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<concept id="GUID-F9558573-7C79-57C5-809A-9257BF84758A" xml:lang="en"><title>Architecture</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>This topic describes the architecture of keyboard drivers and related components
on Symbian platform. </p>
<p>There are five components involved in this process: </p>
<ul>
<li id="GUID-0C41EB6F-3AD4-5B89-863E-EA7E108C73C9"><p> <i> The keyboard hardware</i>. </p> </li>
<li id="GUID-F965ADEC-3367-509F-A1B2-C5A5613410F6"><p> <i> A keyboard device
driver</i>. </p> <p>The keyboard driver is implemented as a standard kernel
extension, and is loaded by the kernel at boot time. A keyboard driver must
be implemented in the base port, and has no platform independent parts. </p> </li>
<li id="GUID-CBF257DE-AB08-5B96-AC15-E9981EA3484D"><p> <i>A keyboard mapping
DLL</i>. </p> <p>A keyboard mapping DLL provides a set of lookup tables that
map codes for the hardware keys to standard logical keycodes that user-side
applications can process. </p> <p>The DLL is platform specific. It must be
implemented in the base port, and has no platform independent parts. It is
usually called <filepath>ekdata.dll</filepath>. </p> </li>
<li id="GUID-52F97FEE-9B5B-5046-BF0C-EF1E4E2EB2BC"><p> <i>The Window Server</i>. </p> <p>The
Window Server is a system server that manages access to the screen and input
devices for user-side programs. </p> </li>
<li id="GUID-216989CD-45CE-5F59-831B-03B49BE4E73D"><p> <i>The keyboard translator</i>. </p> <p>The
keyboard translator DLL translates scancodes into keycodes using the data
in the platform specific keyboard mapping DLL. </p> <p>It is part of Symbian
platform generic code and is built as part of the Text Window Server component. </p> </li>
</ul>
<p>The following diagram shows how these components fit together and gives
an overview of the data flow. </p>
<fig id="GUID-D05ABF3B-3A1D-5F02-B268-FC1A992EE4DB">
<image href="GUID-9CC514E9-85C2-5F4B-9F3B-F9FA1F4CB20A_d0e387531_href.png" placement="inline"/>
</fig>
<p>Depending on the keyboard hardware, key presses in the form of key-down
and key-up events are registered by the keyboard driver, either as a result
of hardware interrupts, or as a result of polling the hardware. The driver
assigns a standard scancode value to the key. This is one of the values defined
by the <xref href="GUID-4D92CE24-E651-3584-BDE0-F26046B4175B.dita"><apiname>TStdScanCode</apiname></xref> enum. The value is a representation
of the hardware key. </p>
<p>The driver creates <xref href="GUID-668CEA36-3933-3BBE-A980-CAB62617B4FD.dita"><apiname>TRawEvent</apiname></xref> objects, of type <xref href="GUID-668CEA36-3933-3BBE-A980-CAB62617B4FD.dita#GUID-668CEA36-3933-3BBE-A980-CAB62617B4FD/GUID-ED6DCE25-227F-3353-8BE8-1C8F735198A8"><apiname>TRawEvent::EKeyUp</apiname></xref> and <xref href="GUID-9398BE98-2C09-333C-97D3-EFAD86400F8F.dita"><apiname>TRawEvent:EKeyDown</apiname></xref>, and includes the standard scancode value and modifiers as part of the object.
These objects are added to the kernel's event queue, using the <xref href="GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D.dita#GUID-C6946ECB-775F-3EC2-A56F-78F25B9FBE3D/GUID-81C82FED-0E26-351A-901E-806843C808FE"><apiname>Kern::AddEvent()</apiname></xref> function. </p>
<p>The Window Server captures these events and passes the scancode value to <filepath>ektran.dll</filepath>,
which has the responsibility for translating this value into a keycode value.
A keycode value is a logical representation of the key; it is this logical
representation that has meaning for the generic Symbian platform. The logical
keycode is one of the values defined by the <xref href="GUID-B67B6ED5-6C8F-3B36-934C-B47A109A515F.dita"><apiname>TKeyCode</apiname></xref> enum.
Also, <filepath>ektran.dll</filepath> tells the Window Server whether a capture
key has been pressed - this is explained in <xref href="GUID-110DB7EF-5E85-5BC4-9BBB-9A37B2D0C3A6.dita">Dynamic
Behaviour</xref>. </p>
<p> <filepath>ekdata.dll</filepath> encapsulates a set of tables that are
used to map hardware scancodes to logical keycode values. This is platform
specific code, and is used by the generic <filepath>ektran.dll</filepath> when
doing the translation. </p>
</conbody></concept>