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<concept id="GUID-6A4FE3A3-2E5D-51BB-8272-5995586291E9" xml:lang="en"><title>LCD

Extension Implementation Tutorial</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>This topic describes how to create an LCD Extension. </p>

<p>The topic uses a reference board port named <filepath>template_variant</filepath> as

an example implementation. </p>

<section id="GUID-7DDD91D2-A69F-4940-AA58-74EB2A989E55"><title>Build environment</title> <p>In the template reference board

port, the <filepath>.mmp</filepath> file for the LCD Extension is <filepath>...\template_variant\lcdtemplate.mmp</filepath>.

This is one of the <codeph>PRJ_MMPFILES</codeph> referenced in the template

variant's <filepath>bld.inf</filepath> file in the <filepath>...\template_variant\...</filepath> directory,

and means that the LCD Extension is built as part of the Variant. </p> <p>The

source for the driver is contained entirely within <filepath>...\template_variant\specific\lcd.cpp</filepath>. </p> <p>The

driver is defined as a kernel extension and is loaded early in the boot sequence. </p> </section>

<section id="GUID-FC49B296-5DFA-4C19-BEDE-F641D70E5ED9"><title>Initialization</title> <p>The driver functionality is almost

entirely encapsulated by the <codeph>DLcdPowerHandler</codeph> class. This

is a power handler class derived from <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref>. An

instance of <codeph>DLcdPowerHandler</codeph> is created when the extension

is loaded. </p> <p> <codeph>DLcdPowerHandler</codeph> is defined within the

source file itself <filepath>...\template_variant\specific\lcd.cpp</filepath>. </p> <p>As

the driver is a kernel extension, it must have a <codeph>DECLARE_STANDARD_EXTENSION()</codeph> statement.

In the template port, this is implemented as follows: </p> <codeblock id="GUID-BB93E7E7-06DA-5A12-ABA1-D07AA246D6FC" xml:space="preserve">DECLARE_STANDARD_EXTENSION()

    {

    __KTRACE_OPT(KPOWER,Kern::Printf("Starting LCD power manager"));

    // create LCD power handler

    TInt r=KErrNoMemory;

    DLcdPowerHandler* pH=new DLcdPowerHandler;

    if (pH)

        r=pH->Create();

    __KTRACE_OPT(KPOWER,Kern::Printf("Returns %d",r));

    return r;

    }

</codeblock> <p>This simply creates an instance of the <codeph>DLcdPowerHandler</codeph> class

and then calls its <codeph>Create()</codeph> function which implements the

display setup. This function should do the following: </p> <ul>

<li id="GUID-4D3B36C6-C782-5B3F-8244-7FD33B9976C6"><p>map the video RAM </p> </li>

<li id="GUID-B693BD2B-50FF-554D-AF2B-1992A472F586"><p>setup the video info

structure </p> </li>

<li id="GUID-1DF67FC0-90FA-5853-88C2-6DBA5C60F377"><p>install the HAL handler </p> </li>

<li id="GUID-2B8080C4-2A9F-5AA2-B609-3DC8F5759DDE"><p>install the power handler. </p> </li>

</ul> <p><b> Map

the video RAM</b> </p> <p>The frame buffer is a <xref href="GUID-2A34A3DD-A7FE-34A0-B0B7-BB0A4F04B098.dita"><apiname>DPlatChunkHw</apiname></xref> object,

and should be mapped as globally accessible, readable and writeable. It should <i>not</i> be

mapped as writeback cached, it should be either not-cached or write-through.

The advantage of write through is that it allows the use of the write buffer. </p> <codeblock id="GUID-148795D9-45A2-526B-A2F7-57B5B2AAC8AB" xml:space="preserve">TInt DLcdPowerHandler::Create()

    {

    ...

    // map the video RAM

    TInt vSize = ((TemplateAssp*)Arch::TheAsic())->VideoRamSize();

    ivRamPhys = TTemplate::VideoRamPhys();                // EXAMPLE ONLY: assume TTemplate interface class

    TInt r = DPlatChunkHw::New(iChunk,ivRamPhys,vSize,EMapAttrUserRw|EMapAttrBufferedC);

    if ® != KErrNone)

        return r;

 ...

