Octavo: An FPGA-Centric Processor Family

Overlay processor architectures allow FPGAs to be programmed by non-experts using software, but prior designs have mainly been based on the architecture of their ASIC predecessors. In this paper we develop a new processor architecture that from the beginning accounts for and exploits the predefined widths, depths, maximum operating frequencies, and other discretizations and limits of the underlying FPGA components. The result is Octavo, a ten-pipeline-stage eight-threaded processor that operates at the block RAM maximum of 550MHz on a Stratix IV FPGA. Octavo is highly parameterized, allowing us to explore trade-offs in datapath and memory width, memory depth, and number of supported thread contexts.