Libre-SOC 180nm Power ISA ASIC Submitted to Imec for Fabrication
Published on Thursday 8 July 2021
The team that collaborated on the project has a wealth of expertise in software engineering and ethical hardware design, and as a matter of principle used a fully free and open source toolchain to deliver this groundbreaking chip. This makes it the first ASIC of its kind, with many more to come - each edging closer to an attractive open hardware alternative to current proprietary offerings. The project was funded by NLnet Foundation as part of its Next Generation Internet initiative, as a fundamental technological building block that will help increase privacy and trustworthiness for end users.
Implementing a fixed-point subset of the v3.0B OpenPOWER ISA, Libre-SOC’s 180nm Power ISA Test ASIC is the world’s first Power ISA implementation designed outside of IBM to go to silicon, following IBM’s open sourcing of the POWER ISA in 2019. Libre-SOC used Microwatt, which was designed by IBM and sent to Skywater for fabrication earlier this year, as a reference design for benchmarking and cross-verification.
[caption id=“attachment_7838” align=“aligncenter” width=“500”] Snapshot of the 180nm GDS-II file laid out automatically with coriolis2[/caption]
The ASIC is 130,000 gates, measures 5.5 x 5.9 mm^2, contains four 4k SRAMs developed by Chips4Makers, and a 300 mhz Voltage-Controlled PLL developed by Professor Galayko of Sorbonne Université. The VLSI tape-out was carried out by Jean-Paul Chaput of Sorbonne Université using coriolis2, and the Static Timing Analysis and LVS checking by Dr. Marie-Minerve Louërat of Sorbonne Université. The HDL of the core is entirely in nmigen, a python Object-Orientated HDL.
The Cell Library used, FlexLib, also sponsored by NLnet, was developed by Staf Verhaegen of Chips4Makers, and is Libre-Licensed. Symbolic (ghost) versions of FlexLib allowed Libre-SOC developers to not have to sign a Foundry NDA during the development of the ASIC Layout: an important requirement to fulfil their transparency obligations to NLnet under the Privacy and Enhanced Trust Programme.
LIP6 developed the VLSI ASIC Layout tool, coriolis2. Coriolis2 is also entirely Libre-licensed and is a fully automated HDL to GDS-II tool which requires no manual intervention. It is independent of OpenLANE, is developed entirely in Europe, and has the same fully automated capability of turning HDL into 100% DRC clean GDS-II.
LIP6 were able to create the GDS-II tape-out under NDA using “Real” (non-symbolic) versions of Chips4Makers’ FlexLib, whilst Libre-SOC developers assisted using Symbolic Cells.
“We developed this ASIC on the Power architecture because of its supercomputing pedigree, and the decades-long commitment and stability that IBM and other OpenPOWER Foundation members have sustained,” said Luke Kenneth Casson Leighton, lead developer and project coordinator for Libre-SOC. “On this strong base, we can build a reliable, efficient Hybrid 3D CPU-VPU-GPU, and our next test ASIC will include Draft Cray-style Vector Extensions, SVP64.”
For more information, contact the developers of Libre-SOC at http://libre-soc.org.