Song-ho Yoon

Virtual-ROM: a new demand paging component for RTOS and NAND flash memory based mobile devices

Similiar to a hard disk, NAND flash memory must be accessed in sector unit, and cannot be used for code storage without copying its contents to RAM. A virtual memory technique is promising as a RAM saving solution. However, it can not be easily used without the operating system supports, and it is not suitable for real time systems because it causes unpredicted execution delays. Virtual-ROM is a light-weight demand paging solution designed for RTOS based mobile devices. It is OS-independent, easy-to-use, and well optimized for NAND flash memory. Because it occupies only a restricted address space, real time tasks can be free from unpredictable execution delays by being excluded from Virtual-ROM. Our trace driven simulation showed that its performance is similar to 70ns NOR flash memory, and our real taget adaptation for a CDMA mobile phone showed that it saved about 30% RAM usage.