External Memory Interface Handbook Volume 3: Reference Material: For UniPHY-based Device Families

ID 683841
Date 3/06/2023
Document Table of Contents

8.1.1. Avalon-MM Slave Read and Write Interfaces

The read and write blocks accept read and write requests, respectively, from the Avalon-MM interface. Each block has a simple state machine that represents the state of the command and address registers, which stores the command and address when a request arrives.

The read data passes through without the controller registering it, as the PHY takes care of read latency. The write data goes through a pipeline stage to delay for a fixed number of cycles as specified by the write latency. In the full-rate burst length of four controller, the write data is also multiplexed into a burst of 2, which is then multiplexed again in the PHY to become a burst of 4 in DDR.

The user interface to the controller has separate read and write Avalon-MM interfaces because reads and writes are independent of each other in the memory device. The separate channels give efficient use of available bandwidth.