Hierarchical memory mapping during synthesis in FPGA-based reconfigurable computers

One step in the synthesis for FPGA-based Reconfigurable Computers (RCs) involves mapping the design data structures onto the physical memory banks available in the hardware. The advent of Xilinx Virtex-style FPGAs and of hierarchical memory schemes on reconfigurable boards introduced an added complexity to this mapping. The new RC boards offer a wealth of memory banks many of them on-chip (such as the BlockRAMs available in the Virtex architecture) and many of them offering variable number of ports and several depth/width configurations. Along with the external RAMs, a hierarchy of memories with varying access performances are available in a reconfigurable computer. It becomes critical to perform a good mapping to achieve optimal design performance. This paper presents an automatic memory mapping methodology which takes into account: the number of words and word size of design data segments and physical memory banks, number of ports on the banks, access latency of the banks, proximity of the banks to the processing unit, life cycle analysis of data segments, and it also incorporates configuration selection from the multiple configurations available in BlockRAMs of Virtex series FPGAs. In the case of multiple processing elements on board, the paper also provides a framework in which the task of memory mapping interacts with spatial partitioning to provide the best implementation.