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<concept id="GUID-EBF025DB-1552-5E99-8C07-09932DB60552" xml:lang="en"><title>Physical

Channel Implementation</title><shortdesc>A media driver must implement a physical channel class derived

from the <codeph>DMediaDriver</codeph> base class. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p/>

<p>This includes those drivers associated with fixed media, such as the internal

drive, or removable media, such as a PC Card or MultiMediaCard. </p>

<p> <codeph>DMediaDriver</codeph> is an abstract class that has virtual functions

that must be implemented by your derived class. The following class definition

is typical: </p>

<codeblock id="GUID-B39837DA-6037-58D2-A1BE-3E7F1E218F7B" xml:space="preserve">class DMyMediaDriver : public DMediaDriver

    {

public:

    DMyMediaDriver (TInt aMediaId);

    ~DMmcMediaDriver ();

public:    

    virtual void Close();

public:    

    virtual void Disconnect(DLocalDrive* aLocalDrive, TThreadMessage*);

    virtual TInt Request(TLocDrvRequest& aRequest);

    virtual TInt PartitionInfo(TPartitionInfo& anInfo);

    virtual void NotifyPowerDown();

    virtual void NotifyEmergencyPowerDown();

public:

    TInt DoCreate(TInt aMediaId);

    };

      </codeblock>

<p>All the functions except the constructor and <codeph>DoCreate()</codeph> either

implement or re-implement virtual functions defined by <codeph>DMediaDriver</codeph>. </p>

<p>The framework does not require the <codeph>DoCreate()</codeph> function,

but it is useful to implement such a function to act as a second-phase constructor

in the creation of the media driver. In the example code fragments, we call <codeph>DoCreate()</codeph> from

the <xref href="GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930.dita#GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930/GUID-32B157E9-0F71-5C1B-A0FA-08D5B1ACA700">PDD

factory object's Create()</xref> function that is responsible for creating

the media driver. </p>

<p>There is, of course, nothing to stop you from adding your own functions

and data members, if this is appropriate for your implementation. In addition,

your are also free to add other classes, functions and enums to your media

driver implementation. </p>

<ul>

<li id="GUID-E17276B8-4595-5A45-89B0-D053A659A17E"><p> <xref href="GUID-EBF025DB-1552-5E99-8C07-09932DB60552.dita#GUID-EBF025DB-1552-5E99-8C07-09932DB60552/GUID-FE5BB479-7AC4-5DB8-87A3-55E855E1A176">Constructor</xref> </p> </li>

<li id="GUID-927ED2FA-9A58-5C99-85B6-44BAD9F2F47A"><p> <xref href="GUID-EBF025DB-1552-5E99-8C07-09932DB60552.dita#GUID-EBF025DB-1552-5E99-8C07-09932DB60552/GUID-D308D7F7-25B9-5A3A-BC19-A01C5948B949">DoCreate() - second phase constructor</xref>  </p> </li>

<li id="GUID-380702AD-FBC8-584A-B875-B7C23AC841DE"><p> <xref href="GUID-EBF025DB-1552-5E99-8C07-09932DB60552.dita#GUID-EBF025DB-1552-5E99-8C07-09932DB60552/GUID-4ABC799E-33EE-5260-9CD0-71F0A5E7F980">PartitionInfo() - return the partition information</xref>  </p> </li>

<li id="GUID-D0EC11D5-CC9C-5A45-BF5B-06CDBEB8738B"><p> <xref href="GUID-EBF025DB-1552-5E99-8C07-09932DB60552.dita#GUID-EBF025DB-1552-5E99-8C07-09932DB60552/GUID-EC193360-31C2-5012-8ED2-19F1C48C8FC5">Request() - handling requests</xref>  </p> </li>

</ul>

<section id="GUID-FE5BB479-7AC4-5DB8-87A3-55E855E1A176"><title>Constructor</title> <p>The

media driver object is created by your PDD factory object's implementation

of the <xref href="GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930.dita#GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930/GUID-32B157E9-0F71-5C1B-A0FA-08D5B1ACA700">Create()</xref> function.

