启动过程
首先根据根基mode pins来选择启动方式，SPI还是JTAG等等
然后执行片上ROM中的代码 并且从SPI 或JTAG等这些boot device中拷贝First Stage Boot Loader （FSBL）到片上内存中
最后，处理器星星FSBL，FSBL可以初始化PS的启动或者导入PL配置。FSBL可以导入用户应用或者可选的second stage boot loader
原文：
UltraScale+ RFSoCs use a multi-stage boot process that supports both a non-secure and a secure boot. The PS is the master of the boot and configuration process. For a secure boot, the AES-GCM, SHA-3/384 decryption/authentication, and 4096-bit RSA blocks decrypt and authenticate the image.
Upon reset, the device mode pins are read to determine the primary boot device to be used: NAND, Quad-SPI, SD, eMMC, or JTAG. JTAG can only be used as a non-secure boot source and is intended for debugging purposes. One of the CPUs, Cortex-A53 or Cortex-R5, executes code out of on-chip ROM and copies the first stage boot loader (FSBL) from the boot device to the on-chip memory (OCM).
After copying the FSBL to OCM, the processor executes the FSBL. Xilinx supplies example FSBLs or users can create their own. The FSBL initiates the boot of the PS and can load and configure the PL, or configuration of the PL can be deferred to a later stage. The FSBL typically loads either a user application or an optional second stage boot loader (SSBL) such as U-Boot. Users obtain example SSBL from Xilinx or a third party, or they can create their own SSBL. The SSBL continues the boot process by loading code from any of the primary boot devices or from other sources such as USB, Ethernet, etc. If the FSBL did not configure the PL, the SSBL can do so, or again, the configuration can be deferred to a later stage.
The static memory interface controller (NAND, eMMC, or Quad-SPI) is configured using default settings. To improve device configuration speed, these settings can be modified by information provided in the boot image header. The ROM boot image is not user readable or executable after boot.
来源：
Xilinx的DocNav的文档： ds809 - page32
来源：CSDN
作者：AllenGates
链接：https://blog.csdn.net/qq_17743307/article/details/104051343