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19.6 接口中的任务与函数</div>
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Tasks and functions can be defined within an interface, or they can be defined within one or more of the modules connected. This allows a more abstract level of modeling. For example “read” and “write” can be defined as tasks, without reference to any wires, and the master module can merely call these tasks. In a modport these tasks are declared as import tasks. </p>
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If a module is connected to a modport containing an exported task or function, and the module does not define that task or function, then an elaboration error shall occur. Similarly if the modport contains an exported task or function prototype, and the task or function defined in the module does not exactly match that prototype, then an elaboration error shall occur. </p>
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If the tasks or functions are defined in a module, using a hierarchical name, they must also be declared as extern in the interface, or as export in a modport. </p>
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Tasks (not functions) can be defined in a module that is instantiated twice, e.g. two memories driven from the same CPU. Such multiple task definitions are allowed by a forkjoin extern declaration in the interface.</p></div>
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<a href="00227.html" target="topic">19.6.1 An example of using tasks in an interface</a> </div></td><td class="Element206" valign="top" width="50%">
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<a href="00228.html" target="topic">19.6.2 An example of using tasks in modports</a> </div></td><td class="Element206" valign="top" width="50%">
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This interface example shows how to use modports to control signal directions and task access in a full read/write interface. </div></td></tr><tr>
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<a href="00229.html" target="topic">19.6.3 An example of exporting tasks and functions</a> </div></td><td class="Element206" valign="top" width="50%">
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This interface example shows how to define tasks in one module and call them in another, using modports to control task access. </div></td></tr><tr>
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It is normally an error for more than one module to export the same task name. However, several instances of the same modport type can be connected to an interface, such as memory modules in the previous example. So that these can still export their read and write tasks, the tasks must be declared in the interface using the extern forkjoin keywords.<br><br>The call to extern forkjoin task countslaves( ); in the example below behaves as: </div></td></tr></table></div></div>
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