Agilex™ 7 F-Series and I-Series FPGA Memory Subsystem IP User Guide

ID 789389
Date 7/15/2024
Public
Document Table of Contents

3.1.1.4. Memory Subsystem Auto-Precharge

When you enable the auto-precharge feature, the memory-specific adaptor keeps track of opened DRAM rows per bank and issues an auto-precharge request on the last AXI transaction (within a certain window of AXI transactions) to an opened row.

This feature allows the preemptive closing of an opened DRAM row to avoid the overhead of an explicit precharge command for a subsequent AXI transaction that accesses a different row. This behavior is especially beneficial for applications that require random accesses to the memory (such as look up) because in these scenarios, the likelihood that a subsequent AXI transaction can reuse the same physical pages of a previous AXI transaction is low.

A single AXI read or write transaction can translate into one or more DDR4 BL8 memory accesses, due to write replication, width adaptation, or AXI burst. The memory-specific adaptor can automatically determine—based on the static address mapping—whether a DDR4 memory access represents the last time a physical page is accessed within the current AXI transaction, and issues the DDR4 command with auto-precharge enabled accordingly. Within an AXI transaction, pages that are accessed repeatedly can be left open during that transaction.