CCM: Low cost dynamic data exchange to emulate RAM on NAND flash

In embedded systems, it brings great benefits to use NAND flash for dynamic data exchange like using RAM, since RAM is usually expensive and consumes much energy. However, the major hardware limitations of NAND flash make it difficult to directly and dynamically read\write\erase on NAND flash. Traditional virtual memory systems are all based on flash translation layer and file system, which lead to frequently flash read\write\erase and more RAM requirement. To address this problem, we propose a Comet Circle Model (CCM) to emulate RAM for low cost embedded systems in this paper. CCM dynamically makes the distribution of valid pages in NAND flash follow a fixed function through integrating its physical page-level mapping and circularly write-back techniques. As a result, CCM can select a block without valid pages to write data almost every time in data writing, which avoids data moving among blocks. Both theoretical analysis and experimental results show that the data moving times and erase counts of CCM closely reach the theoretical lower bounds.