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<concept id="GUID-9E7F8D0B-2B0E-41CC-BCDF-6B01B56CEF37" xml:lang="en"><title>Debounce

Functions</title><shortdesc>Describes the debounce functions involved in implementing the Symbian

platform GPIO class.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>Debouncing means filtering out distortions of the signal caused, for instance,

by physical pressure on a key. Some platforms provide hardware mechanisms

for debouncing, otherwise implementers must provide for debouncing by software.

Both hardware and software debouncing involve sampling the signal at a specified

interval. The Symbian platform GPIO class provides a function <xref href="GUID-837F3EC5-5379-3B88-B27B-A092E9F2E422.dita"><apiname>SetDebounceTime()</apiname></xref> to

supply that interval but does not impose any restrictions on the implementation.

Software debouncing can be performed at the level of the pin rather than the

module, and this is strongly recommended where debouncing is performed by

software.  </p>

<section id="GUID-718F1593-206E-4738-A34A-C9D3F52063EE"><title>Implement the

debounce functions</title> <ul>

<li><p>          Implement <xref href="GUID-837F3EC5-5379-3B88-B27B-A092E9F2E422.dita"><apiname>SetDebounceTime()</apiname></xref> with return

value          <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.         </p> <p>          Verify

that the platform supports debouncing either by hardware          or software.

Use the passed in value as the sampling interval in milliseconds.         </p> <p> 

        Only implement this if the platform supports debouncing.         </p> </li>

<li><p>          Implement <xref href="GUID-72F9F470-4815-3674-A90F-1038C565F2E0.dita"><apiname>GetDebounceTime()</apiname></xref> with return

         value <xref href="GUID-6CA4F1ED-7947-3087-B618-D35858FAA3BC.dita"><apiname>KErrNone</apiname></xref>.         </p> <p>          Determine

value in milliseconds of the sampling interval used in          debouncing

and set aTime to that value.         </p> <p>          Only implement this

if the platform supports debouncing.         </p> </li>

<li><p>          Implement these functions with return value          <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>.

        </p> <ul>

<li><p>                <xref href="GUID-837F3EC5-5379-3B88-B27B-A092E9F2E422.dita"><apiname>SetDebounceTime() </apiname></xref>              </p> </li>

<li><p>                <xref href="GUID-72F9F470-4815-3674-A90F-1038C565F2E0.dita"><apiname>GetDebounceTime()</apiname></xref>              </p> </li>

</ul> <p>          Return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref> if the pin does

not          support debouncing.         </p> </li>

</ul> </section>

</conbody></concept>