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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<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>
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