External Memory Interface Handbook Volume 3: Reference Material

ID 683841
Date 7/24/2019
Public
Document Table of Contents

14. Latency for UniPHY IP

Intel defines read and write latencies in terms of memory device clock cycles, which are always full-rate. There are two types of latencies that exists while designing with memory controllers—read and write latencies, which have the following definitions:

  • Read latency—the amount of time it takes for the read data to appear at the local interface after initiating the read request.
  • Write latency—the amount of time it takes for the write data to appear at the memory interface after initiating the write request.

Latency of the memory interface depends on its configuration and traffic patterns, therefore you should simulate your system to determine precise latency values. The numbers presented in this chapter are typical values meant only as guidelines.

Latency found in simulation may differ from latency found on the board, because functional simulation does not consider board trace delays and differences in process, voltage, and temperature. For a given design on a given board, the latency found may differ by one clock cycle (for full-rate designs), or two clock cycles (for quarter-rate or half-rate designs) upon resetting the board. The same design can yield different latencies on different boards.

Note: For a half‑rate controller, the local side frequency is half of the memory interface frequency. For a full‑rate controller, the local side frequency is equal to the memory interface frequency.

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