Methodology for designing statically scheduled application-specific SDRAM controllers using constrained local search

This paper presents an automatic method for generating valid SDRAM command schedules which obey the timing restrictions of DDR2 memory from a set of memory references. These generated schedules can be implemented using a static memory controller. A complete knowledge of the sequence of memory references in an application enables the scheduling algorithm to reorder memory commands effectively to reduce latency and improve throughput. While statically scheduled command schedules might be considered too inflexible to be useful in mask-defined devices, they are well suited to implementation within an FPGA where new applications can be targeted by recompilation and reconfiguration. Static SDRAM schedules generated using our approach show a median 4× reduction in the number of memory stall cycles incurred across a selection of benchmarks when compared to schedules produced dynamically by the Altera High Performance Memory Controller.