BBB u-boot

[Christian Mauderer]

Am 22.09.2017 um 08:28 schrieb Chris Johns:
> On 22/09/2017 16:13, Sichen Zhao wrote:
>> Can you please tell me which version of u-boot you used?
>> My version is old: U-Boot SPL 2014.04-00014-g47880f5 (Apr 22 2014 - 
>> 13:23:54)
> 
> I built git://git.denx.de/u-boot.git master and I think commit
> 8a1c44271c55961fb70fb6177f9c02fdb05287c5. Looking at the trace in a little more
> detail I see `U-Boot 2013.04-dirty (Jul 10 2013 - 14:02:53)` which seems wrong.
> I am now confused.
> 
> My uEnv.txt is being read from the mmc ...
> 
> ] gpio: pin 53 (gpio 53) value is 1
> ] mmc0 is current device
> ] micro SD card found
> ] mmc0 is current device
> ] gpio: pin 54 (gpio 54) value is 1
> ] SD/MMC found on device 0
> ] reading uEnv.txt
> ] 182 bytes read in 3 ms (58.6 KiB/s)
> ] Loaded environment from uEnv.txt
> 
> That is how I am controlling the boot. Could I be booting from the on-chip flash?
> 
> Chris

Hello Chris,

first of all: I don't think that the problem depends on the U-Boot
version. It sounds more like a problem due to the missing FDT. Maybe
there is a check missing whether the register that should contain the
FDT address is set correctly?

Regarding the point which U-Boot is booted: The boot process on the
Beagle Bone is a little odd. I'm still not 100% sure about it. Basically
it seems roughly about the following:

If you don't press the S2-Switch during power-up a first U-Boot ("U-Boot
SPL") is read from the boot sector of the on-board eMMC. It loads a
second U-Boot from the active partition of the eMMC. The second U-Boot
checks a number of sources to boot from. I think that depends a little
on the version of the U-Boot environment on the eMMC. My BBB (with a
U-Boot 2014.04-00014-g47880f5) tries to read the uEnv.txt from the
SD-Card and parses it if the file is available. If not it boots some
default from the internal eMMC.

If you press the S2-Switch during power-up (a reset isn't enough; it has
to be a power cycle), the controller tries to boot from the SD-Card. If
you have a "U-Boot SPL" in the boot sector there, it will use this U-Boot.

I think I've read somewhere that it is possible to mark the internal
partition as "not active" so that the U-Boot SPL of the eMMC directly
starts the U-Boot from an active partition on the SD-Card instead. But I
never tried or tested that.

Regards

Christian