Accounting for clock frequency variation in the analysis of distributed factory control systems

Micro-controllers are now widely deployed as components in distributed systems. Temporal predictability is often important for such embedded systems - i.e., software must execute within specified time bounds to maintain the safe operation of the system as a whole. Micro-controller clocks exhibit random variation in resonant frequency from one component to another, a temperature sensitivity and gradual changes with time. Thus, the execution speed of software will vary when implemented on different processors of the same class. We highlight the vulnerability of standard scheduling analysis in the presence of clock frequency uncertainty when applied to the performance prediction of distributed embedded systems. We propose a modified scheduling analysis to account for the inevitable range of processor clock rates in embedded distributed systems and confirm our analysis by an empirical study using CAN for inter-processor communication.