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    10 <!DOCTYPE concept

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    12 <concept id="GUID-4AEF7595-17C0-513E-9568-B212E6194388" xml:lang="en"><title>Record

    13 operation</title><shortdesc>Describes the operation of the Sound Driver for sound recording.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <section id="GUID-0722033C-4BC0-45D0-B980-C1FC680BBF70"><title>Client functions</title> <p>Many aspects regarding the way

    15 that the Sound Driver recording operates are similar to the way it handles

    16 playback. One difference is how the memory location in the <xref href="GUID-51514A4B-0220-557B-9F7A-FB110CEFEF10.dita">Shared

    17 Chunks</xref> for the transfer is determined. In play requests, the client

    18 specifies the source location in the chunk for the transfer having arranged

    19 for the data to be loaded there prior to the request. For record requests,

    20 the client just requests a buffers worth of record data and allows the driver

    21 to decide which buffer to use for the request. </p> <p>The driver commences

    22 recording when the client issues the first <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-D96D7433-6CB5-3368-8B51-C19731C474AF"><apiname>RSoundSc::RecordData()</apiname></xref> request.

    23 However, unlike playback operation, once recording has commenced, the driver

    24 continues to record data into its available record buffers until it is told

    25 to stop. To stop the driver capturing record data, the client must either

    26 issue <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-16C40CF6-C84D-3901-8527-EA66842E0AAC"><apiname>RSoundSc::Pause()</apiname></xref> to temporarily suspend recording, <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-4B53ED55-EC95-35B3-B9D6-A24EF70D81F9"><apiname>RSoundSc::CancelRecordData()</apiname></xref> to

    27 terminate record operation, or close the driver channel altogether. </p> <p>The

    28 client specifies the number and size of the record buffers available to the

    29 driver within the shared chunk by calling either <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-1978D84C-6E2A-39C0-AF5F-17C85E5B25B4"><apiname>RSoundSc::SetBufferChunkCreate()</apiname></xref>,

    30 to create a buffer, or <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-46096E39-A530-3644-91F0-0B97AC3C6580"><apiname>RSoundSc::SetBufferChunkOpen()</apiname></xref> to

    31 open an existing buffer. </p> <p>When the driver starts recording, all the

    32 buffers in the shared chunk are empty, and the driver can use all of these

    33 available buffers. They are filled one by one, and if the client is slow to

    34 request the recorded data, then once the driver has filled all of the available

    35 empty buffers, it is forced to discard the earliest one filled and re-use

    36 this to continue recording data. </p> <p>Each time the client requests a buffers

    37 worth of recorded data with <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-D96D7433-6CB5-3368-8B51-C19731C474AF"><apiname>RSoundSc::RecordData()</apiname></xref>, it

    38 is given the earliest one filled. This buffer is now said to be in-use and

    39 unavailable to the driver for capturing. This buffer remains in-use until

    40 it is freed by the client with a call of <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-26F7C97B-D06A-32BE-90B3-2E6918BF3F4D"><apiname>RSoundSc::ReleaseBuffer()</apiname></xref>. </p> <p>When

    41 buffers are in use by the client the number of buffers available to the driver

    42 for capture is reduced. If the client is slow to release buffers and the number

    43 of available buffers falls to two then further <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-D96D7433-6CB5-3368-8B51-C19731C474AF"><apiname>RSoundSc::RecordData()</apiname></xref> requests

    44 fail with <codeph>KErrInUse</codeph> until the client has freed some buffers.

    45 The driver always needs a working set of at least two buffers in order to

    46 achieve uninterrupted data capture. The driver always has a current buffer

    47 which is actively being filled and another queued in advance. If the client

    48 fails to take buffers at full speed then they are discarded by the driver. </p><p><note> The

    49 driver does not slow down if it runs out of empty buffers. </note></p> <p><b>Buffers</b> </p> <p>The driver maintains three buffer lists: </p> <ul>

    50 <li id="GUID-D0B884B5-3687-5CB9-B732-1B028F0008A8"><p>free list </p> </li>

    51 <li id="GUID-3A3FAAA7-72C2-5A35-9F4D-3824966D3D52"><p>completed list </p> </li>

    52 <li id="GUID-E571D299-99C5-51D1-832E-55A88533B365"><p>in-use list. </p> </li>

    53 </ul> <p>A record buffer can only exist in one of these lists at any time.

