Re: u-boot fw_env for SD card based boot

[Simon H <btsimonh@googlemail.com>]

Thank you Vagrant, you are of course correct.
I was searching the installed image for fdtfile=, and did not find it
except inside the uboot binary (the default), but if i search for it
after having used setenv in uboot, then I find the env section at
0x88000, before the FAT at 0x100000.  (I'm on uSD card).
However, if I use

/dev/mmcblk0            0x88000         0x20000

in fw_env.config, fw_printenv complains
'Environment does not start on (erase) block boundary'

For me, the important variable is 'fdtfile', as I'm not currently
using the correct dtb for my device (because either it does not work,
or my device does not work! :), and so adjusting the boot parameters
could be important if I try to investigate the dtb.

It's not so important, as I have serial access; just would be nice to
get that familiar interface back...
Is there any documentation on distro_bootcmd?  I'm assuming from a
quick look, that uboot's default env loads boot.scr; and that this
file is a 'script image' built using mkimage?  Are there any utilities
which allow for easy manipulation of the script?

(device is aging MK802-1G; I'm using pcduino dtb.  all is good except
wifi....  Have to say to have mainline support on these devices is
fantastic - I'd run out of options for images which worked, only to
find the default Debian install was spot on).

thanks,

Simon


On Tue, Dec 20, 2016 at 1:33 PM, Vagrant Cascadian <vagrant@debian.org> wrote:
> On 2016-12-20, Simon H <btsimonh@googlemail.com> wrote:
>> Got Debian working nicely on an allwinner device with SD boot.
>>
>> The uboot variables seem to be stored in a file boot.scr in mmcblk0p1
>> (or are they in /boot/boot.scr?)
>
> The u-boot environment is not typically stored in a file on
> allwinner/sunxi platforms, rather it is usually stored on the raw deviec
> of the boot media (SD/eMMC/NAND) directly at an offset.
>
> The boot.scr is generated by flash-kernel, and you can use
> /etc/default/flash-kernel to set some values such as the boot arguments
> passed to the kernel.
>
> Since allwinner platforms with mainline u-boot support distro_bootcmd,
> you shouldn't typically need to change the default environment, the
> flash-kernel boot scripts should work out of the box.
>
>
> live well,
>   vagrant