可以通过mtd方式读取，也可以用ioremap方式。不过这些都比较麻烦，简单的方法有两种，一种是mtd_debug，另一种是fw_printenv。前者是一个软件包，需要单独下载安装。后一个就是我目前使用的方式，是Uboot带的一个工具，使用方法如下：



1、编译fw_printenv工具


在你uboot目录下用以下编译指令：
make env

成功后在tools/env下会生成fw_printenv，如果提示缺少mtd-user.h文件，从系统中拷贝过来即可：
cp /usr/include/mtd/ ./include/mtd -a


2、修改配置文件


根据mtd分区、UBOOT环境变量的位置、大小等内容修改tools/env下的fw_env.config文件，可参见/tools/env/README文件。

这 个工具还需要一个配置文件，以获取uboot的ENV区域的位置信息。默认状态下，请将fw_env.config文件拷贝到目标机的文件系统的/etc 目录下。然后结合uboot配置中定义的ENV区和Linux下mtd分区的情况修改配置文件。具体的修改方法见fw_env.config文件中的说明 及/tools/env/README文件。

3、使用fw_printenv工具


将编译好的fw_printenv拷贝到目标机的文件系统中，并将fw_env.config文件拷贝到目标机的文件系统的/etc 目录下。执行fw_printenv即可打印Uboot环境变量信息，如果没打印出来或者打印乱码，请检查配置文件是否正确


 


转载：http://labs.isee.biz/index.php/How_to_modify_the_uboot_environment_from_userspace


 



How to modify the uboot environment from userspace



Contents

[hide]

  • ​



Overview

This How-To is meant to be a starting point for people to learn how access to the uboot environment from userspace.

This is my first wiki page so please be benevolent with the formatting :-)


Tools needed

In order to modify the uboot environment variables from userspace we will need a program called fw_setenv, we can compile this program ourselves from the u-boot sources, follow the instructions in this wiki page and then proceed to compile with (don't modify the .h file as it says in the tools/env/README file):

make env


This will give us fw_printenv, in order to get fw_setenv we just have to change the name of the file. Magic!!

cp fw_printenv fw_setenv


The next thing we will need is the fw_env.config file with the appropiate settings for our board. Here comes the confusion :-)

In this file you have to specify:

  2. MTD device name
  3. Device Offset
  4. Environment Size
  5. Flash sector size
  6. Number of sectors (ignored in NOR)



Finding out the correct values for fw_env.config

Ok, so in order to get all this information the easyest thing is to read it from dmesg or from /proc/mtd 

cat /proc/mtd


All my initial confusion comes from using an incorrect kernel, my first tries where with 2.6.28.10 and the driver used to read mtd was NAND, in the kernel configuration file I only had :

CONFIG_MTD_NAND=y


being the output of /proc/mtd:


dev:    size   erasesize  name 
mtd0: 00080000 00040000 "X-Loader"
mtd1: 001e0000 00040000 "U-Boot"
mtd2: 00020000 00040000 "U-Boot Env"
mtd3: 00500000 00040000 "Kernel"
mtd4: 1f880000 00040000 "File System"


through "dmesg" I could see this line indicating something was wrong: 


[ 1174.517120] Creating 5 MTD partitions on "omap2-onenand":
[ 1174.522552] 0x00000000-0x00080000 : "X-Loader"
[ 1174.528381] 0x00080000-0x00260000 : "U-Boot"
[ 1174.533508] 0x00260000-0x00280000 : "U-Boot Env"
[ 1174.538177] mtd: partition "U-Boot Env" doesn't start on an erase block boundary -- force read-only
[ 1174.548126] 0x00280000-0x00780000 : "Kernel"
[ 1174.553192] 0x00780000-0x20000000 : "File System"


But if we use the aproppiate kernel, in my case 2.6.33.7-0 with the onenand driver instead of the nand driver:

