What It Is, Why I'm Doing It Now, and How It Came About

Bunnie Huang details the backstory of the Baochip-1x, a RISC-V microcontroller SoC that uniquely includes a Memory Management Unit (MMU) — a feature absent from typical embedded microcontrollers due to historical ARM licensing decisions. The post explains why the MMU matters for secure, loadable apps and virtual memory, traces the convention of MMU-less embedded chips back to the ARM7TDMI era, and argues that ARM deliberately withheld MMUs from its M-series cores to protect A-series pricing. The chip was made possible by hitchhiking a VexRiscv CPU core onto a 22nm chip designed by Crossbar, Inc., which uses RRAM for non-volatile storage. The Baochip-1x runs Xous, a pure-Rust OS designed for small memory footprint devices. The post also argues for partially-open RTL SoCs as a pragmatic bridge toward a fully open silicon-to-software future, rather than waiting for fully open-source PDKs.