Uboot命令理解与实践

Linux 系统启动需要一个 bootloader 引导加载程序，也就是说芯片上电以后先运行一段bootloader程序。这段bootloader程序会先初始化DDR等外设，然后将Linux内核从flash拷贝到 DDR 中，最后启动 Linux 内核。主要的工作就是启动 Linux 内核， bootloader 和 Linux 内核的关系就跟 PC 上的 BIOS 和 Windows 的关系一样， bootloader 就相当于 BIOS。uboot 的全称是 Universal Boot Loader， uboot 是一个遵循 GPL 协议的开源软件， uboot 是一个裸机代码。

在UBoot命令行中依次测试使用CMD，记录调用过程，整理自己的理解。

命令	含义	理解	图示
?	- alias for ‘help’	help命令的别名，和help功能一致
base	- print or set address offset
bdinfo	- print Board Info structure
boot	- boot default, i.e., run ‘bootcmd’
boot_test	- boot siflower test image	用于启动各种不同类型的测试镜像
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
btn_httpd_detect	- check pmu buttom to run httpd
cmp	- memory compare
coninfo	- print console devices and information
cp	- memory copy
crc32	- checksum calculation
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
exit	- exit script
false	- do nothing, unsuccessfully	输入后没有什么反馈
fdt	- flattened device tree utility commands
go	- start application at address ‘addr’
help	- print command description/usage	和?的作用一样
httpd	- start www server for firmware recovery with [localAddress]		最熟悉不过的httpd 192.168.4.5
iminfo	- print header information for application image
imxtract	- extract a part of a multi-image
itest	- return true/false on integer compare
loop	- infinite loop on address range
lzmadec	- lzma uncompress a memory region
md	- memory display
mm	- memory modify (auto-incrementing address)
mw	- memory write (fill)
nm	- memory modify (constant address)
ping	- send ICMP ECHO_REQUEST to network host	U-Boot 中的 ping 命令主要用于基本的网络测试
printenv	- print environment variables
reset	- Perform RESET of the CPU
rhreset	- Rehold all module resets to save power
run	- run commands in an environment variable
saveenv	- save environment variables to persistent storage
setenv	- set environment variables		用setenv命令在Linux环境中设置环境变量
sf	- SPI flash sub-system
showvar	- print local hushshell variables
sleep	- delay execution for some time
source	- run script from memory
spld	- update spl from device	更新二级启动加载程序
test	- minimal test like /bin/sh
tftpboot	- boot image via network using TFTP protocol
true	- do nothing, successfully	没有什么反馈
version	- print monitor, compiler and linker