CONFIG_MTD_ONENAND=y


The output of /proc/mtd is different:


dev:    size   erasesize  name
mtd0: 00080000 00040000 "X-Loader"
mtd1: 00180000 00040000 "U-Boot"
mtd2: 00080000 00040000 "Environment"
mtd3: 00300000 00040000 "Kernel"
mtd4: 1fa80000 00040000 "File System"


Now we can fill in all the values we needed (that's what I thought)

  2. MTD device name ---> /dev/mtd2 ("u-boot environment")
  3. Device Offset ----> 80.000 + 18.000
  4. Environment Size ---> 80.000
  5. Flash sector size ---> 40.000
  6. Number of sectors (ignored in NOR)----> nothing

Pretty easy right? wrong!!! The right values are:


  2. MTD device name ----> /dev/mtd2
  3. Device Offset -----> 0x0000
  4. Environment Size -----> 0x01000
  5. Flash sector size ------> 0x020000
  6. Number of sectors (ignored in NOR) -----> nothing

I figured these out by reading different posts and by trial and error, but I still don't understand the environment size value or the flash sector size, I can imagine the device offset is 0 if you specify /dev/mtd2 but I'd be great if someone could edit this page and point out why are this the correct values.


Giving it a try

In order to give it a try is better to poke with fw_printenv than with fw_setenv, because the first one just tries to read, so go ahead and try it: 

fw_printenv


this should output something like:

ethact=smc911x-0
distro=poky
project=poky-image-sato
ipaddr=192.168.254.254
netmask=255.255.255.0
gatewayip=192.168.254.10
serverip=192.168.254.10
addip=setenv bootargs ${bootargs} ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}::eth0:
mmc-boot=mmc init 0; if fatload mmc 0 80000000 boot.ini; then source; else if fatload mmc 0 80000000 uImage; then run mmc-bootargs; bootm; fi; fi
onenand-bootargs=setenv bootargs ${bootargs-base} root=/dev/mtdblock4 rootfstype=jffs2 ; run addip
onenand-boot=run onenand-bootargs; onenand read 80000000 280000 400000 ; bootm 80000000
nfs-bootargs=setenv bootargs ${bootargs-base} root=/dev/nfs nfsroot=${serverip}:/srv/nfs/${distro}/${project}/${machine} ; run addip
nfs-boot=if ping ${serverip}; then run nfs-bootargs; tftp 0x80000000 ${distro}/${project}/${machine}/uImage; bootm; fi;
machine=igep0020
mmc-bootargs=setenv bootargs ${bootargs-base} root=/dev/mmcblk0p2 rw rootwait dieid=${dieid#}
dieid#=638a00040000000004036abc07016018
mpurate=110
stdin=serial
stdout=serial
stderr=serial
bootargs-base=mem=512M console=ttyS2,115200n8 console=tty0 omapfb.mode=dvi:1024x768MR-16@60 mpurate=110
bootcmd=run onenand-boot; run mmc-boot;


if you get something like:

Warning: Bad CRC, using default environment
bootcmd=bootp; setenv bootargs root=/dev/nfs nfsroot=${serverip}:${rootpath} ip=${ipaddr}:${serverip}:${gatewayip}:${netmask}:${hostname}::off; bootm
bootdelay=5
baudrate=115200


it means the values in /etc/fw_env.config are not correct, so don't even try fw_setenv



Using fw_setenv

Now that we found out the correct values for /etc/fw_env.config you can just use fw_setenv with the same syntax as if you were in u-boot command line, to assing a value don't use "=" but a space. 

./fw_setenv test 1234


then fw_printenv should output

test=1234


notice we didn't need to use saveenv as we would do in u-boot command line.

That's it!!


 

转载:http://www.denx.de/wiki/DULG/HowCanIAccessUBootEnvironmentVariablesInLinux

 

Question: I would like to access U-Boot's environment variables from my Linux application. Is this possible?

