Embedded Design Handbook

ID 683689
Date 8/28/2023
Public
Document Table of Contents

3.5.5.2. Disadvantages

Along with the high capacity and low cost of SDRAM, come additional complexity and latency. The complexity of the SDRAM interface requires that you always use an SDRAM controller to manage SDRAM refresh cycles, address multiplexing, and interface timing. Such a controller consumes FPGA logic elements that would normally be available for other logic.

SDRAM suffers from a significant amount of access latency. Most SDRAM controllers take measures to minimize the amount of latency, but SDRAM latency is always greater than that of regular external SRAM or FPGA on-chip memory. However, while first-access latency is high, SDRAM throughput can actually be quite high after the initial access latency is overcome, because consecutive accesses can be pipelined. Some types of SDRAM can achieve higher clock frequencies than SRAM, further improving throughput. The SDRAM interface specification also employs a burst feature to help improve overall throughput.