</codeblock> <p>If the frame buffer resides in main RAM and there is no restriction

on which physical addresses may be used for it, physical RAM for the frame

buffer should be reserved by using <xref href="GUID-3DC7B5F2-512E-3FF3-BC08-945DDE2AE680.dita#GUID-3DC7B5F2-512E-3FF3-BC08-945DDE2AE680/GUID-B506D835-505D-3D89-A840-475F291908DC"><apiname>Epoc::AllocPhysicalRam()</apiname></xref>. </p> <p>If

the frame buffer does not reside in main RAM, there is no problem about reserving

it. </p> <p>If the frame buffer must reside at a specific address in main

RAM, there are two strategies available for reserving it: </p> <ul>

<li id="GUID-29D3BF5F-442B-5912-A8B9-4F1F76C1879E"><p>If no conflicts are

permitted between the frame buffer and memory allocations made during the

kernel boot (for example, if the frame buffer must reside at the end of main

memory), simply use <xref href="GUID-3DC7B5F2-512E-3FF3-BC08-945DDE2AE680.dita#GUID-3DC7B5F2-512E-3FF3-BC08-945DDE2AE680/GUID-78F136DC-023B-30AB-A1AB-34D6BC4F1B3E"><apiname>Epoc::ClaimPhysicalRam()</apiname></xref>. This function

just marks a region of physical RAM as allocated, returning an error if any

part of the region has already been used. </p> </li>

<li id="GUID-F2C5ED3A-767A-58CA-BDC6-78D3C1820C80"><p>The required physical

RAM region can be reserved in the bootstrap. The correct place to do this

is in the implementation of the boot table function <xref href="GUID-B3F6FC45-3BF0-5F92-8325-44C705BA47AE.dita#GUID-B3F6FC45-3BF0-5F92-8325-44C705BA47AE/GUID-B3C6ACE9-A803-59D4-8EBD-314363905427">BTF_Reserve</xref> when writing platform-specific source code for the bootstrap.

See the Bootstrap <xref href="GUID-5EB03086-A87D-5588-8927-7A7F8DB38366.dita">Port

Implementation Tutorial</xref> for more detail and look at <filepath>...\template_variant\bootstrap\template.s</filepath> for

a concrete example. </p> </li>

</ul> <p>Note that all Symbian platform base ports currently create a second

frame buffer for a secure screen. However, as platform security is not yet

implemented, this is wasteful of RAM and should be omitted. </p> <p id="GUID-57223C8C-0381-51AC-8E8A-771434136A5C"><b> Set up the video information

structure</b> </p> <p>The video information structure is used to define several

aspects of the display including display size, bits per pixel and address

of the frame buffer. This structure is the class <xref href="GUID-C4712A78-6C58-39ED-AF84-11038DB8571D.dita"><apiname>TVideoInfoV01</apiname></xref> defined

in the header file <filepath>...\eka\include\videodriver.h</filepath> and

exported to <filepath>...\epoc32\include</filepath>. </p> <codeblock id="GUID-0680E467-9552-5FD6-BBDE-60AE95F0B941" xml:space="preserve">TInt DLcdPowerHandler::Create()

    {

       ...

       // setup the video info structure, this will be used to remember the video settings

       iVideoInfo.iDisplayMode = KConfigLcdInitialDisplayMode;

       iVideoInfo.iOffsetToFirstPixel = Lcd_Mode_Config[KConfigLcdInitialDisplayMode].iOffsetToFirstVideoBuffer;

       iVideoInfo.iIsPalettized = Lcd_Mode_Config[KConfigLcdInitialDisplayMode].iIsPalettized;

       iVideoInfo.iOffsetBetweenLines = Lcd_Mode_Config[KConfigLcdInitialDisplayMode].iOffsetBetweenLines;

       iVideoInfo.iBitsPerPixel = Lcd_Mode_Config[KConfigLcdInitialDisplayMode].iBitsPerPixel;

       iVideoInfo.iSizeInPixels.iWidth = KConfigLcdWidth;

       iVideoInfo.iSizeInPixels.iHeight = KConfigLcdHeight;

       iVideoInfo.iSizeInTwips.iWidth = KConfigLcdWidthInTwips;

       iVideoInfo.iSizeInTwips.iHeight = KConfigLcdHeightInTwips;

       iVideoInfo.iIsMono = KConfigLcdIsMono;

       iVideoInfo.iVideoAddress=(TInt)pV;

       iVideoInfo.iIsPixelOrderLandscape = KConfigLcdPixelOrderLandscape;

       iVideoInfo.iIsPixelOrderRGB = KConfigLcdPixelOrderRGB;

    ...

