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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-58AA7257-0951-42AB-9B6E-AAF63343FEFA-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-5-1" xml:lang="en"><title>DMA Channel Operations</title><shortdesc>Describes how a device driver should open and close a DMA |
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13 channel.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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14 <section id="GUID-C4241738-D4C3-4171-87B2-5EDFFACE4002-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-5-1-3-1"><title>Open</title><p>To use a DMA channel it has to be opened. <xref href="GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37.dita#GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37/GUID-514BA285-3563-3C24-A067-F360098A6ADF"><apiname>TDmaChannel::Open()</apiname></xref> must be called to open the channel, and the required information |
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15 provided in a <xref href="GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37.dita#GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37/GUID-6B973278-8BE7-3CE5-97D8-60E8D3F4D473"><apiname>TDmaChannel::SCreateInfo</apiname></xref> structure. |
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16 The actual DMA channel selection is done by the hardware specific |
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17 layer. </p> <codeblock id="GUID-A1CA8DBA-1378-502B-8CC8-6D83F13DD151-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-5-1-3-1-3" xml:space="preserve">/** |
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18 Initializes the DMA for transmit. This function does all the |
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19 required generic initialization to use the DMA framework. This |
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20 function does not have any variant specific initialization. |
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21 |
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22 @return KErrNone on success, else standard error code on failure |
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23 */ |
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24 TInt DExDriverUartTxDma::Init() |
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25 { |
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26 ... |
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27 |
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28 // Initialize the channel information to select and configure the DMA |
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29 // channel |
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30 TDmaChannel::SCreateInfo info; |
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31 info.iCookie = (TUint); |
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32 info.iDesCount = 1; // For single buffered transfers |
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33 info.iDfcPriority = 4; // Set the priority of this DFC for DMA |
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34 info.iDfcQ = iUartComm->DfcQ(); // DFCQ onto which this request |
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35 // has to be queued |
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36 |
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37 // DMA channel has to be opened before doing any operations on |
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38 // the channel. TDmaChannel::Open() opens the DMA channel as |
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39 // set by info passed and selected by the hardware-specific layer. |
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40 |
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41 r = TDmaChannel::Open(info, iTxDmaChannel); |
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42 if (r!=KErrNone) |
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43 { |
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44 return r; |
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45 } |
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46 ... |
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47 }</codeblock> </section> |
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48 <section id="GUID-5E09A55C-A2B9-4E02-9BCF-F23558357B70-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-5-1-3-2"><title>Close</title> <p>A DMA channel has to be closed after completing all the DMA operations. |
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49 This releases the DMA channel for other resources and peripherals. |
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50 To close a previously opened channel, the channel should be idle, |
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51 with no pending requests. So, before closing, call <xref href="GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37.dita#GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37/GUID-0A98D2DC-2A61-3FBD-AB7A-623FE926A183"><apiname>TDmaChannel::CancelAll()</apiname></xref>, which cancels the current request and any pending DMA requests. |
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52 This should then be followed by closing the channel using <xref href="GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37.dita#GUID-83882548-FAC5-3EFF-92ED-14D1D9A85D37/GUID-8204AFBD-2A60-372E-B626-35BD19851FF7"><apiname>TDmaChannel::Close()</apiname></xref>. </p> <codeblock id="GUID-4BA5CDD2-6BD3-5179-89B8-7337ED5809AA-GENID-1-2-1-10-1-5-1-5-1-1-7-1-9-1-5-1-3-2-3" xml:space="preserve">/** |
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53 Destructor. Deinitializes the member variables, cancels any |
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54 requests, closes the channel, deletes the DMA requests, frees the |
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55 hardware chunks allocated. |
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56 */ |
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57 |
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58 DExDriverUartTxDma::~DExDriverUarttxDma() |
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59 { |
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60 ... |
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61 // if DMA channel is existing, cancel all requests on it. |
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62 // |
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63 if (iTxDmaChannel) |
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64 { |
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65 // TDmaChannel::CancelAll() cancels the current request and |
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66 // any pending requests on the DMA channel |
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67 // |
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68 iTxDmaChannel->CancelAll(); |
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69 } |
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70 ... |
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71 |
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72 if(iTxDmaChannel) |
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73 { |
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74 // Close the DMA channel. TDmaChannel::Close() closes a |
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75 // previously opened channel. All the requests on this |
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76 // channel should have been cancelled prior to this, i.e. |
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77 // TDmaChannel::CancelAll() should have been called before |
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78 // this call. |
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79 // |
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80 iTxDmaChannel->Close(); |
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81 } |
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82 ... |
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83 }</codeblock> <p>To stop DMA without closing the channel, simply |
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84 cancel the request. </p></section> |
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85 </conbody><related-links> |
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86 <link href="GUID-C649DB97-F138-4C90-B177-16590F2E3F19-GENID-1-2-1-9-1-6-1-8-1-7-1-3-1.dita"><linktext>DMA |
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87 Channels</linktext></link> |
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88 </related-links></concept> |