A Software Reproduction of Virtual Memory for Deeply Embedded Systems

摘要

Both the hardware cost and power consumption of computer systems heavily depend on the size of main memory, namely DRAM. This becomes important especially in tiny embedded systems (e.g., micro sensors) since they are produced in a large-scale and have to operate as long as possible, e.g., ten years. Although several methods have been developed to reduce the program code and data size, most of them need extra hardware devices, making them unsuitable for the tiny systems. For example, virtual memory system needs both MMU and TLB devices to execute large-size program on a small memory. This paper presents a software reproduction of the virtual memory system especially focusing on paging mechanism. In order to logically expand the physical memory space, the proposed method compacts, compresses, and swaps in/out heap memory blocks, which typically form over half of the whole memory size. A prototype implementation verifies that the proposed method can expand memory capacity by over twice. As a result, large size programs run in parallel with a reasonable overhead, comparable to that of hardware-based VM systems.