External Memory Interfaces (EMIF) IP User Guide: Agilex™ 5 FPGAs and SoCs

ID 817467
Date 3/31/2025
Public
Document Table of Contents

3.2.9. User Clock in Different Core Access Modes

The EMIF IP for Agilex™ 5 devices supports two user access modes.
  • Synchronous fabric clocking, where the EMIF IP provides a user clock.
    • The user clock frequency is limited by the maximum core-to-periphery (C2P) and periphery-to-core (P2C) frequency of 300 MHz.
    • In DDR4, the user clock frequency will be one-quarter of the memory clock frequency ((mem_CK)/4).
    • In DDR5, LPDDR5, and LPDDR4, the user clock frequency will be one-eighth of the memory clock frequency ((mem CK)/8).
  • Asynchronous fabric clocking, where you provide the clock to the EMIF IP.
    • The asynchronous user clock can come from any user clock source on the device.
    • It is recommended to set the user clock frequency to one-quarter of the memory clock.

The following figures illustrate the different clocking styles available for the Agilex™ 5 EMIF IP.

Figure 11. Access Modes

Benefits of Each Access Mode

  • Synchronous fabric clocking is required for DDR4 DIMM.
  • Asynchronous fabric access mode has the lowest latency.
  • Asynchronous fabric access mode can achieve higher memory clock frequency in some speed grade / protocol combinations.
  • Asynchronous fabric access mode can achieve higher efficiency on secondary memory controller in the following configurations:
    • 2ch x16 LPDDR4 / LPDDR5 / DDR5
    • 4ch x16 LPDDR4 / LPDDR5
    • 1ch x16 of LPDDR4 / LPDDR5 / DDR5 on the top sub-bank

    Altera recommends using asynchronous clocking mode when you use the configuration listed above. Refer to guidelines in Optimizing Efficiency for Secondary Controller when using asynchronous clocking mode, for achieving optimal efficiency with a secondary controller.