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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_d0e1517_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>
</related-links></concept>