The need to reprogramme a wireless sensor network may arise from

changing application requirements, bug fixes, or during the application

development cycle. Once deployed, it will be impractical at

best to reach each individual node. Thus, a scheme is required to

wirelessly reprogramme the nodes. We present an energy-efficient

code distribution scheme to wirelessly update the code running in

a sensor network. Energy is saved by distributing only the changes

to the currently running code. The new code image is built using

an edit scr ipt of commands that are easy to process by the nodes.

A small change to the programme code can cause many changes to

the binary code because the addresses of functions and data change.

A naive approach to building the edit scr ipt string would result in

a large scr ipt. We describe a number of optimisations and present

experimental results showing that these significantly reduce the edit