Tow-boot problems and restoring uboot
Today I ran into issue #1 listed in the Mobian Wiki, where the boot process stops at a black screen.

Holding in the power button resulted in the phone rebooting rather than powering off, where the cycle repeated. It took several tries to get Mobian booted up. Tried the reset button in the back and finally had to remove the battery even though that's not recommended. This was a real pain, so for now I'd like to go back to uboot which never seemed to have any problems.

Before installing tow-boot I took an image backup of the eMMC using jumpdrive. Obviously the entire image could be copied back to the eMMC, but would it be possible to just extract uboot from there and write it to the eMMC using dd? What is the offset and length of the uboot image?
Did you install tow-boot to the SPI? And is is the PP or the PPP?
(04-19-2022, 10:06 AM)Fish Wrote: Did you install tow-boot to the SPI? And is is the PP or the PPP?

It's the standard Pinephone with tow-boot installed to the eMMC.
There's quite a lot of detail on the bootloader layout here:

That explains the bs=1024 seek=8 at the end of the dd command given for installing u-boot given in multiple locations. It doesn't help with the size though, so it may be better to track down u-boot-sunxi-with-spl.bin or u-boot-sunxi-with-spl-pinephone.bin either in the backup filesystem (assuming it wasn't purged before you backed up) or from the old package.
Thanks! Probably easier and less hassle to just restore my image backup, just takes longer. Smile
How does one locate the u-boot boot sector on a SD card and delete it to enable tow-boot's volume down while powering on dual boot feature?
Based on the doc linked in post #4 I think zeroing 32k starting at an 8k offset should remove enough of the u-boot from the SD for the pinephone to boot from eMMC, but I haven't tried it. Something like this, assuming I've remembered which device is uSD and which eMMC - do check!
dd if=/dev/zero of=/dev/mmcblk0 bs=1024 seek=8 count=32
Since I started this thread I should probably follow up and say I never did get around to reflashing the eMMC with a non-tow-boot image. The problems I described have not happened again so for now I'm just going to leave it as-is. I'll be sure to keep an image without tow-boot around just in case. (I do love the convenience of the built-in Jumpdrive functionality for making image backups.)

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