Scalable Memory Architecture for Soft-core Processors

Restrictions over memory performance have always had a great impact on soft-core processors. The reduced number of ports on FPGAs' block RAMs may limit the exploitation of parallelism on soft-core processors that are implemented on top of these devices. Multiple memory ports on FPGAs are cumbersome and do not scale well, having a high cost in area and power consumption when implemented. In order to mitigate the impact of the memory bottleneck on such devices, we propose a scalable memory architecture for soft-cores. We make use of software-managed memories to build a memory system capable of improving performance and instruction-level parallelism (ILP) on soft-core processors. Results show that our architecture overcomes the limited parallelism realized on a dual-ported processor, reducing execution time by 16.5%. These improvements come with no area costs, as the processor is kept with the same total memory. Automated code transformations implemented within the LLVM compiler keep changes in application code to a minimum. We also show that our architecture scales better when boosting the number of functional units in the system.