@igkboard]# setenv ipaddr 192.168.137.99
[u-boot@igkboard]# setenv serverip 192.168.137.91
[u-boot@igkboard]# print ipaddr
ipaddr=192.168.137.99
[u-boot@igkboard]# print serverip
serverip=192.168.137.91

然后我们需要保存一下saveenv

（4）从网络启动

执行命令run netboot

[u-boot@igkboard]# run netboot
Booting from net ...
Using ethernet@20b4000 device
TFTP from server 192.168.137.91; our IP address is 192.168.137.99
Filename 'zImage'.
Load address: 0x80800000
Loading: #####################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################1.4 MiB/s
done
Bytes transferred = 9466232 (907178 hex)
Using ethernet@20b4000 device
TFTP from server 192.168.137.91; our IP address is 192.168.137.99
Filename 'igkboard.dtb'.
Load address: 0x83000000
Loading: ####1.1 MiB/s
done

说明成功了。

具体实现的代码在配置中写了，但是还不是很清楚，后面学到再补充。

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