External Memory Interfaces Intel® Agilex™ FPGA IP User Guide

ID 683216
Date 6/20/2022
Public

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3.3. Intel® Agilex™ EMIF Calibration

The calibration process compensates for skews and delays in the external memory interface.

The calibration process enables the system to compensate for the effects of factors such as the following:

  • Timing and electrical constraints, such as setup/hold time and Vref variations.
  • Circuit board and package factors, such as skew, fly-by effects, and manufacturing variations.
  • Environmental uncertainties, such as variations in voltage and temperature.
  • The demanding effects of small margins associated with high-speed operation.

For a given external memory interface, calibration occurs on multiple pins in parallel whenever possible; however, some operations still operate on individual byte lanes sequentially. Interfaces in a row are calibrated in the order in which they are connected to the calibration IP (first the interface connected to calbus_0, then the interface connected to calbus_1, and so forth.)

Note:

The calibration process is intended to maximize margins for robust EMIF operation; it cannot compensate for an inadequate PCB layout. Examples of PCB-related issues that cannot be calibrated, include the following:

  • Excessive skew between signals within a byte lane.
  • Inter-symbol interference caused by suboptimal trace topology, such as multiple vias, impedance mismatches, or discontinuities.
  • Simultaneously-switching signal effects (victim/aggressor coupling caused by insufficient trace spacing, broadside coupling, or layer-to-layer coupling.
  • Electrical noise effects such as improper plane referencing, split-plane crossing, routing signals too close to noisy sources such as switching power supplies or other high-frequency noise generators.
  • Impedance mismatches, such as improper choices for FPGA/DRAM-side transmit/receive termination relative to PCB trace impedance, or excessive loading on the address/command or data buses due to multiple loads.

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