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<concept id="GUID-984C2A0D-36BE-5A99-9D65-3F8791C669FF" xml:lang="en"><title>ASSP/Variant
Architecture</title><shortdesc>A base port must provide a software layer called the ASSP/Variant.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>The ASSP/Variant layer provides two main functions. First, it implements
a small number of hardware-specific functions that are used by the Kernel.
Second, it implements common peripheral control functions that other extensions
and device drivers can use. </p>
<p id="GUID-95C34114-F986-5428-9D40-5CF64429CDBD">  The most important of
these functions is interrupt dispatching. During initialisation the ASSP/Variant
must specify a dispatch function to be called for all hardware interrupts. </p>
<p>In general, the ASSP/Variant provides control functions for hardware which
is shared between multiple devices. For example it is often not possible to
do a read-modify-write on a GPIO port in order to change the state of an individual
output line. This may be either because an output port register is write-only
or because reading the port register reads the actual logic levels on the
pins, not the last value written to the register, and the pin level typically
lags the written value due to capacitive loading. In this case, the ASSP/Variant
could provide a function to set and clear individual port bits, keeping a
RAM copy of the last value written to the port register. </p>
<p>The simplest implementation is put all the code in a single DLL, called
the Variant DLL (<filepath>ecust.dll</filepath>). For hardware architectures
based on an ASSP, you can allow multiple types of phones that use the same
ASSP to share the common code. To do this, the common ASSP code is implemented
in a kernel extension, and the Variant DLL implements the code that is specific
to the phone type. </p>
<fig id="GUID-A42AFED6-372D-54A3-BC9D-FA99725464EF">
<image href="GUID-71271D1C-C385-5687-8A90-46E8B590BB1E_d0e365587_href.png" placement="inline"/>
</fig>
<p>In the Base Porting Guide, we refer to the ASSP layer and the Variant Layer,
where the ASSP layer contains the source code tailored to a range of different
microprocessors (e.g. ARM720/920/SA1/Xscale), and the Variant layer contains
the source code associated with off-chip hardware (same CPU, different peripherals). </p>
<p>For example, the standard Symbian port for the template reference board
is split into a core layer (in directory <filepath>...\template_assp\...</filepath>)
and code specific to the template board (in directory <filepath>...\template_variant\...</filepath>).
The <filepath>.mmp</filepath> file for the ASSP layer is <filepath>...\template_assp\katemplate.mmp</filepath>,
and the <filepath>.mmp</filepath> file for the Variant layer is <filepath>...\template_variant\vtemplate.mmp</filepath>. </p>
<section id="GUID-C05E021D-6DD6-5169-947B-192026A4364F"><title>The Asic class</title> <p>The
heart of the ASSP/Variant is the <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita"><apiname>Asic</apiname></xref> class, defined in <filepath>..\e32\include\kernel\arm\assp.h</filepath>.
This is a class that contains a number of pure virtual functions that must
be implemented. </p> <p>Where there is an ASSP/Variant split, the ASSP layer
should derive a concrete implementation from the <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita"><apiname>Asic</apiname></xref> class.
The most convenient way of implementing the Variant layer is to further derive
from this ASSP class. Only the Variant DLL is declared as ‘variant’ in the
ROM – the ASSP is declared as an extension. If there is no ASSP/Variant split,
then the Variant is simply a concrete implementation of the <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita"><apiname>Asic</apiname></xref> class. </p> <p>The
ASSP layer can, itself, define additional functions to be implemented in the
Variant layer. For example, the ASSP layer defines the pure virtual function <codeph>VideoRamSize()</codeph> which
the Variant layer provides to map the video frame buffer. </p> <p>The template
reference board port has the ASSP/Variant split. The ASSP layer is implemented
by the <codeph>TemplateAssp</codeph> class, and the Variant layer is implemented
by the <codeph>Template</codeph> class. </p> <p>For reference: the template
port ASSP layer implementation's <filepath>.mmp</filepath> file is at <filepath>...\template_assp\katemplate.mmp</filepath>,
and the Variant layer implementation's <filepath>.mmp</filepath> file is at <filepath>...\template_variant\vtemplate.mmp</filepath>. </p> <p>Note
that one of the source files that forms the ASSP layer must have the <codeph>DECLARE_STANDARD_ASSP()</codeph> declaration.
See <filepath>...\template_assp\assp.cpp</filepath>. </p> </section>
</conbody><related-links>
<link href="GUID-E0DCBDCF-C056-53E5-A375-778327F848E4.dita"><linktext>Asic Class
                Tutorial</linktext></link>
<link href="GUID-B498EDA0-677E-5521-9E4F-24D7C2048F2E.dita"><linktext>Implementing
the ASSP                 Register</linktext></link>
<link href="GUID-5194A7B6-471B-5BCF-8569-16A3BA59000A.dita"><linktext>Using the
ASSP Register</linktext></link>
<link href="GUID-77DF7A6B-F01D-5B9F-9C7A-662A04ED8BE7.dita"><linktext>ASSP Kernel
Extension                 Overview</linktext></link>
<link href="GUID-89291394-ABDF-5895-9E09-0D80D7A9F3EC.dita"><linktext>Integrated
Interchip Sound</linktext></link>
</related-links></concept>