The following is the relevant line of code: </p> <codeblock id="GUID-012D3CB1-7C35-590E-AA5D-FBD0F21F957F" xml:space="preserve">...

//Create my DMediaDriver derived object

DMyMediaDriver* pD=new DMyMediaDriver (aMediaId);

...</codeblock> <p>Your constructor, prototyped as: </p> <codeblock id="GUID-66FD6B05-D32B-5CD6-A546-B1B8E7733EE5" xml:space="preserve">DMyMediaDriver (TInt aMediaId);</codeblock> <p>gives you the chance to do any initialisation that is safe, i.e. that

cannot fail. Typically, this is the kind of initialisation that does not need

to acquire resources. This is the first phase of the typical Symbian platform

two-phase construction process. </p> <codeblock id="GUID-A1C95B09-C03B-531A-9E38-0E77F9E574F5" xml:space="preserve">DMyMediaDriver::DMyMediaDriver (TInt aMediaId)

    :DMediaDriver(aMediaId)

    {

    //…do safe initialisation here

    }

        </codeblock> <p>As this code fragment shows, you need to call the

base class constructor first, forwarding the <codeph>TInt aMediaId</codeph> value.

You do not need to do anything else with this value. Note that this value

is the unique media ID used when the media driver was registered. </p> </section>

<section id="GUID-D308D7F7-25B9-5A3A-BC19-A01C5948B949"><title>DoCreate()

- second phase constructor</title> <p>The media driver object is created by

your PDD factory object's implementation of the <xref href="GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930.dita#GUID-A6D14A03-ADBF-570D-8AC7-E8BC2700F930/GUID-32B157E9-0F71-5C1B-A0FA-08D5B1ACA700">Create()</xref> function. The following is the relevant line of code, which is called after

successful creation of the media driver object: </p> <codeblock id="GUID-003B4A82-853B-5ABF-A33F-69ED7AC520F9" xml:space="preserve">...

// Call my media driver’s second-stage constructor

Tint r = KErrNoMemory;

    if(pD)

        {

        r = pD->DoCreate(aMediaId);

        }

...

        </codeblock> <p>This is a second-phase constructor that allows you

to do more complex initialisation, and initialisation that might fail. Typically,

this is initialisation that acquires resources (including memory). The outline

implementation of <codeph>DoCreate()</codeph> is: </p> <codeblock id="GUID-4380C850-B722-52E5-A849-602312C2441D" xml:space="preserve">TInt DMyMediaDriver::DoCreate(TInt aMediaId)

    {

    TInt r = KErrNone;

    //…do complex initialisation here

    return r;

    }

        </codeblock> <p>Depending on the complexity of your initialisation,

you can either do all your initialisation here, and complete immediately,

or you can do the initialisation as an asynchronous operation, in which case

initialisation will complete at some later time. </p> <p>If you do this <i>synchronously</i>,

then the return code should reflect the success or failure of the operation.

In practice, this will almost always be <codeph>KErrNone</codeph>. </p> <p>If

you do this <i>asynchronously</i>, then, on completion of the initialisation

processing, a call should be made to: <codeph>DMediaDriver::OpenMediaDriverComplete()</codeph> passing

either <codeph>KErrNone</codeph> or one of the other system-wide codes as

appropriate. </p> </section>

<section id="GUID-4ABC799E-33EE-5260-9CD0-71F0A5E7F980"><title>PartitionInfo()

- return the partition information</title> <p>Once the media driver has been

successfully created and initialised, and has informed the media driver subsystem

of this fact by a call to <codeph>DMediaDriver::OpenMediaDriverComplete()</codeph>,

then the subsystem makes a call to the media driver's <codeph>PartitionInfo()</codeph> function

to get partition information for the media device. </p> <p>The prototype function

is: </p> <codeblock id="GUID-C22CA159-CDD5-5900-B753-64E1A481B6F1" xml:space="preserve">TInt PartitionInfo(TPartitionInfo&amp; anInfo);</codeblock> <p>A <xref href="GUID-00D1DAB7-C23A-30F4-B5A3-B47EED5A5DD3.dita"><apiname>TPartitionInfo</apiname></xref> object is passed to the function, which the media driver must fill in. </p> <p>Decoding

of partition information may require media access, and as such may be a long

running activity. Support is provided that allows this to be done asynchronously.

