1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

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

    12 <concept id="GUID-C244D421-8BD0-4212-A5C5-47A8B1E0C1E2" xml:lang="en"><title>Kernel

    13 Extension</title><shortdesc>This document describes how to implement a device driver as a kernel

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

    15 <section id="GUID-D3EEB917-368E-45A3-866E-C63490994C59">             <p>Device

    16 drivers can also be kernel extensions, which means that they are loaded by

    17 the Kernel when it boots. They are used for extending the Kernel, as the name

    18 suggests. Generally, kernel extensions provide early initialisation of devices

    19 that must be permanently available, such as LCD, DMA, and I2C and other peripheral

    20 bus controllers. Because kernel extensions are loaded by the Kernel, they

    21 are never unloaded and so their destructors are never called. </p> <p>The <codeph>DECLARE_STANDARD_EXTENSION</codeph> macro

    22 is used to provide an entry point for a kernel extension (see <xref href="GUID-B94FFCA4-1EB3-46A7-9FF9-54C55D67FFE8.dita">Entry

    23 Points</xref>). </p> <p>Extensions are built into the ROM image, by specifying

    24 the <codeph>extension</codeph> keyword in the <filepath>.iby</filepath> file.

    25 This enables the ROM build tool to build the ROM header. The extensions are

    26 loaded in the order specified in the <filepath>kernel.iby</filepath> file. </p> <codeblock id="GUID-1AABD1B3-BF5A-50FC-9B1F-86E657F9890D" xml:space="preserve">extension[VARID]=\Epoc32\Release\&lt;assp&gt;\urel\KDEBUG.DLL \System\Bin\kdebug.dll</codeblock> <p>A

    27 kernel extension's interface to other Kernel side components is usually exported

    28 using a static interface. Clients can access this interface by using the global

    29 instance of the object created and initialised in the <codeph>DECLARE_STANDARD_EXTENSION</codeph> entry

    30 point. They then use this object to call the exported API. </p> <p>Kernel

    31 extensions can also be implemented that let user code open channels on them

    32 to use the interface. This model is used for devices where initialisation

    33 has to be done at system boot up, but which can then be used by the clients,

    34 for example, the media driver <filepath>elocd.ldd</filepath>. </p> <p>To do

    35 this, drivers have to declare <xref href="GUID-38771B51-195D-3148-A462-277DA3696117.dita"><apiname>DECLARE_EXTENSION_LDD</apiname></xref> in

    36 addition to the <xref href="GUID-8B6DF6D7-4995-3564-9303-272500D7E747.dita"><apiname>DECLARE_STANDARD_EXTENSION</apiname></xref> macro. In this

    37 model, extensions generally call <xref href="GUID-671F731F-428F-379D-8260-D9F18CAC25CF.dita#GUID-671F731F-428F-379D-8260-D9F18CAC25CF/GUID-ADB60188-13D4-3245-96D0-4D44CB983551"><apiname>Kernel::InstallLogicalDevice()</apiname></xref> /<xref href="GUID-671F731F-428F-379D-8260-D9F18CAC25CF.dita#GUID-671F731F-428F-379D-8260-D9F18CAC25CF/GUID-703E2FAD-A71C-377B-86F0-D19643D4CDA9"><apiname>Kernel::InstallPhysicalDevice()</apiname></xref> to

    38 install the logical device. Later clients can open channels on this driver

    39 and use the interface in the same way as a standard driver. </p> <codeblock id="GUID-29B10898-2CCA-5D03-B14A-CAD3C56EB73F" xml:space="preserve">DECLARE_STANDARD_EXTENSION()

    40     {

    41     ...

    42     // Create factory object

    43     DExDriverLogicalDevice* device = new DExDriverLogicalDevice;

    44     if (device==NULL)

    45         r=KErrNoMemory;

    46     else

    47         {

    48         // Installs the logical device by calling the second

    49         // phase constructor

    50         r=Kern::InstallLogicalDevice(device);

    51         }

    52     return r;

    53     }

    54 

    55 DECLARE_EXTENSION_LDD()

    56     {

    57     return new DExDriverLogicalDevice;

    58     }</codeblock>     </section>

    59 </conbody></concept>