Multi-ported memories are challenging to implement on FPGAs since the block RAMs included in the fabric typically have only two ports. Hence we must construct memories requiring more than two ports, either out of logic elements or by combining multiple block RAMs. We present a thorough exploration and evaluation of the design space of FPGA-based soft multi-ported memories for conventional solutions, and also for the recently proposed Live Value Table (LVT) [LaForest and Steffan 2010] and XOR [LaForest et al. 2012] approaches to unidirectional port memories, reporting results for both Altera and Xilinx FPGAs. Additionally, we thoroughly evaluate and compare with a recent LVT-based approach to bidirectional port memories [Choi et al. 2012].

Multi-ported memories are challenging to implement with FPGAs since the block RAMs included in the fabric typically have only two ports. Any design that requires a memory with more than two ports must therefore be built out of logic elements or by combining multiple block RAMs. The recently-proposed Live Value Table (LVT) [8] design provides a significant operating frequency improvement over conventional approaches. In this paper we present an alternative approach based on the XOR operation that provides multi-ported memories that use far less logic but more block RAMs than LVT designs, and are often smaller and faster for memories that are more than 512 entries deep. We show that (i) both designs can exploit multipumping to trade speed for area savings, (ii) that multipumped XOR designs are significantly smaller but moderately slower than their LVT counterparts, and (iii) that both the LVT and XOR approaches are valuable and useful in different situations, depending on the constraints and resource utilization of the enclosing design.