November 22nd, 2016 by
A real-time operating system has certain distinguishing characteristics. The term is used ambiguously due to the varying time constraints for real-time systems. For instance, a real-time system needs an application to meet the average deadlines of a set time with minimal variability while processing an external event. This can be the case for heating process, mixing control or display processes. On the other hand, time deadlines for a critical real-time system are very strict. These deadlines must be met in every case. An example of such a case is when a controlled radiation dose has to be delivered to a sample.
A critical real-time system requires adequate time for processing an external stimulus. This is known as the response time and it lies within a predetermined value in all possible situations. Basically, a real-time system is characterized by correctness that involves both the logical outputs correctness and timeliness.
To understand these characteristics of RTOS, it is important to consider one of its applications. A good example is a process that involves, mixing and heating followed by mixing of the sample in the food production unit or laboratory. The duration taken to mix and heat the ingredients may not need to be timed precisely. However, it is important that the processes order remains correct throughout. On the other hand, if high-throughput screening process is controlled by automation equipment where the samples degrade within a pre-determined time, a higher precision level will most probably be required.
Clearly, time constraints are what distinguish real-time operating systems. These systems can be soft, firm or hard systems. In a hard real-time system, if time constraints are not met, system failure occurs. In a firm real-time system, time constraints have to be met in a majority of cases. However, missing few deadlines can be tolerated. With a soft real-time system, there is a degradation of performance with any failure to meet time constraints. However, a catastrophic failure of the system will not occur.
Usually, some ordinary OS with real-time features can be used in soft and firm real-time applications. However, RTOS’s are mostly necessary in hard real-time systems. The choice of an operating system plays a very critical role in the design of an application as well as how time constraints of an application are met. That’s why it is very important to understand the characteristics of a real-time operating system in order to determine whether it is appropriate for your application.