A data acquisition and display application in which readings are periodically taken and displayed is an example of a soft real-time application. Although there may be a desired sample and display rate of 500 ms, errors will not result if the sample rate is not accurately met. The worst that can happen is that samples are not displayed as quickly as desired, but the point is that no errors can result. Multi-tasking is typically done using the cyclical executive approach or a variation thereof. These features will be elaborated upon below.
Predictability Consider the automotive example given above.
The total processing time must be less than 50 ms, or the system requirements will not be met. Item 2 is a bit more difficult to compute. We can contact the kernel supplier and ask them, but this will still be inaccurate, since the actual time is processor, clock, and hardware dependent. The easiest thing to do is to run the software, and see if it gets the job done within the 50 ms window. The key point to be understood is that item 2 must be predictable and repeatable, otherwise, a worst case time for item 2 cannot be known, and the system may or may not work properly.