You use the <i>return code</i> from <codeph>PartitionInfo()</codeph> to tell

the media driver subsystem which operational mode you are using: </p> <ul>

<li id="GUID-6A5496C7-3896-5EA4-AF92-72BFAEAEED55"><p>return <b>KErrNone</b>,

if the decoding operation is to be done <b>asynchronously</b>. Note that on

completion, the asynchronous operation must call <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-1E38DA87-4D5C-3D3C-8FE9-145E5877D02A"><apiname>DMediaDriver::PartitionInfoComplete()</apiname></xref>,

returning <codeph>KErrNone</codeph>, or one of the other system-wide error

codes, if appropriate. </p> </li>

<li id="GUID-4F34B295-062F-5FCB-809B-73F19E4DE1A2"><p>return a value <b>other

than KErrNone </b>, if the decoding operation has been done <b>synchronously</b>.

If the synchronous operation is successful, return <i>KErrCompletion</i>,

otherwise return one of the other system-wide error codes, but not KErrNone. </p> </li>

</ul> <p><b>Decoding

simple partitions</b> </p> <p>The following example shows the implementation

of a simple <codeph>PartitionInfo()</codeph> function. Such an implementation

would be provided for non-removable media, such as internal Flash memory,

where the layout is simple and known to the system. </p> <p>This implementation

reports a single partition with the size of the entire media. The partition

expects to be mounted with the FAT filesystem. </p> <p>Note that this operation

is done synchronously, and the function returns <codeph>KErrCompletion</codeph> to

indicate this. </p> <codeblock id="GUID-3D99CC4D-5996-502B-8A3F-6DE4675EAFE5" xml:space="preserve">TInt DMyMediaDriver::PartitionInfo(TPartitionInfo&amp; aInfo)

    {

    aInfo.iPartitionCount                = 1;

    aInfo.iEntry[0].iPartitionBaseAddr    = 0;

    aInfo.iEntry[0].iPartitionLen        = TotalSizeInBytes();

    aInfo.iEntry[0].iPartitionType        = KPartitionTypeFAT12;

    aInfo.iMediaSizeInBytes                = TotalSizeInBytes();

    return KErrCompletion;

    }

          </codeblock> <p><b>Decoding

FAT Partitions</b> </p> <p>More complex implementations of <codeph>PartitionInfo()</codeph> may

be required when handling removable media or more complex internal media where

the layout of the media is unknown to the system. </p> <p>This example shows

a typical implementation for a FAT based removable media device. Here, <codeph>PartitionInfo()</codeph> starts

the operation, which is done asynchronously by the <codeph>DoPartitionInfo()</codeph> function. </p> <p>Note

that <codeph>PartitionInfo()</codeph> returns <codeph>KErrNone</codeph>, which

tells the media driver subsystem that the operation will be done asynchronously. </p> <p>Note

also that on completion, <codeph>DoPartitionInfo()</codeph> calls <codeph>PartitionInfoComplete()</codeph> to

tell the media driver subsystem that the operation is complete. </p> <codeblock id="GUID-17F9AD37-7D5F-5F8F-960B-EF36FBE03A04" xml:space="preserve">TInt DMyMediaDriverFlash::PartitionInfo(TPartitionInfo&amp; aInfo)

    {

    iPartitionInfo = &anInfo                        // Store aInfo until needed

    TInt errCode = LaunchPartitionInfoRequest();    // Start the asynchronous request

    return(errCode);    // This needs to be KErrNone to indicate that the operation

                        // will be completed asynchronously (unless an error occurs launching

                        // the asynchronous request!)

