（1）UBOOT编译体验

嵌入式系统：
bootloader -->linux内核 --> 挂载根文件系统 --> 应用

一、uboot体验

1、烧写u-boot

uboot体验的时候，我们怎么知道是怎么配置编译的呢，可以查看README文件。

（1）解压缩

（2）打补丁

patch -p1 <../补丁文件

（3）配置

u-boot_1.1.6：make 100ask4x0_config

（4）编译

make

u-boot_1.1.6编译出现warning: target CPU does not support interworking 解决办法：
https://blog.youkuaiyun.com/qq_40674996/article/details/105036704

u-boot_1.1.6编译出现如下错误：

/usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_udivsi3.o): In function `__aeabi_uidiv':
(.text+0x0): multiple definition of `__udivsi3'
lib_arm/libarm.a(_udivsi3.o):/work/u-boot-1.1.6/lib_arm/_udivsi3.S:17: first defined here
arm-linux-ld: ERROR: Source object /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_udivdi3.o) has EABI version 5, but target u-boot has EABI version 0
arm-linux-ld: failed to merge target specific data of file /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_udivdi3.o)
arm-linux-ld: ERROR: Source object /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_udivsi3.o) has EABI version 5, but target u-boot has EABI version 0
arm-linux-ld: failed to merge target specific data of file /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_udivsi3.o)
arm-linux-ld: ERROR: Source object /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_dvmd_lnx.o) has EABI version 5, but target u-boot has EABI version 0
arm-linux-ld: failed to merge target specific data of file /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_dvmd_lnx.o)
arm-linux-ld: ERROR: Source object /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_clz.o) has EABI version 5, but target u-boot has EABI version 0
arm-linux-ld: failed to merge target specific data of file /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_clz.o)
/usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t/libgcc.a(_dvmd_lnx.o): In function `__aeabi_ldiv0':
(.text+0x8): undefined reference to `raise'
Makefile:263: recipe for target 'u-boot' failed
make: *** [u-boot] Error 1

解决方法：将gcc version 4.3.2 换成3.4.5即可
把arm-linux-gcc-3.4.5-glibc-2.3.6.tar.bz2解压到/work/tools目录下
然后修改环境变量vim /etc/environment：
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/arm/4.3.2/bin"
改成
PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/work/tools/gcc-3.4.5-glibc-2.3.6/bin“
然后重启，不重启的话就手动更改：
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/work/tools/gcc-3.4.5-glibc-2.3.6/bin

2、uboot命令

uboot有哪些命令？
输入help
对某个命令的具体解释，如：? md

print 环境变量

二、uboot概述

BIOS怎么启动内核？
从硬盘上读入内核

那么UBOOT怎么启动LINUX内核？
从Flash读出内核，放到SDRAM上，启动内核。

那么uboot需要实现的内容？(基本)
1、读Flash
2、初始化SDRAM
3、启动内核
那么uboot需要实现的内容？(延申)
写Flash ===> 通过网络或者usb把内核写到Flash
1、读Flash
初始化时钟 ===> 因为默认上电是12M晶振
初始化串口 ===> 为了查看信息
2、初始化SDRAM
3、启动内核

总结UBOOT功能：
硬件相关的功能：

• 初始化时钟
• 关闭看门狗
• 初始化SDRAM
• 读Flash

开发板功能：

• 网卡
• usb
• 串口
• 写Flash