使用TFA启动需要知道哪些概念?
1. Boot stage
BL1,BL2,BL31,BL32,BL33
2. Exception level
EL3, EL1S, EL2
3. 那么放在表格里比较一下咯
| Boot stage | Exception level | Description |
| BL1 | EL3 | Boot ROM firmware (这一段程序由硬件完成，无法修改)
Note: BL1 is embedded in hardware (Boot ROM + PBL commands)
|
| BL2 | EL3 |
Platform initialization firmware(平台初始化固件)
|
| BL31 | EL3 | Resident runtime firmware |
| BL32 | EL1S | [Optional] Trusted operating system. For example, OP-TEE |
| BL33 | EL2 | Normal world bootloader. For example, U-Boot, UEFI |
