4.3 Cooperative Multitasking
Cooperative multitasking is a convenient way to perform several different tasks at the same time. An example would be to step a machine through a sequence of steps and at the same time independently carry on a dialog with the operator via a human interface. Coop- erative multitasking differs from a different approach called preemptive multitasking. Dynamic C supports both types of multitasking. In cooperative multitasking each separate task voluntarily surrenders its compute time when it does not need to perform any more activity immediately. In preemptive multitasking control is forcibly removed from the task via an interrupt.
Dynamic C has language extensions to support multitasking. The major C constructs are called costatements, cofunctions, and slicing. These are described more completely in the Dynamic C User’s Manual. The example below, sample program DEMOJR3.C, uses cos- tatements. A costatement is a way to perform a sequence of operations that involve pauses or waits for some external event to take place. A complete description of costatements is in the Dynamic C User’s Manual. The DEMOJR3.C sample program has two independent tasks. The first task flashes LED DS4 once a second. The second task uses button S1 on the Prototyping Board to toggle the logical value of a virtual switch, vswitch, and flash DS1 each time the button is pressed. This task also debounces button S1.
48 | Jackrabbit (BL1800) |
