What is a scheduler?
There are two ways of viewing a scheduler:
● At one level, a scheduler can be viewed as a simple operating system that allows tasks to be called periodically or (less commonly) on a one-shot basis.
● At a lower level, a scheduler can be viewed as a single timer interrupt service routine that is shared between many different tasks. As a result, only one timer needs to be initialized, and any changes to the timing generally requires only one function to be altered. Furthermore, we can generally use the same scheduler whether we need to execute one, ten or 100 different tasks. Note that this ‘shared ISR’ is very similar to the shared printing facilities (for example) provided by a desktop OS.
For example, Listing 13.6 shows how we might schedule the three tasks shown in Listing 13.5, this time using a scheduler.
