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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-5471CDD4-030E-4509-8B7C-603C9B7953B4" xml:lang="en"><title>GPIO

    13 Technology Guide</title><shortdesc>Discusses GPIO technology as specified for implementation as a

    14 SHAI.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <section id="GUID-087A2FDD-8879-5944-9C0E-05ABD9FFAF50"><title>Purpose</title><p>GPIO

    16 (General Purpose Input/Output) is a communication interface between microprocessor

    17 components. GPIOs consist of binary inputs/outputs called pins, arranged in

    18 groups called modules, typically of up to 32 pins in a module. GPIO is often

    19 used to implement hardware interrupts and CPU wakeup and also to control peripherals. </p> <p>Symbian

    20 platform defines a single static exported class <xref href="GUID-C93C53D3-2BE8-36AE-83B8-4CDB4195649B.dita"><apiname>GPIO</apiname></xref> for

    21 device drivers to use to access the GPIO hardware on the device. The SHAI

    22 does not provide an implementation of the class. When you implement a board

    23 support package for device hardware with GPIO hardware, you should provide

    24 an implementation of the class in a variant-specific component. </p> </section>

    25 <section id="GUID-48176C53-72DC-5A2E-8124-9FA222AE91AB"><title>Key concepts</title> <p>Certain

    26 terms have a specific meaning in the context of GPIO. </p> <dl>

    27 <dlentry>

    28 <dt>module</dt>

    29 <dd><p>A group of pins which can be mapped on to a register. </p> </dd>

    30 </dlentry>

    31 <dlentry>

    32 <dt>function</dt>

    33 <dd><p>The purpose for which the pins and modules are used. GPIO is one such

    34 purpose: serial bus line signals are an example of a different function. </p> </dd>

    35 </dlentry>

    36 <dlentry>

    37 <dt>state</dt>

    38 <dd><p>Electrical states as mapped on to mode, direction and logical state. </p> </dd>

    39 </dlentry>

    40 <dlentry>

    41 <dt>configuration</dt>

    42 <dd><p>The current configuration of all the pins on a module: their direction,

    43 electrical and logical state, interrupt and wakeup enablement status. </p> </dd>

    44 </dlentry>

    45 </dl> </section>

    46 <section id="GUID-35C041B8-F3F0-544B-A67E-0A25BE140D8B"><title>Design features</title> <p>The

    47 Symbian platform GPIO interface reserves most decisions about design to implementers

    48 in accordance with the platform they are writing for. However, certain design

    49 features are implicit in the interface provided. </p> <p>These are the main

    50 features of the Symbian platform GPIO interface: </p> <ul>

    51 <li id="GUID-DD56DA4D-C0A7-5180-9142-81887C7538C2"><p>The interface is supplied

    52 as a single static exported interface to be implemented as a variant specific

    53 component. </p> </li>

    54 <li id="GUID-B201623E-64E2-5FEF-959F-9C096F424D7E"><p>The access APIs are

    55 specified at pin level. There are no module level APIs. </p> </li>

    56 <li id="GUID-D8FF221C-F0EB-5F1B-886B-0F6AAC4023A9"><p>The pin IDs are to be

    57 defined in a single enumeration with values to be determined at build time. </p> </li>

    58 <li id="GUID-7F703C00-FE1D-5DE6-8E0E-29E4138E1060"><p>Bidirectional input/output

    59 is not supported. </p> </li>

    60 <li id="GUID-2CF55AD5-B98C-5207-A78F-B4C7654E677A"><p>Electrical states intermediate

    61 between High and Low are not supported. </p> </li>

    62 <li id="GUID-C3982CA3-04F3-58C4-B907-EE6A82FBD548"><p>It is strongly recommended

    63 that debouncing should be implemented in software if it is not provided with

    64 the hardware. </p> </li>

    65 <li id="GUID-CD64A653-AB5C-575A-A3D3-0151FD8ADCF4"><p>There is limited support

    66 for extensions to the functionality within the framework of the static interface. </p> </li>

    67 </ul> </section>

    68 </conbody></concept>