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<concept id="GUID-C661B40F-1439-587F-9E8E-DB2DFC79C040" xml:lang="en"><title>HAL Groups</title><shortdesc>Description of HAL groups to add new attributes.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>You can extend <xref href="GUID-9AE254D4-AA60-579E-8D9D-F2797106A413.dita#GUID-9AE254D4-AA60-579E-8D9D-F2797106A413/GUID-366CC4B8-C6BD-5DCC-B55D-6D87CD5C8E64">HAL
groups</xref> to add new attributes and new types of hardware. </p>
<section id="GUID-7ACAB5F0-08A8-4D53-9F47-9E77642F7337"><title>Extending an existing hardware type</title> <p>Each HAL group
has an associated set of function numbers. For example, the enumerators of <codeph>TDisplayHalFunction</codeph>,
in <filepath>u32std.h</filepath> define the functions associated with the
HAL group <codeph>EHalGroupDisplay</codeph>. </p> <p>In this specific case,
new state can be represented by a new function number, and by changing the <xref href="GUID-9AE254D4-AA60-579E-8D9D-F2797106A413.dita#GUID-9AE254D4-AA60-579E-8D9D-F2797106A413/GUID-1B59A40C-D023-5555-8E5E-DF18D653D321">HAL
handler implementation</xref> to deal with the new function number. </p> <p>It
is important to note that any new function numbers should not follow consecutively
from those defined by Symbian. Instead, choose high values so that they are
guaranteed not to clash with any future Symbian extensions. Symbian will always
use new values that follow consecutively from previous Symbian defined values. </p> </section>
<section id="GUID-A819D9EA-A16F-4806-B8E8-C7ED008C6D31"><title>New hardware type</title> <p>Although up to 32 HAL groups
can be defined, Symbian OS does not use all 32. This leaves some values that
can be used for new hardware. </p> <p>In this case choose a HAL group number
at the high end of the range, so that it is guaranteed not to clash with any
future Symbian extensions. Symbian will always use new values that follow
consecutively from previous Symbian defined values. </p> </section>
</conbody></concept>