Hard Processor System Booting User Guide: Agilex™ 5 SoCs

ID 813762
Date 12/20/2024
Public
Document Table of Contents

6.4.2.3. PLL Differences

Constrain all non-HPS EMIF PLLs in the design. Unconstrained PLLs might be placed in the HPS IO bank in one design but not in the other, leading to an IO hash difference.

To ensure the PLL is constrained to a specific location, it is usually enough to constrain the reference clock pin feeding the PLL. However, if the reference clock feeding the PLL comes from another PLL through cascading or is a global reference clock, the PLL might be placed in a different bank from its reference clock pin location. In this case, you should constrain the PLL cell's location directly. You can add this constraint using the Interface Planner or by setting location assignments in the QSF file.

Additionally, be aware of how the reference clock and output clocks are routed through the HPS IO bank. Ensure that any clock connected to the PLL has the same global setting across both designs. The GLOBAL_SIGNAL setting in the QSF file determines whether a clock is global.

# PLL location assignment in QSF
set_location_assignment IOPLL_X<X>_Y<Y>_N<N> -to <PLL cell path> 
# Clock global assignment in QSF
set_instance_assignment -name GLOBAL_SIGNAL ON/OFF -to <signal name>