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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-BAE9F3A8-E232-491B-9F29-E2BF7298F9EA" xml:lang="en"><title>Trigger
Functions</title><shortdesc>Describes the trigger functions involved in implementing the Symbian
platform GPIO class.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>A trigger is the electrical waveform which signals an interrupt and sometimes
a wakeup. Triggers are detected either by their level (high or low) or by
their edge (rising, falling or both). When you associate an interrupt with
a trigger you must specify the type (level or edge) and then the subtype.
Some configurations of type and subtype are incompatible, for instance level
trigger with rising edge. The Symbian platform GPIO class specifies the possible
combinations in the enumeration <xref href="GUID-D5CB424B-03D4-3755-9DEB-A6A9988CACE1.dita"><apiname>TGpioDetectionTrigger</apiname></xref>.
It is for the implementation to check that a given pin supports a consistent
configuration.   </p>
<section id="GUID-505B2E66-80A7-423D-8BE9-D5325D02F006"><title>Implement the
trigger functions</title> <ul>
<li><p>          Implement <xref href="GUID-29000C80-F7B6-3B7C-8944-F6BCAE2B6618.dita"><apiname>SetInterruptTrigger()</apiname></xref> with return
         value <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.         </p> <p>          Verify
that the pin is being used as an interrupt source and that          there
is an ISR bound to it. Set the interrupt trigger on the specified pin.   
     </p> </li>
<li><p>          Implement <xref href="GUID-29000C80-F7B6-3B7C-8944-F6BCAE2B6618.dita"><apiname>SetInterruptTrigger()</apiname></xref> with return
         value <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>.         </p> <p>     
    Return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref> if the pin does not       
  support interrupts.         </p> </li>
<li><p>          Implement <xref href="GUID-28F2D8DB-5D57-3199-9066-1B0252EE632E.dita"><apiname>SetWakeupTrigger()</apiname></xref> with return
         value <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.         </p> <p>          Verify
that the pin is being used as an interrupt source and that          there
is an ISR bound to it. Set the interrupt trigger on the specified pin.   
      The trigger should probably be edge detected.         </p> </li>
<li><p>          Implement <xref href="GUID-28F2D8DB-5D57-3199-9066-1B0252EE632E.dita"><apiname>SetWakeupTrigger()</apiname></xref> with return
         value <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>.         </p> <p>     
    Return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref> if the pin does not       
  support wakeups.         </p> </li>
</ul>  </section>
</conbody></concept>