    54 The free list contains buffers that are empty and not in use by the client.

    55 Once a buffer has been filled with record data it is moved into the completed

    56 buffer list. Here the buffer remains until it is passed back to the client

    57 in response to a record request. When a client is using the buffer it is deemed

    58 as in-use and is moved to the <i>in-use</i> list. Each time the client successfully

    59 calls <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-26F7C97B-D06A-32BE-90B3-2E6918BF3F4D"><apiname>RSoundSc::ReleaseBuffer()</apiname></xref> to free up a buffer then

    60 the driver moves this from the in-use list to the free list. </p> <p>The driver

    61 also maintains two record buffers which are excluded from any of the three

    62 lists. </p> <ul>

    63 <li id="GUID-3EB509DB-F35F-51E7-AAD9-8A25EEDAE604"><p>the current buffer,

    64 the one actively being filled with record data </p> </li>

    65 <li id="GUID-E109F4E5-998D-5B19-AE82-A913BBF4CED3"><p>the next buffer which

    66 becomes the active buffer once the current buffer is filled </p> </li>

    67 </ul> <p>During recording there may be DMA requests pending for both the current

    68 buffer and the next buffers. </p> <fig id="GUID-FBF47E94-8334-55D3-9AC0-FDAF1F9960B1">

    69 <title>                 The record buffer cycle               </title>

    70 <desc><p>The numbers one to five show the buffer cycle under normal operation,

    71 while the letters A to C show error induced operation. </p> </desc>

    72 <image href="GUID-1A92047A-3C1D-5B4C-949B-98D770F5F530_d0e398658_href.png" placement="inline"/>

    73 </fig> <p>When recording commences, the driver removes two buffers from the

    74 free list making one the current buffer and the other the next buffer (4 and

    75 5). </p> <p>When the current buffer is set as filled, the LDD normally adds

    76 this to the completed list (1). If a record error has occurred while recording

    77 to this buffer and it is only partially filled, or even empty then the buffer

    78 is still added to the completed list, as the client needs to be informed of

    79 the error (1). The only exception is in handling record pause, where a record

    80 buffer ends up being completed with no error and with no data added. In this

    81 case the buffer is added straight into the free list (A). </p> <p>Having added

    82 the current buffer to one of these lists, the driver moves the next buffer

    83 to the current buffer (5) and then obtains a new next buffer (4). In normal

    84 operation this comes from the free list but if the client is slow, this list

    85 may be empty and the buffer is taken from the completed list (B). This is

    86 a buffer overflow situation which is reported to the client as a response

    87 to its next <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-D96D7433-6CB5-3368-8B51-C19731C474AF"><apiname>RSoundSc::RecordData()</apiname></xref> request as <codeph>KErrOverFlow</codeph>. </p> <p>Whenever

    88 a buffer is filled, the driver checks if there is a record request pending

    89 (1). Similarly, when the driver processes a new record request it checks if

    90 a filled buffer is already available. In either case, if a request can be

    91 completed to the client then the earliest buffer completed is returned. If

    92 this buffer was filled successfully then it added to the in-use list (2).

