DRAM selection and configuration for real-time mobile systems

The performance and power consumption of mobile DRAMs (LPDDRs) depend on the configuration of system-level parameters, such as operating frequency, interface width, request size, and memory map. In mobile systems running both real-time and non-real-time applications, the memory configuration must satisfy bandwidth requirements of real-time applications, meet the power consumption budget, and offer the best average-case execution time to the non-real-time applications. There is currently no well-defined methodology for selecting a suitable memory configuration for real-time mobile systems. The worst-case bandwidth, average-case execution time, and power consumption of mobile DRAMs across generations have furthermore not been investigated. This paper has two main contributions. 1) We analyze the worst-case bandwidth, average-case execution time, and power consumption of mobile DRAMs across three generations: LPDDR, LPDDR2 and Wide-IO-based 3D-stacked DRAM. 2) Based on our analysis, we propose a methodology for selecting memory configurations in real-time mobile systems.We show that LPDDR (32-bit IO), LPDDR2 (32-bit IO) and 3D-DRAM (128-bit IO) provide worst-case bandwidth up to 0.75 GB/s, 1.6 GB/s and 3.1 GB/s, respectively. We furthermore show for an H.263 decoder that LPDDR2 and 3D-DRAM reduce power consumption with up to 25% and 67%, respectively, compared to LPDDR, and reduce the execution time with up to 18% and 25%.