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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-812DEBEB-84D0-5BD4-A5BB-5AF6B8384CCF" xml:lang="en"><title>Entry
Point Implementation</title><shortdesc>Describes how to implement the entry point function.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>The DMA Framework implements its entry point function in the platform-specific
layer. </p>
<p>The entry point for a kernel extension is declared by a </p>
<codeblock id="GUID-92670D2D-AB81-5BEA-8008-5BA7B0D23EF6" xml:space="preserve">DECLARE_STANDARD_EXTENSION()</codeblock>
<p>statement, followed by the block of code that runs on entry to the DLL.
The following code is typical for a port of the DMA Framework , and is taken
from the port for the template reference platform: </p>
<codeblock id="GUID-ED426309-D8FC-512C-B320-C29B37C74140" xml:space="preserve">DECLARE_STANDARD_EXTENSION()
//
// Creates and initializes a new DMA controller object on the kernel heap.
//
    {
    __KTRACE_OPT2(KBOOT, KDMA, Kern::Printf("Starting DMA Extension"));

    return Controller.Create();
    }
</codeblock>
<p>where <codeph>Controller</codeph> is declared as writable static data: </p>
<codeblock id="GUID-DA2508CF-BB22-5A48-B549-63D973E9EDB7" xml:space="preserve">static TTemplateDmac Controller;</codeblock>
<p>Create() is a second-phase constructor defined in, and implemented by,
the concrete class derived from <xref href="GUID-25398075-927B-36E4-B953-16785EC4086C.dita"><apiname>TDmac</apiname></xref>. DMA channels are
attributes of this concrete class because only the platform specific layer
knows what kind of channel to use. This platform specific layer second phase
constructor must call the platform independent layer second phase constructor, <xref href="GUID-25398075-927B-36E4-B953-16785EC4086C.dita#GUID-25398075-927B-36E4-B953-16785EC4086C/GUID-9B0C8C35-F149-3358-90B8-B4670CFE888F"><apiname>TDmac::Create()</apiname></xref>,
before doing anything else. </p>
<p> <xref href="GUID-25398075-927B-36E4-B953-16785EC4086C.dita#GUID-25398075-927B-36E4-B953-16785EC4086C/GUID-9B0C8C35-F149-3358-90B8-B4670CFE888F"><apiname>TDmac::Create()</apiname></xref> allocates the arrays containing the
descriptors and descriptor headers using the information passed to it by the
platform specific layer in the <xref href="GUID-4057074E-2543-3F01-B24A-7FF8A19F79AF.dita"><apiname>SCreateInfo</apiname></xref> struct. This
includes information such as the number of descriptors to be allocated, whether
hardware descriptors are supported and their size etc. </p>
<p>Note that if hardware-specific descriptors are used, they are allocated
in a hardware chunk. If pseudo-descriptors are used, they are allocated on
the kernel heap. </p>
</conbody></concept>