Re: booting BeagleBoneGreen

["John D. Baker" <jdbaker%mylinuxisp.com@localhost>]

Getting closer.  Analyzing the eMMC contents and the microSD card to
which was written the Debian 8 image, it appears that "MLO" is written
beginning at sector 256 (0x00020000) and u-boot.img is written beginning
at sector 768 (0x00060000) of the disk.  An offset of 2048 (1MiB) for
the first MBR partition gives them plenty of space.

Preparing a microSD card in this fashion does prompt the BBG to try to
boot from it when the USER/BOOT switch is held down on power-up.  It's
important that the space between the end of the disklabel and the first
MBR partition be zeroed out and use "conv=osync" when writing the images
with 'dd'.  Otherwise, you'll see something like:


U-Boot SPL 2015.10-00001-g143c9ee (Nov 06 2015 - 15:27:19)
bad magic


U-Boot 2015.10-00001-g143c9ee (Nov 06 2015 - 15:27:19 -0600), Build: jenkins-github_Bootloader-Builder-274
                          
       Watchdog enabled
I2C:   ready           
DRAM:  512 MiB
Reset Source: Global external warm reset has occurred.
Reset Source: watchdog reset has occurred.            
Reset Source: Power-on reset has occurred.
MMC:                                      
[hangs here until watchdog times out, resetting the board, ad nauseum]


Unfortunately, it doesn't seem to read the custom uEnv.txt file (copied
from "armv7.img.gz"), so the default boot will actually boot linux from
the eMMC.  The U-Boot environment seems compiled in with no means of
saving changes.

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