3.3. Intel® Agilex™ EMIF Calibration
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.)
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.