A redesign and rewrite of the kernel software for a remote telemetry units in order to make it more responsive and less resource hungry.
A large amount of the application were moved to interrupts rather than a polling based operation. Duplicate code was removed and what was reused was made more efficient. This greatly reduced the over-all control footprint.
This system went from a heavily loaded system with no possibility of including the extra functionality to a system that was only about 50% loaded with the extra functionality.