I'm surprised this post even came through. The beagleboard forum
/moved/ to a new web-based-only system (which I have refused to fight with
-- I tried but found it cryptic and unusable for someone accustomed to
newsreader clients which fetch all messages in a batch and permit later
responses to be made; I abhor web-based "fetch one message, make a reply,
send, fetch next message")
The Google Groups forum has been abandoned.
On Wed, 1 Sep 2021 16:50:11 +0100, in gmane.comp.hardware.beagleboard.user
Chris Green <[email protected]> wrote:
>If one has a BBB which normally boots from eMMC is it possible to
>write a script that will reboot from the microSD card?
>
On current Beagle systems, it is u-Boot which determines the boot
device dynamically.
That is:
By default the u-Boot in the eMMC starts processing
It then scans for a bootable uSD card
If a valid uSD card is found, it toggles the boot device to be
the
uSD card, and proceeds to load the configuration from the uSD card;
otherwise it continues to load the configuration from the eMMC
If there is no u-Boot (and maybe other files) found on the eMMC, the
SoC [hardware] boot sequence is to look for a valid uSD card and load
u-Boot from that card.
The end state: if a bootable uSD card exists, it automatically becomes
the booted image, skipping the rest of the eMMC (u-Boot comes from the
first version found: eMMC then uSD).
Prior to this form of u-Boot, one was required to hold down the
boot-select button on the BBB to force uSD card load. But that form of
u-Boot vanished near the end of the Wheezy era (Debian 7). This was also
the days of kernel loaded device tree overlays -- u-Boot loaded overlays
came in during the Jessie (Debian 8) era. The two u-Boots are totally
INCOMPATIBLE with Debian versions of the other style (Wheezy u-Boot does
not load DTOs, but Jessie and later Debian kernels expect to find the DTOs
already loaded).
I don't know enough about u-Boot and uEnv.txt to know if there is some
way to modify uEnv.txt to /not/ transfer control to the uSD card except
when you want to do you back-up stuff.
--
Dennis L Bieber
--
For more options, visit http://beagleboard.org/discuss
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