One of my favorite features of the Baochip-1x is the BIO. It's an I/O coprocessor that is based on the PicoRV32, with custom register extensions to allow direct access to GPIOs from the ISA.
Read more about the BIO at this blog post: https://www.bunniestudios.com/blog/2026/bio-the-bao-i-o-coprocessor/ I go in-depth into the architecture and its trade-offs relative to the PIO, and conclude by working through a couple of coding examples.