    93 However, if an error occurred whilst filling the buffer then it is returned

    94 straight to the free list instead (C). </p> <p>Each time the client successfully

    95 calls <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-26F7C97B-D06A-32BE-90B3-2E6918BF3F4D"><apiname>RSoundSc::ReleaseBuffer()</apiname></xref> to free up a buffer then

    96 the driver moves this from the in-use list to the free list (3). </p> </section>

    97 <section id="GUID-548515F6-403D-4C99-AAA3-027C7D303C73"><title>Audio recording</title> <p><b>RecordData()</b> </p> <p>If

    98 the driver is not already recording data then the first <xref href="GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3.dita#GUID-B0118EDD-2B08-353E-BE92-2DC75E5622B3/GUID-D96D7433-6CB5-3368-8B51-C19731C474AF"><apiname>RSoundSc::RecordData()</apiname></xref> request

    99 is handled in the context of the driver DFC thread, as access to the audio

   100 hardware is required to enable record operation. However, for efficiency,

   101 subsequent record requests from the client are handled entirely in the context

   102 of the calling thread, as access to the audio hardware is not required to

   103 handle the request. The driver only has to check whether there is a filled

   104 record buffer already available. If there is then the driver completes the

   105 request straight away. If not, the driver saves the details of the request

   106 until a filled buffer does become available. </p> <p>Returning to the case

   107 of a record request where the driver is not already in the process of recording

   108 data, the LDD first checks whether the client has specified or supplied a

   109 shared chunk to the driver channel and has set the audio configuration and

   110 record level. If the buffer configuration has not been specified then the

   111 driver cannot proceed and returns <codeph>KErrNotReady</codeph>. If the audio

   112 configuration or record level has not been specified then the LDD applies

   113 default settings to the audio hardware device for each instead by calling

   114 the functions <xref href="GUID-E1C67F8D-1A83-36B3-A451-22F496A659C6.dita#GUID-E1C67F8D-1A83-36B3-A451-22F496A659C6/GUID-23CEDA72-E161-30C4-B8D7-DBDCBC5B9C63"><apiname>DSoundSc::SetConfig()</apiname></xref> and <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-D893A29B-1A4B-35AF-876B-84D74B7E783C"><apiname>DSoundScPdd::SetVolume()</apiname></xref> on

   115 the PDD. </p> <p><b>StartTransfer()</b> </p> <p>Depending

   116 on the mapping attributes of the shared chunk, the LDD may now need to purge

   117 the region of the record chunk concerned. Next the LDD calls <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-54D3CC19-0C00-3FFA-BD1A-62618D36EB20"><apiname>DSoundScPdd::StartTransfer()</apiname></xref> on

   118 the PDD to allow it to prepare the audio hardware device for record data transfer. </p> <p><b>TransferData()</b> </p> <p>The LDD may need to break down the record buffer

   119 into memory fragments. These specify a physically contiguous region and are

   120 manageable by the PDD as a single transfer. The LDD queues as many transfer

   121 fragments of the current buffer on the PDD as it can accept with a call to <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref> for

   122 each fragment. If all fragments from the current buffer are accepted by the

   123 PDD then the LDD tries to queue fragments from the next buffer. As with playback,

   124 to support uninterrupted transfer of audio data the PDD must be able to accept

   125 multiple fragments simultaneously. As long as the LDD has transfer fragments

   126 still to queue, it continues to call <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref> until

   127 the PDD signals that it has temporarily reached its capacity by returning <codeph>KErrNotReady</codeph>. </p> <p><b>RecordCallBack()</b> </p> <p>Each time the PDD completes the transfer

   128 of a fragment from a record buffer, it must signal this event back to the

   129 LDD by calling the function <xref href="GUID-5807543D-A30F-3EB9-8F28-91A623B0D484.dita#GUID-5807543D-A30F-3EB9-8F28-91A623B0D484/GUID-9112E399-DC3C-334F-BE16-B5F42216F903"><apiname>DSoundScLdd::RecordCallBack()</apiname></xref>.

   130 This must always be called in the context of the driver DFC thread. In executing <xref href="GUID-5807543D-A30F-3EB9-8F28-91A623B0D484.dita#GUID-5807543D-A30F-3EB9-8F28-91A623B0D484/GUID-434E378F-0C48-39D9-8FB8-9831A1F704C0"><apiname>DSoundScLdd::RecordCallback()</apiname></xref>,

   131 the LDD checks whether the entire transfer for the current buffer is now complete.

