Recently, there has been an increasing drive to consolidate multiple microcontrollers into one physical entity, due to advantages in reducing overall costs, enhancing reliability, and simplifying hardware interconnections. To reduce consolidation engineering costs, minimizing system latency and memory footprint is important as well as maintaining compatibility with legacy software. In this paper, we propose a virtualization-based solution called Feather-weight Virtual Machine (FVM) that focuses on these goals.FVMenables low latency by specializing the virtualization model to Real-Time Operating Systems (RTOSes), achieves small footprint by adapting management policies to microcontroller memories, attains high compatibility by aligning with microcontroller ecosystem idiosyncrasies, finally allowing practical consolidation across a wide range of commodity microcontrollers. We implement and evaluateFVMon ARMv6-M, ARMv7-M, and RISC-V architectures with two toolchains and two RTOSes, and it can fit into 20 KiB of RAM with less than 5% latency bloat.