This whitepaper compares four approaches to storing program code on flash memory, including eXecute-in-place (XIP), fully shadowed, demand paging, and “balanced” XIP. It concludes that balanced XIP can save memory costs, while lowering launch time, especially when used with the open source AXFS (advanced XIP filing system) for Linux.

The paper was authored by three engineers at Numonyx, an Intel and STMicroelectronics joint venture aimed at commercializing the phase-change memory jointly developed by Intel and STM. The paper's authors also contribute to the AXFS filesystem project, which is championed in the paper.

The paper first describes each approach, including its attributes, features, and advantages as well as concomitant drawbacks. It then tests each approach on an XScale-based mobile phone development platform, documenting how much RAM and Flash are needed, and how quickly OSes and applications launch. It winds of up with a comparison of two Linux filesystems suitable for use with balanced XIP, including CRAMFS and AXFS. To learn more, click below for the full paper.

 
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