How to use multiple env variables.

Hi,

Is there any option for multiple env variables so that when i upgrade the kernel and rootfile system if not working properly so that i can fall back to the previous kernel and ramdisk considering i have a sufficiently big nand with required number of partition.

thanks and regard
Shashi

Something like this works for me:
Two env variables controls from where to boot: 'ospart' indicating partition number and 'swapos' saying that there is new firmware pending. Consider NAND partitions kernel0, rootfs0, kernel1 and rootfs1. System is running from kernel1 and rootfs1 (ospart=1). Now write new system to kernel0 and rootfs0 and set variable 'swapos', then reboot system. U-Boot then executes
if test -n $swapos; then

	setenv swapos; saveenv;
	if test $ospart -eq 0; then
		setenv ospart 1;
	else
		setenv ospart 0;
	fi;

fi
and constructs kernel cmdline "root=mtd:rootfs$ospart" and then loads kernel with "nboot kernel$ospart"

Inside some OS boot script it is then discovered that system is running from diferent partition than saved in environment (we cleared 'swapos' env variable, but new 'ospart' was to saved to permanent storage) and after finding itself in sane state (based on self check or user's interaction) it sets 'ospart' in environment accordingly. Otherwise reboot is performed (based on watchdog, user's interaction...) and original OS version is loaded (as 'ospart' remains intact).

Best regards,
ladis

Hi,

Thanks for the reply at the earliest.

One doubt.

Where should this variable swapos should be.

1. should this "swapos" be in one of the separate partition of the nand flash
so that can be set by the kernel.
2. or is it a u-boot environment variable set by the kernel (reading the u-boot env
from the kernel and updating the "swapos" env) after the copy of new
kernel and ramdisk done.

Thanks and Regards
Shashi.

----- Original Message -----
From: "Ladislav Michl" <[email protected]>
To: "Shashi Kumar M.S" <[email protected]>
Cc: <[email protected]>
Sent: Thursday, January 28, 2010 3:13 PM
Subject: Re: [U-Boot] How to use multiple env variables.

Both 'ospart' and 'swapos' are ordinary u-boot environment variables.

Kernel itself doesn't keep any concept of envinronment variables, however MTD drivers live in kernel space and are used by fw_setenv (see u-boot/tools/env/README) program to alter envinroment variables stored in flash.

Sorry, I cannot parse that.

Basic idea is just to write new kernel and rootfs and execute

$ fw_setenv swapos yes
then reboot board and U-Boot scripts I described earlier do the rest.

Best regards,
ladis

Dear "Shashi Kumar M.S",

Yes, this can be trivially done. See the manual (DULG) for examples.

BTW: please make sure to use a line length of not more than 70 characters or so. Your lines are way too long!

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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