AN 886: Intel® Agilex™ Device Design Guidelines

ID 683634
Date 8/26/2022

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Document Table of Contents Internal Clocks

Once you have validated the HPS clock configuration as described in the HPS Clock Configuration Planning guidelines, you must implement your HPS clock settings under software control, which is typically done by the boot loader software. You must also follow guidelines for transferring reference clocks between the HPS and FPGA.

GUIDELINE: Avoid cascading PLLs between the HPS and FPGA.

Cascading PLLs between the FPGA and HPS has not been characterized. Unless you perform a jitter analysis, do not chain the FPGA and HPS PLLs together. Output clocks from HPS are not intended to be fed into PLLs in the FPGA.

There are specific requirements for managing HPS PLLs and clocks under software control.

For more information, refer to the "Clock Manager" section in the Intel® Agilex™ Hard Processor System Technical Reference Manual.