    }

          </codeblock> <p>This is the function that runs asynchronously </p> <codeblock id="GUID-84368231-7B29-5EE9-A93B-851C7E5C0B62" xml:space="preserve">TInt DMyMediaDriver::DoPartitionInfo()

    {

    TInt partitionCount = iPartitionInfo->iPartitionCount = 0;

    // Read of the first sector successful so check for a Master Boot Record

    if (*(TUint16*)(&iIntBuf[KMBRSignatureOffset])!=0xAA55)

        {

        return(KErrCorrupt);

        }

    // Move the partition entries to a 4 byte boundary

    memcpy(&iIntBuf[0],&iIntBuf[KMBRFirstPartitionEntry],(sizeof(TMBRPartitionEntry)<<2)); 

    // Search for a x86 default boot partition - let this be the first

    TMBRPartitionEntry *pe=(TMBRPartitionEntry*)(&iIntBuf[0]);

    TInt i;

    TInt defaultPartitionNumber=-1;

    for (i=0;i<KMaxPartitionEntries;i++,pe++)

        {

        if (pe->IsDefaultBootPartition())

            {

            SetPartitionEntry(&iPartitionInfo->iEntry[0],pe->iFirstSector,pe->iNumSectors);

            iHiddenSectors=pe->iFirstSector;

            defaultPartitionNumber=i;

            partitionCount++;

            break;

            }

        }

    // Now add any other partitions

    pe=(TMBRPartitionEntry*)(&iIntBuf[0]);     // Reset it

    for (i=0;i<KMaxPartitionEntries;i++,pe++)

        {

        if (defaultPartitionNumber==i)

            {

            continue;    // Already sorted

            }

        if (pe->IsValidDosPartition())

            {

            SetPartitionEntry(&iPartitionInfo->iEntry[partitionCount],pe->iFirstSector,pe->iNumSectors);

            if (partitionCount==0)

            iHiddenSectors=pe->iFirstSector;

            partitionCount++;

            }

        }

    if (defaultPartitionNumber==(-1) && partitionCount==0)

        {

        // Assume it has no MBR, and the Boot Sector is in the 1st sector

        SetPartitionEntry(&iPartitionInfo->iEntry[0], 0, iMediaSize);

        iHiddenSectors=0;

        partitionCount=1;

        }

    iPartitionInfo->iPartitionCount=partitionCount;

    iPartitionInfo->iMediaSizeInBytes=TotalSizeInBytes();

    PartitionInfoComplete(err);

    return(KErrNone);

    }

          </codeblock> </section>

<section id="GUID-EC193360-31C2-5012-8ED2-19F1C48C8FC5"><title>Request() -

handling requests</title> <p>You handle requests by implementing your media

driver's <codeph>Request()</codeph> function. This is prototyped as: </p> <codeblock id="GUID-2DABBFE2-5F74-5DC4-B1A5-E50A41258E8A" xml:space="preserve">TInt Request(TLocDrvRequest&amp; aRequest)=0;</codeblock> <p>This

function is usually called in the context of the client thread that originally

initiated the I/O request to the file server, although you should never assume

so. Note that you may also see the originating thread referred to as <i>the

remote thread</i>. </p> <p>The request type, as identified by the request

ID, and the information associated with the request is accessed through the <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita"><apiname>TLocDrvRequest</apiname></xref> object,

which is passed to the <codeph>Request()</codeph> function. The information

supplied includes offsets, data lengths, the requesting thread etc, but clearly

depends on the request ID. You get the request ID by calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-615CA1FE-0FDA-39F4-875D-FBB7B6F6FAD8"><apiname>TLocDrvRequest::Id()</apiname></xref>,

and this will be one of the <xref href="GUID-720001A0-79E6-3E25-B5F0-4B39EAF95D12.dita#GUID-720001A0-79E6-3E25-B5F0-4B39EAF95D12/GUID-0559A1ED-05A1-386E-B728-0D500ED4E3EA"><apiname>DLocalDrive::TRequestId</apiname></xref> enum

values. </p> <p>Each request ID, as defined by <xref href="GUID-720001A0-79E6-3E25-B5F0-4B39EAF95D12.dita#GUID-720001A0-79E6-3E25-B5F0-4B39EAF95D12/GUID-0559A1ED-05A1-386E-B728-0D500ED4E3EA"><apiname>DLocalDrive::TRequestId</apiname></xref> has

