Hard Processor System Technical Reference Manual: Agilex™ 5 SoCs

ID 814346
Date 4/01/2024
Public

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7.9. Clock Manager Design Guidelines and Examples

  • The main clock source is either the external HPS_OSC_CLK, the F2H_free_clk from the fabric, or an internal oscillator clock.
  • HPS clock planning involves choosing clock sources and defining frequencies of operation for the following HPS components:
    • HPS PLLs
    • MPU subsystem
    • L3 interconnect
    • HPS peripherals
    • HPS-to-FPGA user clocks
  • HPS clock planning depends on board-level clock planning, clock planning for the FPGA portion of the device, and HPS peripheral external interface planning. Therefore, it is important to validate your HPS clock configuration before finalizing your board design.
  • The HPS dedicated I/Os are LVCMOS/LVTTL supporting a 1.8V voltage level. Make sure any HPS peripheral interfaces (for example: Ethernet PHY, UART console) configured to use the HPS dedicated I/O bank as well as board-level clock circuitry for the HPS are compatible with 1.8V LVCMOS signaling.
  • The HPS_OSC_CLK can be located anywhere within the HPS dedicated I/O Bank. Use the Quartus HPS Platform Designer component to select the pin for HPS_OSC_CLK clock and verify its compatibility with other HPS peripheral I/O locations assigned to this bank.
  • Once you have validated the HPS clock configuration, 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.
  • Avoid cascading PLLs between the HPS and the FPGA. Cascading PLLs between the FPGA and HPS have 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.