 

Answer: Yes, you can. The environment variables must be stored in flash memory, and your Linux kernel must support flash access through the ​​MTD​​ layer. In the U-Boot source tree you can find the environment tools in the directory ​​tools/env​​, which can be built with command:

 

make env


For building against older versions of the ​​MTD​​ headers (meaning before v2.6.8-rc1) it is required to pass the argument "MTD_VERSION=old" to make:

 

make MTD_VERSION=old env


The resulting binary is called ​​fw_printenv​​, but actually includes support for setting environment variables too. To achieve this, the binary behaves according to the name it is invoked as, so you will have to create a link called ​​fw_setenv​​ to ​​fw_printenv​​.

These tools work exactly like the U-Boot commands ​​printenv​​ resp. ​​setenv​​ You can either build these tools with a fixed configuration selected at compile time, or you can configure the tools using the ​​/etc/fw_env.config​​ configuration file in your target root filesystem. Here is an example configuration file:

 

# Configuration file for fw_(printenv/setenv) utility.
# Up to two entries are valid, in this case the redundant
# environment sector is assumed present.

#########################################################################
# For TQM8xxL modules:
#########################################################################
# MTD device name       Device offset   Env. size       Flash sector size
/dev/mtd0            0x8000          0x4000          0x4000
/dev/mtd0            0xC000          0x4000          0x4000

#########################################################################
# For NSCU:
#########################################################################
# MTD device name       Device offset   Env. size       Flash sector size
#/dev/mtd1              0x0000          0x8000          0x20000
#/dev/mtd2              0x0000          0x8000          0x20000


#########################################################################
# For LWMON
#########################################################################
# MTD device name       Device offset   Env. size       Flash sector size
#/dev/mtd1               0x0000          0x2000          0x40000


转载：http://blog.csdn.net/hangbing0203/article/details/4314576

 

