RISC-V gained a lot of early adoption by replacing weird in-house ISAs that people were using for control-plane things. Most of these didn’t really have serious PPA requirements. They were a tiny fraction of a total chip so even doubling the area or power made a negligible impact on the total chip.
When I was at MS, I worked with a team to replace an Arm core with a RISC-V core. The core was around 1% of the total area of the subsystem, the subsystem was around 1% of the total area of the SoCs that it went in. The choices were:
- Arm
- Some bespoke in-house ISA.
- Some other licensed core.
- RISC-V
RISC-V won because we could get (or build) cores that we could integrate in the subsystem and license onwards (Arm would not allow us to sublicense one of their cores in the subsystem, their lawyers don’t like money unless they’re allowed to lick it first). Anything else came with toolchain-maintenance expenses which would easily be more than the cost of a core license.
The big win for RISC-V was that someone else paid for the toolchain and the licenses were lower than anything else where that was the case.