    }</codeblock> <p><b> Install

the HAL handler</b> </p> <p>Control of the display is done by using the HAL,

the Hardware Abstraction Layer. </p> <p>The <codeph>DLcdPowerHandler</codeph> class

provides the implementation for the HAL handler for the HAL function group <xref href="GUID-7F299BFC-D8A5-3A5A-B8DA-39BF42C99DC6.dita"><apiname>EHalGroupDisplay</apiname></xref> and

this needs to be registered with the kernel by calling <xref href="GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D.dita#GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D/GUID-8C8DCE9D-0094-3909-8FDA-2F3134D0BC88"><apiname>Kern::AddHalEntry()</apiname></xref>. </p> <codeblock id="GUID-F9E86404-742D-5931-BA77-DA246A3975E5" xml:space="preserve">TInt DLcdPowerHandler::Create()

    {

       ...

       // install the HAL function

       r=Kern::AddHalEntry(EHalGroupDisplay, halFunction, this);

       if (r!=KErrNone)

              return r;

    ...

    }</codeblock> <p>See <xref href="GUID-2D977A02-5928-5441-8AE7-42A722F2A4B8.dita#GUID-2D977A02-5928-5441-8AE7-42A722F2A4B8/GUID-4DA41221-40B9-5BC7-B2C6-7C6EB4522508">User-Side

Hardware Abstraction</xref> for more detailed information on the HAL. </p> <p><b> Install the power handler</b> </p> <p>A call must be made to the <codeph>Add()</codeph> function,

which is supplied by the <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref> base class of <codeph>DLcdPowerHandler</codeph>,

to register the handler with the power manager. </p> <codeblock id="GUID-9286C3A2-DC2B-54F1-9F28-4EBE085AEE84" xml:space="preserve">TInt DLcdPowerHandler::Create()

    {

       ...

        // install the power handler

        // power up the screen

        Add();

    ...

    }</codeblock> </section>

<section id="GUID-85B93308-2EDF-462C-8F64-6AE40B8B16B6"><title>HAL handler implementation</title> <p>Requests to get and

set hardware attributes are made through calls to <xref href="GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8.dita#GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8/GUID-573C49D6-7763-37AE-B2B2-4C8FB1327E21"><apiname>HAL::Get()</apiname></xref> and <xref href="GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8.dita#GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8/GUID-9454F1B2-D525-3D6D-A872-C6457CACD4FC"><apiname>HAL::Set()</apiname></xref>.

These two HAL functions take a value that identifies a hardware attribute,

one of the <xref href="GUID-8BE90160-2C60-3582-82C8-4A108C7C0317.dita#GUID-8BE90160-2C60-3582-82C8-4A108C7C0317/GUID-1959915A-BA99-3F94-AFD4-FD1AA540BFBF"><apiname>HALData::TAttribute</apiname></xref> values. </p> <p>For the

LCD Extension, the relevant hardware attributes are: <codeph>EDisplayMode</codeph>, <codeph>EDisplayBitsPerPixel</codeph>, <codeph>EDisplayIsPalettized</codeph>, <codeph>EDisplayIsMono</codeph>, <codeph>EDisplayMemoryAddress</codeph>, <codeph>EDisplayMemoryHandle</codeph>, <codeph>EDisplayOffsetToFirstPixel</codeph>, <codeph>EDisplayOffsetBetweenLines</codeph>, <codeph>EDisplayXPixels</codeph>, <codeph>EDisplayYPixels</codeph>, <codeph>EDisplayPaletteEntry</codeph> and <codeph>EDisplayOffsetBetweenLines</codeph>. </p> <p>The HAL handler

is registered with the kernel as the handler for the <xref href="GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7.dita#GUID-66A851A0-2A0C-3624-AEC1-22F6629FABF7/GUID-950EA0D3-747F-305E-92EA-1579023A111E"><apiname>THalFunctionGroup::EHalGroupDisplay</apiname></xref> group.

