[U-Boot-Users] Accessing U-Boot ENV variables from Linux

[U-Boot-Users] Accessing U-Boot ENV variables from Linux

[Raghu]

Hello All, 

I have a serial number and a MAC address stored as the
U-Boot environment variables. A block of NAND flash
device of size 128K is assigned for persistance. 

Is there a way that I can modify or change these
variables from Linux kernel, OR what would I have to
do to get this done. 

Warm Regards,
Raghu


       
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[U-Boot-Users] Accessing U-Boot ENV variables from Linux

[Ben Warren]

Raghu,

On Wed, 2007-07-25 at 11:50 -0700, Raghu wrote:
> Hello All, 
> 
> I have a serial number and a MAC address stored as the
> U-Boot environment variables. A block of NAND flash
> device of size 128K is assigned for persistance. 
> 
> Is there a way that I can modify or change these
> variables from Linux kernel, OR what would I have to
> do to get this done. 
> 
> Warm Regards,
> Raghu

There's source code for a Linux user-space utility in /tools/env called
'fw_printenv' that will allow you to access the U-boot environment
through MTD.  I use it all the time.

regards,
Ben

[U-Boot-Users] Accessing U-Boot ENV variables from Linux

[Greg Lopp]

You would need to..
1) Have mtd (memory technology device) support in your kernel
2) Know the blocksize of your device
3) Know the offset to the environmental variables block
4) Write a program that..
4.1) open() the mtd device node
4.2) lseek() to the environmental block
4.3) read() the environmental block
4.4) Skip over the first 4 bytes (it's the checksum)
4.5) Parse through the series of \0 terminated strings until you find the
env var you are interested in
Stop here, if you only need to read vars. To write one....
4.6) Insert/update your variable's value
4.7) Use the checksum calculation table from the u-boot source to recalc the
chksum
4.8) Copy the checksum to the first four bytes of your new copy of the env
block
4.9) erase the env block on the device (ioctl(fd, MEMERASE, &erase_info)
4.A) lseek() to the env block
4.B) write() your new copy of the env block

I wrote one of these for our NOR device.  Should be the same for NAND,
right?  All the differences should be handled by the MTD layer.

On 7/25/07, Raghu <raghu_dk@yahoo.com> wrote:
>
> Hello All,
>
> I have a serial number and a MAC address stored as the
> U-Boot environment variables. A block of NAND flash
> device of size 128K is assigned for persistance.
>
> Is there a way that I can modify or change these
> variables from Linux kernel, OR what would I have to
> do to get this done.
>
> Warm Regards,
> Raghu
>
>
>
>
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[U-Boot-Users] Accessing U-Boot ENV variables from Linux

[Ben Warren]

Nethra,

On Fri, 2007-07-27 at 02:42 -0700, nethra_gmit at yahoo.co.in wrote:
> i m not getting 'fw_printenv' after compiling u-boot..
> 
> [nethra at localhost u-boot-1.1.2]$ cd tools/env
> [nethra at localhost env]$ ls
>            fw_env.c  fw_env.config  fw_env.h  fw_env_main.c  Makefile  README
> 
> can i know how to use this proprerly..?

A few things:

1. Please don't e-mail me without including the U-boot list unless it's
something only I would be interested in, such as cheap Cialis or maybe
the chance to help recover millions of dollars from the widow of Saddam
Hussein's cousin-in-law.

2. Please don't top post.

That out of the way...

This tool isn't built by default.  I've attached a couple of patches
that apply cleanly to the latest git tree:

- The first turns on building of the tool.
- The second fixes compile errors and warnings that I came across a few
months ago.  I expect you'll need it if you're using Linux 2.6.  If
you're using a 2.4 kernel, I don't know if this is needed or not.

regards,
Ben
 
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