On Thu, Apr 23, 2015 at 05:10:21PM +1000, Craig McQueen wrote:
I'm building Yocto for BeagleBone using the meta-ti layer and the kernel and
U-Boot provided by that layer.
I'm having some trouble understanding the location where U-Boot saves its
environment for BeagleBone Black.
After doing some reading, it looks as though it might be saving environment
on a special eMMC boot partition (which is not the same as the FAT16
partition 1 I created to store MLO and u-boot.img).
However, this is only when booting from the on-board eMMC I think. When
booting from SD card, where is environment stored? I can do saveenv command
in U-Boot, and it says it's saving it to MMC.
U-Boot# saveenv
Saving Environment to MMC...
Writing to MMC(1)... done
But then after a reboot, it says:
MMC: block number 0x100 exceeds max(0x0)
MMC: block number 0x200 exceeds max(0x0)
*** Error - No Valid Environment Area found
Using default environment
So does that mean that U-Boot can't use a saved environment when booting from
SD card?
Actually, based on some simple testing, it seems that it _is_ writing to the
boot partition of the on-board eMMC, and loading it when it reboots from SD
card, despite the error message. This is confusing.
First, please post the whole boot log, not just part. That will make it
easier to explain what is going on I believe.
What about the case of a board with no eMMC, such as BeagleBone White? Where
would it save environment then?
There's a number of different places that env could be stored. I forget
if meta-ti is patching things such that it saves to a file on the FAT
partition for example.
How can I erase the saved environment when booting from eMMC, to ensure that
U-Boot defaults will be used? I see that when Linux boots, there are block
devices /dev/mmcblk0boot0 and /dev/mmcblk0boot1. But it seems I can't write
to them:
# dd if=/dev/zero of=/dev/mmcblk0boot1 bs=1k count=1k
dd: writing '/dev/mmcblk0boot1': Operation not permitted
1+0 records in
0+0 records out
In Linux you need to unlock these first. Google should point out the
file you need to write to.
--
Tom
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