I. Introduction
Nowadays, many industrial control systems are real-time programs mainly implemented on Programmable Logic Controllers (PLCs). In real-time control systems, performance-related requirements such as timing requirements for response time is a highly important aspect required to be analyzed, tested and guaranteed more rigorously than other types of software systems. One of the basic language elements of the PLC-based industrial control programs are function blocks. According to the programming languages standards of programmable controllers, a control program may consist of zero or more function blocks. Many of the main types of function blocks mostly work based on timers, therefore, timing requirements in terms of response time or time-out are essential parts of the performance-related requirements in real-time control programs.