Dynamically reconfigurable register file for a softcore VLIW processor

This paper presents dynamic reconfiguration of a register file of a Very Long Instruction Word (VLIW) processor implemented on an FPGA. We developed an open-source reconfigurable and parameterizable VLIW processor core based on the VLIW Example (VEX) Instruction Set Architecture (ISA), capable of supporting reconfigurable operations as well. The VEX architecture supports up to 64 multiported shared registers in a register file for a single cluster VLIW processor. This register file accounts for a considerable amount of area in terms of slices when the VLIW processor is implemented on an FPGA. Our processor design supports dynamic partial reconfiguration allowing the creation of dedicated register file sizes for different applications. Therefore, valuable area can be freed and utilized for other implementations running on the same FPGA when not the full register file size is needed. Our design requires 924 slices on a Xilinx Virtex-II Pro device for dynamically placing a chunk of 8 registers, and places registers in multiples of 8 registers to simplify the design. Consequently, when 64 registers is not needed at all times, the area utilization can be reduced during run-time.