一.官方环境变量bootcmd
bootcmd变量定义位于“include/configs/mx6ull_my_evk.h”(copy from include/configs/mx6ullevk.h )中,
#define CONFIG_BOOTCOMMAND \
"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"
#endif
此脚本主要做四件事,
a.MMC设备查找。
b.读取zImage
c.驱动设备树
d.启动Linux.
不做分析,删除,按照我们需求改写如下
#define CONFIG_BOOTCOMMAND \
"mmc dev 1;" \
"fatload mmc 1:1 0x80800000 zImage;" \
"fatload mmc 1:1 0x83000000 imx6ull_my_evk.dtb;" \
"bootz 0x80800000-0x83000000;"
#endif
修改后重启,发现该环境变量并没有生效
![在这里插入图片描述](https://img-blog.csdnimg.cn/20200513202703589.png)
这是因为源码中,启动时会对环境变量进行检测,如果不为空,则不更新。
我们可以在uboot使用env命令对bootargs变量恢复默认值。
=> env help
env - environment handling commands
Usage:
env default [-f] -a - [forcibly] reset default environment
env default [-f] var [...] - [forcibly] reset variable(s) to their default values
env delete [-f] var [...] - [forcibly] delete variable(s)
env edit name - edit environment variable
env exists name - tests for existence of variable
env export [-t | -b | -c] [-s size] addr [var ...] - export environment
env import [-d] [-t [-r] | -b | -c] addr [size] - import environment
env print [-a | name ...] - print environment
env run var [...] - run commands in an environment variable
env save - save environment
env set [-f] name [arg ...]
对某一变量恢复,使用
env default [-f] var [...] - [forcibly] reset variable(s) to their default values
对所有变量恢复,使用命令
env default [-f] -a - [forcibly] reset default environment
运行结果:
![在这里插入图片描述](https://img-blog.csdnimg.cn/20200513212051308.png)
可以看到变量已经恢复。
二.官方环境变量bootargs.
bootargs由第145-147行脚本设置而来。展开后为
mmcargs=setenv bootargs console= ttymxc0, 115200 root= /dev/mmcblk1p2 rootwait rw
![在这里插入图片描述](https://img-blog.csdnimg.cn/20200512203445638.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xvdmVzaGlwdGluZw==,size_16,color_FFFFFF,t_70)
此环境变量根据自身环境决定是否需要修改。
本文内容由网友自发贡献,版权归原作者所有,本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容,请联系:hwhale#tublm.com(使用前将#替换为@)