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ρ-VEX: A Reconfigurable and Extensible VLIW Processor

ρ-VEX is an open source VLIW processor with an accompanied development framework. The project started as the MSc project of Thijs van As while he was at the Computer Engineering Laboratory at Delft University of Technology.

Today, multiple research groups are still actively working on extending and improving the ρ-VEX framework.

This project was originally hosted on Google Code (at

About ρ-VEX

ρ-VEX is an open source reconfigurable and extensible Very-Long Instruction Word (VLIW) processor, accompanied by a development framework consisting of a VEX assembler, ρ-ASM. The processor architecture is based on the VEX ISA, as introduced by J.A. Fisher et al.. The VEX ISA offers a scalable technology platform for embedded VLIW processors, that allows variation in many aspects, including instruction issue-width, organization of functional units, and instruction set. The ρ-VEX source code is described in VHDL. ρ-ASM is written in C.

A software development compiler toolchain for VEX is made publicly available by Hewlett-Packard. The reasons VEX was chosen as the ISA are merely its extensibility and the quality of the available compiler. The design provides mechanisms that allow parametric extensibility of ρ-VEX. Both reconfigurable operations, as well as the versatility of VEX machine models are supported by ρ-VEX. The processor and framework are targeted at VLIW prototyping research and embedded processor design.

The name ρ-VEX stands for 'reconfigurable VEX' processor. Because the letter Rho (P or ρ) is the Greek analogous for the Roman R or r, ρ-VEX is pronounced as r-VEX. This is also the correct spelling when no Greek letters can be used.

Getting Started

To start experimenting with ρ-VEX, read the Quickstart Guide and download a release snapshot, or clone master. When you have a Xilinx University Program Virtex-II Pro Board by Digilent, you should have ρ-VEX running within moments.



A reconfigurable and extensible VLIW processor implemented in VHDL






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