1 <?xml version="1.0" encoding="utf-8"?>

     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

     3 <!-- This component and the accompanying materials are made available under the terms of the License 

     4 "Eclipse Public License v1.0" which accompanies this distribution, 

     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

     6 <!-- Initial Contributors:

     7     Nokia Corporation - initial contribution.

     8 Contributors: 

     9 -->

    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-6AC01B10-92C1-4E56-813B-6853DFCF3386-GENID-1-2-1-9-1-6-1-8-1-7-1-5-1" xml:lang="en"><title>DMA Requests</title><shortdesc>Describes how device drivers use DMA requests to initiate

    13 a DMA transfer.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>DMA transfer requests are the way in which a device driver sets

    15 up and initiates a DMA transfer. A transfer request internally comprises

    16 a linked list of DMA descriptor headers and is associated with a single

    17 DMA channel. A transfer request also stores an optional client-provided

    18 callback function, which can be invoked when the whole request completes,

    19 whether successfully or not. A DMA request can be in any of the four

    20 states: Not configured, Idle, Being transferred, and Pending. However,

    21 these states are not used by the driver. </p>

    22 <p>A device driver creates a DMA request by specifying a DMA channel

    23 and an optional DMA callback function to be called after the request

    24 completion. A DMA request must be fragmented. </p>

    25 <p>The following shows the creation of a DMA request: </p>

    26 <codeblock id="GUID-B2753DE7-800E-57CC-B2B6-CA2548AC25C4-GENID-1-2-1-9-1-6-1-8-1-7-1-5-1-3-4" xml:space="preserve">TInt DExDriverUartTxDma::Init()

    27     {

    28     ...

    29     // A DMA request has to be created for any DMA transfer. This 

    30     // specifies the channel on which the DMA request shall be 

    31     // made, the service callback function to be called after the 

    32     // request completion (TxDmaService), and an object pointer that will be passed 

    33     // as an argument to DMA request service function (this).

    34     // A DMA request is a list of fragments small enough to be 

    35     // transferred in one go by the DMA Controller.

    36     //

    37     iTxDmaRequest = new DDmaRequest(*iTxDmaChannel, TxDmaService,    this);

    38     if(iTxDmaRequest == NULL)

    39         {

    40         return KErrNoMemory;

    41         }

    42     ...

    43     }</codeblock>

    44 </conbody></concept>