I want to set uboot to in following sequence
USB
sdcard
emmc
Please anyone help me to set in boot env, uEText or source code am335x_evm.h
On Wed, 14 Aug 2019 01:42:11 -0700 (PDT),
mauryan.inc@gmail.com declaimed the
following:
I want to set uboot to in following sequence
USB
sdcard
emmc
Please anyone help me to set in boot env, uEText or source code am335x_evm.h
Please study the BBB System Reference Manual (page 67 through 69). The
initial boot device is determined BEFORE uBoot gains control. UBoot is
actually the third stage boot loader -- the processor ROM code first looks
for a boot device and loads code (MLO) to set up the rest of the hardware,
and that code then loads uBoot.
I believe the uBoot on recently (last two-three years) flashed eMMC is
smart enough to transfer control to the SD card OS image if present so one
does not have to use the boot button to force SD card images to run. (I
haven't had to use the boot button since the last standard Wheezy release
was flashed to eMMC)
Overrides require using the pins shared with LCD/HDMI, which makes them
tricky to manipulate without losing the display capability -- and may still
not provide the order you want. To get USB boot requires a missing eMMC
(don't know if it just needs to be empty/erased, or physically removed), no
SD card, and the boot button pressed (or equivalent pin tied to ground),
otherwise it will attempt UART0. The two options are
eMMC, SD, UART0, USB0
SD, eMMC, USB0, UART0
You might be able to modify a version of MLO and uBoot and flash them
to eMMC so when that uBoot loads (normal boot sequence) IT will attempt to
load the OS kernel from USB0 in preference to eMMC or SD card -- I don't
believe that is something available in uEnv edits (caveat: I've not studied
it to know what is available).