a specific meaning. The information that is available also depends on the

request ID. </p> <p>Depending on the request ID, the operation can be done

synchronously or asynchronously. However, it is the responsibility of the

implementor of the media driver to handle the incoming requests and to handle

them as appropriate to the specific media, i.e. synchronously or asynchronously. </p> <p>In

general, the function should return once the request is initiated. If the

entire operation cannot be completed immediately, then further request processing

must occur within ISRs and DFCs, i.e. using some hardware specific mechanism

to indicate completion, or by the use of considerate poll timers to considerately

poll the device for it’s current status, with the final request completion

being done from within a DFC. The code that implements the asynchronous requests

can run within its own thread, or use one of the default threads provided

by the kernel (DFC queue thread 0). </p> <p>The underlying media driver framework

allows multiple requests to be processed simultaneously. However, other than

being able to issue multiple requests, there is no inherent support in the

media driver framework to support the handling of multiple requests, so such

functionality must be handled by the media driver itself. The underlying media

driver framework does, however, provide basic support for deferring requests

for later processing should the media driver not be capable of supporting

multiple requests. </p> <table id="GUID-A216F849-6301-5C82-8D54-40BE612770F8">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<tbody>

<row>

<entry><p>ECaps </p> </entry>

<entry><p>This is a request for information about the size, type, attributes

etc of the media. <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-F16E34E3-7DB1-3C6C-800D-173814AADC22"><apiname>TLocDrvRequest::RemoteDes()</apiname></xref> gives you

access to the object into which the media driver should put the requested

information. The object passed across is a <xref href="GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F.dita"><apiname>TLocalDriveCapsV2</apiname></xref> type,

and this is passed by the media driver subsystem in the form of a package

buffer, a <xref href="GUID-C7A094BD-846F-3ED2-8CCE-C0743DB3712A.dita"><apiname>TPckgBuf</apiname></xref> type. </p> <p>In practice, you just

need to use a simple cast to access the object. The following code fragment

is always used: </p> <codeblock id="GUID-35711E5C-5F23-5EC6-8B43-81C2168E1437" xml:space="preserve">...

if (id == DLocalDrive::ECaps)

    {

    TLocalDriveCapsV2& c = *(TLocalDriveCapsV2*)aRequest.RemoteDes();

    ...

    }

....

              </codeblock> <p>This request type is synchronous. </p> </entry>

</row>

<row>

<entry><p>ERead </p> </entry>

<entry><p>This is a request to read data from the media device asynchronously. </p> <p>You

need to start an asynchronous operation that reads <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-5D4ABE07-1186-392F-911F-5586150A5FB4"><apiname>TLocDrvRequest::Length()</apiname></xref> bytes

from the media, starting at position <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-0BF048C8-81F1-3E71-B13C-7605A6668A30"><apiname>TLocDrvRequest::Pos()</apiname></xref> on

the media. </p> <p>You transfer the data to the requesting thread's process

by calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-842F91FF-C780-3E2A-8860-8F34815452FC"><apiname>TLocDrvRequest::WriteRemote()</apiname></xref>, where the first

parameter is the source descriptor representing the data you have just read.

For example: </p> <codeblock id="GUID-80E5A231-3F69-5C33-ADE0-1E0C7674992E" xml:space="preserve">...

TPtrC8 des((const TUint8*)(iBase),len);

TInt r=iReadReq->WriteRemote(&des,0);

...

              </codeblock> <p>In this example, <codeph>iBase</codeph> is the

location of the data that has just been read in from the device, and <codeph>len</codeph> is

the length of this data. The code fragment also assumes that the data to be

returned starts at iBase, and not at some offset from iBase. </p> <p>As this

is an asynchronous operation, then when all data has been transferred, the

request must be completed by calling <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-8B9BB560-808F-3424-9638-7DED6737423E"><apiname>DMediaDriver::Complete()</apiname></xref>,

passing the original request and a completion code. </p> </entry>

</row>

<row>

<entry><p>EWrite </p> </entry>

<entry><p>This is a request to write data to the media device asynchronously. </p> <p>You

