ICS2021

14 June 2021

Luke Leighton bio

Luke Kenneth Casson Leighton specialises in Libre Ethical Technology. He has been using, programming and reverse-engineering computing devices continuously for 44 years, has a BEng (Hons), ACGI, in Theory of Computing from Imperial College, and recently put that education to good use in the form of the Libre-SOC Project: an entirely Libre-Licensed 3D Hybrid CPU-VPU-GPU based on OpenPOWER. He writes poetry and has been developing a HEP Physics theory for the past 36 years in his spare time.

SVP64 Abstract

The OpenPOWER ISA has a strong multi-decades pedigree in Supercomputing: Matrix Multiply, 128-bit SIMD, BCD, Decimal Floating-point have been part of the ISA for decades, supporting Business and Scientific Computing. What the OpenPOWER ISA does not have is Vector processing, first successfully found in the Cray-1 Supercomputer, from 1976.

SVP64 is an initiative being developed by the Libre-SOC team and funded by NLnet, that brings Cray-style Variable-length Vectorisation to the OpenPOWER ISA in a seamless and non-disruptive fashion. The team is keeping the OpenPOWER Foundation appraised of progress, and plans to submit SVP64 as an RFC to the newly-formed OpenPOWER ISA Working Group.

SVP64 is based on the concept of embedding scalar operations into a Vectorisation Context: effectively a simple Sub-Program-Counter for-loop. However that Vectorisation Context effectively extends each of the 200+ primary scalar operations in the OpenPOWER ISA by a factor of 4,000, to produce a staggering and unprecedented 800,000 unique Vector opcodes.

Although SVP64 borrows from innovations in Computer Science over the past 50 years, including the original Cray Vectors, VLIW, Zero-overhead Loops from DSPs and Intel MMX, the end result is something entirely new. This talk will go through the development process of SVP64 and explain some of the innovative Vectorisation concepts that have never been seen before in any commercial or academic Vector ISA, including Twin-Predication and Condition Register "Post-result" predication, and how these will benefit Supercomputing performance and decrease power consumption, most notably by reducing program size and thus I-Cache usage whilst still maintaining high data throughput.

Comprehensive life-cycle of mixed testing: HDL to gates

The Libre-SOC Project is developed by Software Engineers with a Hardware background: in particular, Software Engineers with decades of experience in the Libre / Open software ecosystem. There is a huge difference.

Software Engineers have it drummed into them from either training or bitter experience that unit tests are critical at every level. Whilst the Validation Process for an ASIC goes through a rigorous process in the Synthesis Tools to ensure its correctness at every step, the actual HDL itself, shockingly, is typically put together in its entirety. Only on completion are high-level (binary) unit tests run. Errors in a low-level subsystem thus become extremely hard to find.

In addition to that, as a Libre Project, we have had to use Libre VLSI tools. These are in active development and have not - yet - been used to develop ASICs beyond 130nm or over 1,000,000 gates. Our ASIC toolchain and HDL verification procedures are therefore functional but a little different from Industry-standard (proprietary) norm.

This talk will therefore show, by example, how we went from low-level modules (with unit tests and Formal Correctness Proofs), to pipelines (with unit tests and Formal Correctness Proofs), to a functional Core (with several thousand unit tests), right the way to ASIC layout, from which the Netlist was extracted and then co-simulated with cocotb. At each and every stage - both pre and post layout and on FPGA - it has been possible to run the exact same JTAG Boundary Scan and basic startup procedure.

Jean-Paul Chaput bio

Jean-Paul Chaput holds a Master Degree in MicroElectronics and Software Engineering. He joined the LIP6 laboratory within Sorbonne Université or SU (formerly UPMC) in 2000. Currently he is a Research Engineer in the Analog and Mixed Signal Team at LIP6. His main focus is on physical level design software. He is a key contributor in developing and maintaining the Alliance/Coriolis VLSI CAD projects for CMOS technologies. In particular he contributed in developing the routers of both Alliance/Coriolis and the whole Coriolis toolchain infrastructure. He his now a key contributor in extending Alliance/Coriolis to the Analog Mixed-Signal integration for nanometric CMOS technologies.

ICS 2021 Abstract

Starting in 1990, Sorbonne Université-CNRS/LIP6 developed Alliance, a complete VLSI CAD toolchain released under GPL. In this spirit, we are assembling an upgraded design flow for ASICs based on FOSS tools like GHDL & Yosys for logical synthesis and Coriolis2 for physical design. We will present the flow with a focus on the Coriolis2 part and the LibreSOC first prototype. This should be an important milestone toward the creation of an open hardware community.