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<concept id="GUID-D34DB4A1-1B17-5FAF-A48B-E06D247B0A83" xml:lang="en"><title>Keyboard
Mapping DLL Tutorial</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>A keyboard mapping DLL provides a set of lookup tables that the generic <filepath>ektran.dll</filepath> uses
to convert scancodes to keycodes. A keyboard mapping DLL is implemented in
a base port. </p>
<p>The basic purpose of the tables is to provide a mapping from scancodes
to keycodes, so that, given a scancode, the corresponding keycode can be found.
The tables are organised so that there is, in effect, one set of lookup tables
for each likely combination of modifier key states. <filepath>ektran.dll</filepath> compares
the modifier keys that have been pressed with the stored modifier key state
combinations to decide which set of lookup tables to use. </p>
<p>An outline set of tables is provided in the template port. The ports for
the H4 reference board provide useful examples of how the tables can be constructed. </p>
<p>The following list outlines the structure of the tables. </p>
<ol id="GUID-54817A2B-F65D-5BDF-BFCF-3E68A582C91A">
<li id="GUID-0C32BD32-0EFD-5622-9C66-2610A3D7F660"><p>The tables are organised
in a hierarchical structure. The start of this hierarchy is the root table,
defined by a <xref href="GUID-F7DFE751-C534-36A8-9B57-9C8417B1BE06.dita"><apiname>SConvTable</apiname></xref> struct. This contains: </p> <ul>
<li id="GUID-98675F02-D273-5C0D-8AF1-A9F93F8A5AC2"><p>an array of pointers
to nodes, where each node is defined by the <xref href="GUID-3D2F56DB-DD36-3787-8653-C5AC114D69A1.dita"><apiname>SConvTableNode</apiname></xref> struct.
Each node corresponds to a specific combination of modifier key states. </p> </li>
<li id="GUID-8321989A-20FE-58C3-90D0-2D3BE29E11F6"><p>a field containing the
total number of such nodes. </p> </li>
</ul> <fig id="GUID-A8C68654-2D56-501F-8D45-C0F75E63B630">
<image href="GUID-FB69F45C-2256-5F2D-8D2C-98C93B865962_d0e388142_href.png" placement="inline"/>
</fig> </li>
<li id="GUID-C232C328-190D-59F1-A1CB-BC9D736367B0"><p>The combination of modifier
key states that each node represents is encapsulated by a <xref href="GUID-7D0DE872-AC17-3045-9F97-E25A13B5CFB0.dita"><apiname>TMaskedModifiers</apiname></xref> object.
One of these objects is embedded within each node. </p> <p>A <xref href="GUID-7D0DE872-AC17-3045-9F97-E25A13B5CFB0.dita"><apiname>TMaskedModifiers</apiname></xref> object
consists of a mask, and a value for comparison. For example, if an instance
is set to the following: </p> <codeblock id="GUID-E53A8286-C304-50BD-9DB5-81777B48A2E3" xml:space="preserve">iMask = EModifierShift | EModifierCtrl | EModifierFunc
iValue = EModifierShift | EModifierFunc</codeblock> <p>then a match occurs
only for the following combination of modifier key states: </p> <p> <codeph>ctrl</codeph> + <codeph>shift</codeph> + <i>not</i> <codeph>Fn</codeph>  </p> <p>i.e. a match occurs only if <codeph>ctrl</codeph>  <i>and</i> <codeph>shift</codeph> are
pressed, and only if <codeph>Fn</codeph> is <i>not</i> pressed. Other modifier
keys are ignored, i.e. it does not matter whether or not they are pressed. </p> <p>In
C++ code, this is expressed as: </p> <codeblock id="GUID-E84542A2-932F-50C6-90B6-2AFC72CBE75F" xml:space="preserve">inline TBool MatchesMaskedValue(TInt aModifiers,const TMaskedModifiers &amp;aMaskedModifiers)
    {
    return (TBool)((aModifiers &amp; aMaskedModifiers.iMask) == aMaskedModifiers.iValue);
    }</codeblock> <p>where <codeph>aModifiers</codeph> contains the modifier
key combination to be tested. </p> </li>
<li id="GUID-C147C929-63EE-593B-8CB7-689E5E6E60C2"><p>In principle, each node
represents scancode-to-keycode mappings by associating one or more <i>pairs</i> (or
range) of scancodes with corresponding blocks of keycodes. Each pair represents
an inclusive and contiguous range of scancodes. </p> <p>Each pair (or range)
of scancodes may be "discontiguous" from the next. </p> <p>The association
is made through a table defined by the <xref href="GUID-35A21F70-F080-364D-8655-5E1781B378EB.dita"><apiname>SConvSubTable</apiname></xref> struct.
This has: </p> <ul>
<li id="GUID-9A023CDD-FADF-5641-8DD8-30C11F73E8BE"><p>a <xref href="GUID-DB86A3E5-D118-3A1D-8A76-BEC6111993E8.dita"><apiname>SScanCodeBlockList</apiname></xref> object
that contains pointers to a number of <xref href="GUID-F18D6A71-122E-3202-927B-25DCEF1576A4.dita"><apiname>SScanCodeBlock</apiname></xref> objects,
each of which contains the start and end values defining a range of scancodes. </p> </li>
<li id="GUID-AC4820E0-F3D9-547A-9437-964D5A7FE540"><p>a pointer to a table
containing the target keycodes. The target keycodes are arranged so that successive
scancode pairs are associated with successive blocks of keycodes as the following
diagram shows. </p> </li>
</ul> <fig id="GUID-4B2FBB49-6CBD-5030-82D0-9B4DDF2D3DBF">
<image href="GUID-DFADEB44-4D57-564F-ABDF-A3CCD38ACABC_d0e388253_href.png" placement="inline"/>
</fig> <p>This means that successive scancodes, for example, from "A1" through
to "B1" are represented by the successive keycodes "keycode for A1" through
to "keycode for B1"; scancode "A2" is represented by "keycode for A2", which
follows "keycode for B1" in the keycode table. </p> </li>
<li id="GUID-68C8A342-A3D2-5975-82F1-F635E366F741"><p>To allow for possible
reuse of keycode tables, a node can point to more than one <xref href="GUID-35A21F70-F080-364D-8655-5E1781B378EB.dita"><apiname>SConvSubTable</apiname></xref>.
The following diagram shows an example of this: </p> <fig id="GUID-3F5514B5-86E6-52BE-A4C2-38882A1CEACA">
<image href="GUID-5FDAF564-6BE1-544A-B5C0-E0D6E25D82E7_d0e388270_href.png" placement="inline"/>
</fig> </li>
<li id="GUID-C6001149-460A-57D4-A9FE-BCB050B49791"><p>If no keycode can be
found that matches the scancode, for a given modifier combination, then the
algorithm returns the <xref href="GUID-76B2E62E-EC09-3CA9-8B2D-EBAC6BF1FFDB.dita"><apiname>EKeyNull</apiname></xref> keycode. </p> </li>
</ol>
<section id="GUID-A7823728-26DD-4C2F-A97F-91CC4D58B404"><title>See also</title> <p> <xref href="GUID-EB76FAF8-CD4B-5CB6-9F23-C852ED91866F.dita">Concepts</xref>  </p> </section>
</conbody></concept>