TABLE OF CONTENTS Dividing a program into several component tasks increases the complexity of the implementation. But a full multi-tasking application does offer several advantages to the systems developer which are described in this chapter. Most real-time, multi-tasking applications employ pre-emptive scheduling, and thus the need to protect critical data arises. The different multi-tasking environments are described.
The most likely situation that demands a multi-tasking solution is where there are several rather unpredictable input/output activities which need to be handled at the same time as some core processing. If the equipment includes a user front panel keyboard and display, special device interaction, intermittent LAN comms and critical control activity, then perhaps a programmer's mind turns to a multi-tasking solution. In part, this is to defer until run-time some important decisions about code sequencing, and then delegate responsibility for it down to the RTE! Although the programmer could serialize all these activities by using test-and-skip operations in a single loop, such a crude scheme suffers from increasing disadvantages as the systems grows in size and the relative demands of each of the component activities varies. Perhaps even more significant than the provision of convenient demand-driven code sequencing is the influence that multi-tasking can exert on system design. Design methods that support the decomposition of problems into multiple, semi-independent tasks for concurrent processing offer a straightforward method for dealing with complexity. In this way, big systems can be handled by partitioning them into many smaller, separately...
