Ah - that led me to these. Thanks!

J2 open processor: an open source processor using the SuperH ISA - https://news.ycombinator.com/item?id=26866065 - April 2021 (45 comments)

Why the J-core open processor is cool - https://news.ycombinator.com/item?id=24163584 - Aug 2020 (1 comment)

J-Core Open Processor - https://news.ycombinator.com/item?id=20658584 - Aug 2019 (31 comments)

J-core Open Processor - https://news.ycombinator.com/item?id=12105913 - July 2016 (27 comments)

Building a CPU from Scratch: Jcore Design Walkthrough [video] - https://news.ycombinator.com/item?id=12101908 - July 2016 (8 comments)