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1 <?xml version="1.0" encoding="utf-8"?> |
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2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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3 <!-- This component and the accompanying materials are made available under the terms of the License |
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4 "Eclipse Public License v1.0" which accompanies this distribution, |
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5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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6 <!-- Initial Contributors: |
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7 Nokia Corporation - initial contribution. |
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8 Contributors: |
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9 --> |
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10 <!DOCTYPE concept |
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11 PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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12 <concept id="GUID-6AC01B10-92C1-4E56-813B-6853DFCF3386-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-4-1" xml:lang="en"><title>DMA Requests</title><shortdesc>Describes how device drivers use DMA requests to initiate |
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13 a DMA transfer.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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14 <p>DMA transfer requests are the way in which a device driver sets |
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15 up and initiates a DMA transfer. A transfer request internally comprises |
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16 a linked list of DMA descriptor headers and is associated with a single |
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17 DMA channel. A transfer request also stores an optional client-provided |
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18 callback function, which can be invoked when the whole request completes, |
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19 whether successfully or not. A DMA request can be in any of the four |
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20 states: Not configured, Idle, Being transferred, and Pending. However, |
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21 these states are not used by the driver. </p> |
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22 <p>A device driver creates a DMA request by specifying a DMA channel |
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23 and an optional DMA callback function to be called after the request |
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24 completion. A DMA request must be fragmented. </p> |
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25 <p>The following shows the creation of a DMA request: </p> |
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26 <codeblock id="GUID-B2753DE7-800E-57CC-B2B6-CA2548AC25C4-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-4-1-3-4" xml:space="preserve">TInt DExDriverUartTxDma::Init() |
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27 { |
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28 ... |
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29 // A DMA request has to be created for any DMA transfer. This |
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30 // specifies the channel on which the DMA request shall be |
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31 // made, the service callback function to be called after the |
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32 // request completion (TxDmaService), and an object pointer that will be passed |
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33 // as an argument to DMA request service function (this). |
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34 // A DMA request is a list of fragments small enough to be |
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35 // transferred in one go by the DMA Controller. |
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36 // |
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37 iTxDmaRequest = new DDmaRequest(*iTxDmaChannel, TxDmaService, this); |
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38 if(iTxDmaRequest == NULL) |
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39 { |
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40 return KErrNoMemory; |
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41 } |
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42 ... |
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43 }</codeblock> |
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44 </conbody></concept> |