Loughborough University
vthreads_2015_R4_MicroPro-Rev1.pdf (2.83 MB)

VThreads: A novel VLIW chip multiprocessor with hardware-assisted PThreads

Download (2.83 MB)
journal contribution
posted on 2016-07-25, 13:16 authored by Vassilios Chouliaras, David Stevens, Vincent Dwyer
We discuss VThreads, a novel VLIW CMP with hardware-assisted shared-memory Thread support. VThreads supports Instruction Level Parallelism via static multiple-issue and Thread Level Parallelism via hardware-assisted POSIX Threads along with extensive customization. It allows the instantiation of tightlycoupled streaming accelerators and supports up to 7-address Multiple-Input, Multiple-Output instruction extensions. VThreads is designed in technology-independent Register-Transfer-Level VHDL and prototyped on 40 nm and 28 nm Field-Programmable gate arrays. It was evaluated against a PThreads-based multiprocessor based on the Sparc-V8 ISA. On a 65 nm ASIC implementation VThreads achieves up to x7.2 performance increase on synthetic benchmarks, x5 on a parallel Mandelbrot implementation, 66% better on a threaded JPEG implementation, 79% better on an edge-detection benchmark and ~13% improvement on DES compared to the Leon3MP CMP. In the range of 2 to 8 cores VThreads demonstrates a post-route (statistical) power reduction between 65% to 57% at an area increase of 1.2%-10% for 1-8 cores, compared to a similarly-configured Leon3MP CMP. This combination of micro-architectural features, scalability, extensibility, hardware support for low-latency PThreads, power efficiency and area make the processor an attractive proposition for low-power, deeply-embedded applications requiring minimum OS support.


This research was partially supported by the EU FP7 ENOSYS project



  • Mechanical, Electrical and Manufacturing Engineering

Published in

Microprocessors and Microsystems


CHOULIARAS, V.A., STEVENS, D. and DWYER, V.M., 2016. VThreads: A novel VLIW chip multiprocessor with hardware-assisted PThreads. Microprocessors and Microsystems, 47 pt.B, pp.466-485.


© Elsevier


  • AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Acceptance date


Publication date



This paper was accepted for publication in the journal Microprocessors and Microsystems and the definitive published version is available at http://dx.doi.org/10.1016/j.micpro.2016.07.010.






  • en