u-boot在线更新
需编译mtd-utils，编译fw_printenv、fw_setenv， 和修改内核
1.编译mtd-utils
将编译的flash_eraseall、flashcp拷贝到/nfsroot/cq8401/sbin中
然后用命令
flash_eraseall /dev/mtd1 刷bootloader分区
用命令
flashcp /bootloader/u-boot.bin.336new  /dev/mtd1  将新的u-boot写入u-boot分区
2.编译fw_printenv和fw_setenv
进入u-boot-1.1.3/
vi tools/env/Makefile
加入
CROSS_COMPILE = mipsel-linux-
make -C tools/env all
cp  tools/env/fw_printenv  /nfsroot/cq8401/sbin
cd /nfsroot/cq8401/sbin
ln -sf fw_printenv fw_setenv
cp -av u-boot-1.1.3/tools/env/fw_env.config /nfsroot/cq8401/etc
问题汇总：
问题1:
fw_env.c:34:27: 错误：linux/mtd/mtd.h：没有那个文件或目录
fw_env.c: 在函数‘fw_printenv’中:
fw_env.c:244: 警告：初始化指针时目标与指针符号不一致
fw_env.c:259: 警告：传递‘fputs’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:262: 警告：传递‘puts’的参数 1 给指针时，目标与指针符号不一致
fw_env.c: 在函数‘fw_setenv’中:
fw_env.c:293: 警告：对指针赋值时目标与指针符号不一致
fw_env.c:317: 警告：传递‘strcmp’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:318: 警告：传递‘strcmp’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:350: 警告：传递‘strlen’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:364: 警告：初始化指针时目标与指针符号不一致
fw_env.c: 在函数‘flash_io’中:
fw_env.c:390: 错误：‘erase_info_t’未声明(在此函数内第一次使用)
fw_env.c:390: 错误：(即使在一个函数内多次出现，每个未声明的标识符在其
fw_env.c:390: 错误：所在的函数内也只报告一次。)
fw_env.c:390: 错误：expected ‘;’ before ‘erase’
fw_env.c:393: 警告：传递‘open’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:409: 警告：传递‘open’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:421: 错误：‘erase’未声明(在此函数内第一次使用)
fw_env.c:423: 错误：‘MEMUNLOCK’未声明(在此函数内第一次使用)
fw_env.c:462: 错误：‘MEMERASE’未声明(在此函数内第一次使用)
fw_env.c:519: 错误：‘MEMLOCK’未声明(在此函数内第一次使用)
fw_env.c: 在函数‘parse_config’中:
fw_env.c:719: 警告：传递‘stat’的参数 1 给指针时，目标与指针符号不一致
fw_env.c:726: 警告：传递‘stat’的参数 1 给指针时，目标与指针符号不一致
make: *** [fw_printenv] 错误 1
解决办法：
在tools/env/Makefile
加入CROSS_COMPILE = mipsel-linux-
问题2：
Cannot parse config file: No such file or directory
解决办法：
在/etc下创建fw_env.config文件
问题3：
Cannot parse config file: Invalid argument
解决办法：
修改文件权限
问题4：
Bus error
解决办法：
echo "/dev/mtd2       0x0000      0x20000      0x20000" > /etc/fw_env.config
问题5：
Warning: Bad CRC, using default environment
问题6：
Error: can't write fw_env to flash
5和6解决办法：
将Env. size 和 Flash sector size改为arch/mips/cq8401/com/setup.c中
所设定的值。
fw_env.config文件的内容
# Configuration file for fw_(printenv/saveenv) utility.
# Up to two entries are valid, in this case the redundand
# environment sector is assumed present.
# MTD device name   Device offset   Env. size   Flash sector size
/dev/mtd2       0x0000      0x20000     0x20000
3.内核的修改
设置分区：
将arch/mips/cq8401/com/setup.c修改为以下，可以直接刷bootloader分区而不会将u-boot的配置空间擦除掉
static struct mtd_partition cq8401_mtd_parts[] = {
{
.name =     "ROOTFS",
.size =     0xC00000,
.offset =   0,
.mask_flags =   0,
},
{
.name =     "BOOTLOADER",
.size =     0x40000,
.offset =   MTDPART_OFS_APPEND,
//.mask_flags =   MTD_WRITEABLE,  /* force read-only */
.mask_flags =  0,
},
{
.name =     "uboot_env",
.size =     0x20000,
.offset =   MTDPART_OFS_APPEND,
.mask_flags =  0,
},
{
.name =     "KERNEL",
.size =     MTDPART_SIZ_FULL,
.offset =   MTDPART_OFS_APPEND,
.mask_flags =   0,
}
进入系统可用
cat /proc/mtd
查看分区设置
根据uboot的配置空间的设备节点设置/etc/fw_env.config中的第一项MTD device name,根据其偏移地址设值Device offset，根据空间大小设置Env. size ，根据闪存扇区大小设置Flash sector size
如果需要保存和恢复uboot的配置空间，用以下命令：
dd if=/dev/mtd2 of=env.bin 将配置空间的内容保存为文件env.bin
dd if=env.bin of=/dev/mtd2 将配置文件env.bin写回配置空间
如果需要读出配置空间的内容，使用以下命令：
fw_printenv
如果需要单独修改uboot的参数，使用以下命令：
fw_setenv bootdelay 5
u-boot更新脚本
#! /bin/sh
echo "##########################################"
echo "Save uboot_env  space"
dd if=/dev/mtd2 of=env.bin
echo "Erasure bootloader"
flash_eraseall /dev/mtd1
echo "Erasure uboot_env space"
flash_eraseall /dev/mtd2
echo "Ersure kernel "
flash_eraseall /dev/mtd3
echo "##########################################"
echo "Write new bootloader"
flashcp /bootloader/u-boot.bin.336new  /dev/mtd1
echo "Update u-boot completed"
echo "Write new kernel"
flashcp /bootloader/uImage /dev/mtd3
echo "Update kernel completed"
echo "Write uboot coonfig"
dd if=env.bin of=/dev/mtd2
echo "UPDATE completed"
echo "##########################################"