Why does BBB boot from MicroSD card without pressing the boot button

According to the BBB manual, the BBB should boot from MicroSD card
only if I press the boot button, yet it happens without pressing it.

This is the trace _without_ the MicroSD card that shows the BBB
booting from flash:

This is the trace _with the MicroSD card that shows the BBB booting
from the MicroSD even though I did not press the button:

When logged in _without_ the MicroSD card:
root@beaglebone:~# cat /media/BEAGLEBONE/uEnv.txt
optargs=quiet drm.debug=7

This is a BBB v. B

Any ideas?

Magic… Your welcome!

More specifically, U-Boot is configured to check if there's a uSD card
present and boots from it if found. This is intended as a convenience
and the details are specific to the version of U-Boot you have
installed. If you want to change this behavior, you can modify the
U-Boot startup script or (in some cases) remove the boot files from your
uSD card.

Thanks Charles, I understand now. Section 6.7.2 of the BBB manual
(Default Boot Options) talks from a strict hardware point of view
without mention of the behaviour of u-boot that ships with BBB that
overides the hardware behaviour (sort of).

The manual is correct. It still boots from eMMC if the button i snot pushed as the first choice.
If you push the button, it boots from SD if it is there.

What SW chooses to do do does not alter these facts. SW has no control over the boot order.


Hi Gerald,

I agree with what you said and that the manual is correct from a
hardware point of view. However it would not be out of place (in my
opinion) to add a short sentence after this paragraph in section 6.7.2
of the manual:

"If you have a uSD card from which you need to boot from, hold the
boot button down. On boot, the processor will look for the SPIO0 port
first, then uSD on the MMC0 port, followed by USB0 and UART0. In the
event there is no uSD card and the eMMC is empty, USB0 or UART0 could
be used as the board source."

The sentence I suggest could be added would be something like:
"Note however that BBB ships with U-Boot on the eMMC configured to
boot from the uSD if one is inserted even if the boot button is not