[…]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.
https://www.fredericb.info/2018/03/emulating-exynos-4210-bootrom-in-qemu.html#emulating-exynos-4210-bootrom-in-qemu
https://github.com/frederic/qemu-exynos-bootrom
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
https://www.fredericb.info/2016/10/amlogic-s905-soc-bypassing-not-so.html#amlogic-s905-soc-bypassing-not-so
Firmware Security 