External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Document Table of Contents NIOS II-based Sequencer Function

The sequencer enables high-frequency memory interface operation by calibrating the interface to compensate for variations in setup and hold requirements caused by transmission delays.

UniPHY converts the double-data rate interface of high-speed memory devices to a full-rate or half-rate interface for use within an FPGA. To compensate for slight variations in data transmission to and from the memory device, double-data rate is usually center-aligned with its strobe signal; nonetheless, at high speeds, slight variations in delay can result in setup or hold time violations. The sequencer implements a calibration algorithm to determine the combination of delay and phase settings necessary to maintain center-alignment of data and clock signals, even in the presence of significant delay variations. Programmable delay chains in the FPGA I/Os then implement the calculated delays to ensure that data remains centered. Calibration also applies settings to the FIFO buffers within the PHY to minimize latency and ensures that the read valid signal is generated at the appropriate time.

When calibration is completed, the sequencer returns control to the memory controller.

For more information about calibration, refer to UniPHY Calibration Stages, in this chapter.

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