On Fri, Jun 30, 2017 at 11:04 PM, Sergey Manucharian <s...@ara-ler.com> wrote:
> Oh, thanks, William, I was inspired doing this by your post!
>
> The problem is that "usb start" starts u-boot's USB subsystem, it (probably)
> has nothing to do with the CPU.
> You explicitly mentioned that used a USB HDD with external power supply, but
> I'm trying to boot off a USB flash drive. The CPU doesn't provide USB power
> at early stage. If I provide power from an external source, everything works
> fine.
>
> The latest u-boot supports loading overlays, I'm not sure whether it's
> possible to load an overlays with the correct configuration of that pin and
> then load kernel and stuff from USB flash drive.

Why not?

zImage:

"loadimage=load ${devtype} ${bootpart} ${loadaddr} ${bootdir}/${bootfile}\0" \

https://github.com/eewiki/u-boot-patches/blob/master/v2017.07-rc2/0001-am335x_evm-uEnv.txt-bootz-n-fixes.patch#L507

overlay:

"load ${devtype} ${bootpart} ${rdaddr} ${uboot_overlay}; " \

https://github.com/eewiki/u-boot-patches/blob/master/v2017.07-rc2/0002-U-Boot-BeagleBone-Cape-Manager.patch#L800

both use the devtype & bootpart references..  Thus if the kernel/dtb
are on the same partition of the usb flash drive as the overlays,
everything just works..

But, you'll need to add the usb options here:

https://github.com/eewiki/u-boot-patches/blob/master/v2017.07-rc2/0001-am335x_evm-uEnv.txt-bootz-n-fixes.patch#L277

Regards,

-- 
Robert Nelson
https://rcn-ee.com/

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