Worst Case Analysis of DRAM Latency in Multi-requestor Systems

As multi-core systems are becoming more popular in real-time embedded systems, strict timing requirements for accessing shared resources must be met. In particular, a detailed latency analysis for Double Data Rate Dynamic RAM (DDR DRAM) is highly desirable. Several researchers have proposed predictable memory controllers to provide guaranteed memory access latency. However, the performance of such controllers sharply decreases as DDR devices become faster and the width of memory buses is increased. In this paper, we present a novel, composable worst case analysis for DDR DRAM that provides improved latency bounds compared to existing works by explicitly modeling the DRAM state. In particular, our approach scales better with increasing number of requestors and memory speed. Benchmark evaluations show up to 62% improvement in worst case task execution time compared to a competing predictable memory controller for a system with 8 requestors.