...
Boot Loader stage (BL1): Executed by AP Boot ROM.
Execution stage 2 (BL2): Trusted Boot Firmware.
Execution stage 3-1 (BL31): EL3 Runtime Firmware.
Execution stage 3-2 (BL32): Secure-EL1 Payload.
Execution stage 3-3 (BL33): Non-trusted Firmware.
Boot process of SP7350 platform
In the SP7350 software architecture, BL1 is represented by i-boot, BL2 by x-boot, BL31 by TF-A, BL32 by OP-TEE, and BL33 by U-Boot. As shown in the figure below, the blue arrows indicate the boot sequence. Notably, i-boot, x-boot, and TF-A operate at EL3, U-Boot at EL2, while OP-TEE and Linux run at EL1.
...