U-boot upgrading on Pine64 checked out from public tech library

[xalius]

The SPI flash has to be attached to SPI0 and comes last in the boot priority list, so it is only booted if you do not have valid boot0 on the sdcard or eMMC. The new SOPine modules have a SPI Flash on board, but you can add one via the expansion headers to regular pine boards as well.

More Info: http://linux-sunxi.org/Bootable_SPI_flash

A64 boot sequence:

Code:

boot-> check fel key pressed (yes)--> FEL mode (boot from USB OTG)
                        \  
                    (no) \
                          \-------> 1) try to boot from SMHC0 (SD card)
                                    2) try to boot from SMHC2 (eMMC)
                                    3) try to boot from SPI0 (SPI NOR Flash)
                                    4) FEL mode (boot from USB OTG)