The HAL handler itself takes a function ID, which is one of the <xref href="GUID-BB011D9B-105F-345C-9FC0-39B0BA509394.dita"><apiname>TDisplayHalFunction</apiname></xref> enumerators. </p> <p>A

call to <xref href="GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8.dita#GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8/GUID-573C49D6-7763-37AE-B2B2-4C8FB1327E21"><apiname>HAL::Get()</apiname></xref> and <xref href="GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8.dita#GUID-BD00E7FC-C234-3111-87A5-10F79EB0F2B8/GUID-9454F1B2-D525-3D6D-A872-C6457CACD4FC"><apiname>HAL::Set()</apiname></xref> that

takes one of the hardware attributes relevant to the LCD Extension is ultimately

routed to a call to this HAL handler function passing an appropriate function

ID. The association between the hardware attribute and the function ID is

the responsibility of the accessor functions. </p> <p>See <xref href="GUID-2D977A02-5928-5441-8AE7-42A722F2A4B8.dita#GUID-2D977A02-5928-5441-8AE7-42A722F2A4B8/GUID-4DA41221-40B9-5BC7-B2C6-7C6EB4522508">User-Side Hardware Abstraction</xref> for more information on the way this

works in general. </p> <p>The HAL handler is implemented as a case statement,

switching on the function ID. For example, the following code fragment taken

from <codeph>DLcdPowerHandler::HalFunction()</codeph> gets and sets the brightness: </p> <codeblock id="GUID-41D5153A-107A-5FCC-9E51-C6250857F3AC" xml:space="preserve">TInt DLcdPowerHandler::HalFunction(TInt aFunction, TAny* a1, TAny* a2)

    {

    TInt r=KErrNone;

    switch(aFunction)

        {

        ...

         case EDisplayHalSetDisplayBrightness:

             if(!Kern::CurrentThreadHasCapability(ECapabilityWriteDeviceData,

       __PLATSEC_DIAGNOSTIC_STRING("Checked by Hal function EDisplayHalSetDisplayBrightness")))

                       return KErrPermissionDenied;

             r=SetBrightness(TInt(a1));

             break;

         case EDisplayHalDisplayBrightness:

             kumemput32(a1,&iBrightness,sizeof(iBrightness));

             break;

        ...

</codeblock> <p>where <codeph>SetBrightness()</codeph> is implemented as: </p> <codeblock id="GUID-82F38251-19A9-54BC-A066-80ED5AC549AF" xml:space="preserve">TInt DLcdPowerHandler::SetBrightness(TInt aValue)

    {

     __KTRACE_OPT(KEXTENSION,Kern::Printf("SetBrightness(%d)", aValue));

     if (aValue >= KConfigLcdMinDisplayBrightness && aValue <= KConfigLcdMaxDisplayBrightness)

         {

         iBrightness=aValue;

         // TO DO: (mandatory)

         // set the brightness

         //

         return KErrNone;

         }

    return KErrArgument;

    }

</codeblock> <p>If an attribute does not have an implementation, the HAL handler

function should return <xref href="GUID-F89DA3F0-2A48-3F9B-8F08-29350E92D0E4.dita"><apiname>KErrNotSupported</apiname></xref>. </p> <p>For platform

security, the code only allows the attribute to be set if the current thread

has been authorized to write system data. Otherwise, it returns <xref href="GUID-213DE05E-24F7-3E94-9B35-F4A72B3EBFD8.dita"><apiname>KErrPermissionDenied</apiname></xref>. </p> <p><b>Switch on and switch off operations</b> </p> <p>All of the HAL operations

are seen to be synchronous by the user side. However there are some operations

such as turning the display on and off which may need to be implemented asynchronously. </p> <p>The

display on/off code is implemented using synchronous kernel-side messages.

