Beginning with 14.3, users are able to make modifications to the Zynq FSBL created in the Xilinx Software Development Kit (SDK).
Xilinx provides functions that serve as user hooks. The user can addadditional functionality required into these routines. This helps retain the normal FSBL flow, while also allowing users to add their own custom logic.
The FSBL user hooks allow custom logic to be added in three different locations in the FSBL.
These three functions are left blank and have an area for user logic to be added. The functions are located in fsbl_hooks.c, which is part of the source code for a SDK generated FSBL.