[…]This project allows to debug BootROM dynamically with GDB. It has been helpful for analyzing secure boot mechanism that loads and authenticates the next stage from flash memory.[…]
Nicely-written. Includes coverage of U-Boot and U-Boot Secure Boot.
PS: I just learned about this blog. Catching up, there are some interesting older posts, eg:
Amlogic S905 SoC: bypassing the (not so) Secure Boot to dump the BootROM