As a subscriber to the “Dabao” campaign, you’re already aware of the Baochip-1x. This update fills in the backstory of what it is, why I’m doing it now, and how it came about.
The root cause turns out explicitly to be because MMUs are so valuable: without one, you can’t run Linux, BSD, or Mach. Thus, when ARM split their IP portfolio into the A, R, and M-series cores, the low-cost M-series cores were forbidden from having an MMU to prevent price erosion of their high-end A-series cores. Instead, a proprietary hack known as the “MPU” was introduced that gives some memory security, but without an easy path to benefits such as swap memory.
Meat of the story:
The RISC-V Baochip has one.