   132 If so, depending on the mapping attributes of the shared chunk, the LDD may

   133 need to purge the region of the record client. The LDD attempts to queue further

   134 fragments on the PDD, by calling <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref>,

   135 which should now have the capability to accept more transfers. So, the PDD

   136 should be written to handle calls to <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref> within

   137 its call back to <xref href="GUID-5807543D-A30F-3EB9-8F28-91A623B0D484.dita#GUID-5807543D-A30F-3EB9-8F28-91A623B0D484/GUID-434E378F-0C48-39D9-8FB8-9831A1F704C0"><apiname>DSoundScLdd::RecordCallback()</apiname></xref>. </p> </section>

   138 <section id="GUID-7B5CF9A4-8527-4C76-96CD-C03F861AF3BF"><title>Pause and resume audio recording</title> <p>The client can

   139 temporarily halt the progress of audio record at any time by issuing <xref href="GUID-5807543D-A30F-3EB9-8F28-91A623B0D484.dita#GUID-5807543D-A30F-3EB9-8F28-91A623B0D484/GUID-D912620F-9C51-3AFC-8A59-31AF9455AC4A"><apiname>DSoundScLdd::Pause()</apiname></xref>.

   140 To configure the audio hardware device to halt recording, the LDD calls <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-0608766F-2645-3E28-B804-BD4B953DB5FF"><apiname>DSoundScPdd::PauseTransfer()</apiname></xref> on

   141 the PDD. This time, any active transfer should be aborted by the PDD. If a

   142 recording is halted the PDD must signal this event with a single call of the

   143 LDD function <xref href="GUID-3731902C-9C34-3FAE-8F82-9F9493C2C2E7.dita#GUID-3731902C-9C34-3FAE-8F82-9F9493C2C2E7/GUID-73F74080-6219-3D9A-BA56-735A17A9ABA0"><apiname>DSOundScLdd::RecordCallback()</apiname></xref>, which reports

   144 back any partial data already received. In this case, if transfer is resumed

   145 later, the LDD issues a new <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref> request

   146 to commence data transfer after calling <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-C692BF61-FA3D-3B85-BCC6-1248C9C7D9BF"><apiname>DSoundScPdd::ResumeTransfer()</apiname></xref>.

   147 As access to the hardware is required in both cases, pause and resume are

   148 handled in the context of the driver DFC thread. </p> </section>

   149 <section id="GUID-BA951968-290F-4DA5-842A-2004664B1139"><title>Error handling during recording</title> <p>If the PDD reports

   150 an error when setting up the audio hardware device for recording then the

   151 LDD immediately completes the first record request back to the client returning

   152 the error value as the result. It will not restart record data transfer unless

   153 it receives a further record request from the client. </p> <p>If the PDD reports

   154 an error when commencing the transfer of a record fragment or as the result

   155 of the transfer of a record fragment, then the LDD ceases transfer to that

   156 record buffer and instead reports the error back to the client. The error

   157 is returned in response to the record request which corresponds with that

   158 buffer. </p> <p>Unexpected errors from the PDD are returned to the LDD via

   159 the functions <xref href="GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424.dita#GUID-61CC68CB-A01D-3CA0-93D9-F3717ABD6424/GUID-8C79D09B-317A-3D8E-B9C2-474812F17529"><apiname>DSoundScPdd::TransferData()</apiname></xref> and <xref href="GUID-5807543D-A30F-3EB9-8F28-91A623B0D484.dita#GUID-5807543D-A30F-3EB9-8F28-91A623B0D484/GUID-434E378F-0C48-39D9-8FB8-9831A1F704C0"><apiname>DSoundScLdd::RecordCallback()</apiname></xref>. </p> <p>The

   160 LDD does not try to cancel the transfer of other fragments for the same buffer

   161 that are already queued on the PDD, but it ignores their outcome. However,

   162 the LDD does try to carry on with the transfer to other available record buffers. </p> </section>

   163 </conbody></concept>