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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">

</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>