PMU firmware can be loaded by either FSBL or CSU BootROM (CBR). Both these flows are supported by Xilinx. Loading PMU firmware using FSBL has the following benefits:
- Possible quick boot time, when PMU firmware is loaded after bitstream.
- In use cases where you want two BIN files - stable and upgradable, PMU firmware can be part of the upgradable (by FSBL) image.
Important: CBR loads FSBL. If CBR also loads PMU firmware, it means that the secure headers for both FSBL and PMU firmware are decrypted with same Key-IV pair, which is a security vulnerability (security rule is: no two partitions should use the same Key-IV pair). This is addressed in FSBL, not in CBR. Hence, you should avoid CBR loading PMU firmware in secure (decryption) cases.
For DDR self-refresh over Warm restart, FSBL and PMU firmware must be loaded first (in any order) before all other images (e.g. bitstream).
For Power Off Suspend, PMU firmware must be loaded first (i.e. by CSU) before FSBL.