Virtual Memory Support for NoMMU Linux on High-Performance Microcontroller Units
High-performance microcontroller units (MCUs) such as Arm Cortex-M85 provide substantial compute capability while retaining MCU-class SWaP-C (Size, Weight, Power, and Cost) advantages. Reusing Linux software assets on such MCUs would greatly ease the development of feature-rich embedded applications with low SWaP-C requirements. NoMMU Linux, a Linux variant that does not use an MMU, supports some MCUs. However, it cannot provide the virtual memory support that some Linux applications assume, including both functional behavior, such as fork (), and efficient mechanisms, such as copy-onwrite. This research aims to provide virtual memory support for Linux applications on MCUs. The design integrates three techniques: (1) transparent memory protection unit (MPU) expansion, (2) software paging, (3) split stacks. Our proof-of-concept implementation, spanning the Linux kernel, GCC, and $\boldsymbol{\mu}$ Clibc-ng, supports fork (). We conducted a preliminary evaluation with selected LMBench programs on Arm Cortex-M85 hardware. To our knowledge, no existing Linux-kernel-based implementation has supported fork () without a hardware MMU.