TF-A (ARM Trusted Firmware-A), developed by ARM, operates at the highest privilege level (EL-3) under ARMv8-A, providing APIs for switching between the secure world and non-secure world. After TF-A completes initialization, it jumps to execute U-Boot (already loaded into DRAM by x-boot).
A secure monitor which runs at EL3.
Responsible for running OP-TEE (BL32).
Responsible for running U-Boot (BL33).
Core 0 brings up OP-TEE.
Core 0 jumps to run U-Boot and then run Linux.
Linux wake up core 1, 2 and 3.