There is only one message per thread and the thread always blocks while a

message is outstanding. This means it is possible to make an asynchronous

operation appear synchronous. </p> <p>When turning on the screen the kernel-side

message is queued and this thread is blocked until the message is completed,

which happens when the display has been turned on. </p> <p>If a display needs

to be turned on and off truly asynchronously (for example, if millisecond

timer waits are required during the process of turning on the display), the

above functionality must be changed so that the complete occurs when the display

is truly on. </p> <p><b>Accessing

the video information structure</b> </p> <p>When any part of the <xref href="GUID-6A4FE3A3-2E5D-51BB-8272-5995586291E9.dita#GUID-6A4FE3A3-2E5D-51BB-8272-5995586291E9/GUID-57223C8C-0381-51AC-8E8A-771434136A5C">video information structure</xref> is read or written to, this must be done

within a critical section to prevent potential collisions with other threads

attempting to access the structure concurrently. A fast mutex is used to ensure

that only one thread can access the video information at any one time, as

the code segment below shows. </p> <codeblock id="GUID-E30D9790-109C-541F-A534-C92CBD4E1706" xml:space="preserve">TInt DLcdPowerHandler::GetCurrentDisplayModeInfo(TVideoInfoV01&amp; aInfo, TBool aSecure)

    {

     __KTRACE_OPT(KEXTENSION,Kern::Printf("GetCurrentDisplayModeInfo"));

     NKern::FMWait(&iLock);

     if (aSecure)

          aInfo = iSecureVideoInfo;

     else

         aInfo = iVideoInfo;

     NKern::FMSignal(&iLock);

     return KErrNone;

     }

</codeblock> </section>

<section id="GUID-04C06DAE-EE8E-4EE9-940F-807F82FBACD1"><title>Power handler implementation</title> <p>The <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref> class

defines the interface that the driver must implement to provide power handling

behaviour. For the template reference board, the LCD Extension defines and

implements the <codeph>DLcdPowerHandler</codeph> class derived from <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita"><apiname>DPowerHandler</apiname></xref>. </p> <p> <b>Note</b>: </p> <ul>

<li id="GUID-32D95977-F46B-50E0-B575-BE7369C05F62"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-578DB5FB-731D-36B2-A459-AAC7F250D726"><apiname>DPowerHandler::PowerDown()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-DDC564B4-BD12-30E9-B04A-DBA6CFAF8743"><apiname>DPowerHandler::PowerUp()</apiname></xref>  </p> <p>These functions are called in the context of the thread that initiates

power down or power up, and synchronization is required, typically by means

of power up and power down DFCs. </p> </li>

<li id="GUID-7DC988A6-C60E-5951-9DD7-82DA129A8CB6"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-038F9D7D-7DA0-3299-8AA2-85F175206887"><apiname>DPowerHandler::PowerUpLcd()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-6EAF00D1-3CBA-3BC0-BAD9-7301EE5F9E12"><apiname>DPowerHandler::PowerDownLcd()</apiname></xref>  </p> <p>These functions generally queue DFCs which then call platform-specific

functions to power the display up and down. </p> </li>

<li id="GUID-51152EA7-C1A5-5AB3-8ACD-6FF6F16A255D"><p> <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-BF62042B-FB7B-3D5B-8379-490FBA284A7A"><apiname>DPowerHandler::PowerUpDone()</apiname></xref> and <xref href="GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7.dita#GUID-761AE02B-41A6-35EA-AA9F-0AEEFF67A6F7/GUID-EBE8CFF8-50BD-3AC3-A4C8-47094DA5674D"><apiname>DPowerHandler::PowerDownDone()</apiname></xref>  </p> <p>When power up or down is complete, the interface supplies a set

of acknowledgment functions which must be called when the change of state

has taken place. </p> </li>

</ul> </section>

</conbody><related-links>

<link href="GUID-0C3A4156-E5CF-55F9-91A0-A7961FDEE030.dita"><linktext>LCD Extension

Architecture</linktext></link>

<link href="GUID-8DF46A11-874A-52E5-9298-C083EA633BA0.dita"><linktext>Implementing

Dynamic DSA                 Allocation</linktext></link>

</related-links></concept>