need to start an asynchronous operation that writes <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-5D4ABE07-1186-392F-911F-5586150A5FB4"><apiname>TLocDrvRequest::Length()</apiname></xref> bytes

to the media, starting at position <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-0BF048C8-81F1-3E71-B13C-7605A6668A30"><apiname>TLocDrvRequest::Pos()</apiname></xref> on

the media. </p> <p>Before doing the write, then you need to transfer the data

to be written from the requesting thread's process by calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-96B80631-AD1C-35E8-8613-0A630BD7D9E9"><apiname>TLocDrvRequest::ReadRemote()</apiname></xref>,

where the first parameter is the target descriptor. </p> <p>As this is an

asynchronous operation, then when all data has been transferred, the request

must be completed by calling <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-8B9BB560-808F-3424-9638-7DED6737423E"><apiname>DMediaDriver::Complete()</apiname></xref>,

passing the original request and a completion code. </p> </entry>

</row>

<row>

<entry><p>EFormat </p> </entry>

<entry><p>This is a request to format a section of the media asynchronously. </p> <p>The

start position of the section to be formatted can be found by calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-0BF048C8-81F1-3E71-B13C-7605A6668A30"><apiname>TLocDrvRequest::Pos()</apiname></xref>,

and the number of bytes to be formatted can be found by calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-5D4ABE07-1186-392F-911F-5586150A5FB4"><apiname>TLocDrvRequest::Length()</apiname></xref>. </p> <p>Following

a format operation, the state of the formatted section depends on the type

of media. In practice, you should access locations within the specified section,

so that bad regions can be detected and reported. </p> <p>The length of each

format request is usually based on the value of <xref href="GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F.dita#GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F/GUID-BDF05FE9-56B5-328B-B562-9F59EF14DAB2"><apiname>TLocalDriveCapsV2::iEraseBlockSize</apiname></xref>,

as returned by the <codeph>ECaps</codeph> request. If you need to adjust the

start address of the next format request, you can return a positive value

that is interpreted as indicating the actual number of bytes formatted in

the current step. This feature is useful for media that prefers format operations

to be performed on specific boundaries; for example MultiMedia Cards. </p> <p>As

this is an asynchronous operation, then when the format operation has been

done, the request must be completed by calling <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-8B9BB560-808F-3424-9638-7DED6737423E"><apiname>DMediaDriver::Complete()</apiname></xref>,

passing the original request and a completion code. </p> </entry>

</row>

<row>

<entry><p>EEnlarge </p> </entry>

<entry><p>This is a request to enlarge the accessible range of the media asynchronously.

For example, this is used on the internal RAM drive. </p> <p>Calling <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-5D4ABE07-1186-392F-911F-5586150A5FB4"><apiname>TLocDrvRequest::Length()</apiname></xref> gives

you the number of bytes by which the accessible range is to be increased. </p> <p>The

media attributes, as defined by the settings in <xref href="GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F.dita#GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F/GUID-886205BC-3234-3FDC-B17E-F9293C957097"><apiname>TLocalDriveCapsV2::iMediaAtt</apiname></xref> returned

by the <codeph>ECaps</codeph> request, must have <xref href="GUID-8F5CB589-F631-3216-9BB0-DCCF96836E4E.dita"><apiname>KMediaAttVariableSize</apiname></xref> set,

otherwise the request fails with <codeph>KErrNotSupported</codeph>. </p> <p>As

this is an asynchronous operation, then when the operation is complete, the

request must be completed by calling <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-8B9BB560-808F-3424-9638-7DED6737423E"><apiname>DMediaDriver::Complete()</apiname></xref>,

passing the original request and a completion code. </p> </entry>

</row>

<row>

<entry><p>EReduce </p> </entry>

<entry><p>This is a request to reduce the accessible range of the media asynchronously.

For example, this is used on the internal RAM drive. </p> <p>The range to

be removed is defined as <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-5D4ABE07-1186-392F-911F-5586150A5FB4"><apiname>TLocDrvRequest::Length()</apiname></xref> bytes

starting at <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-0BF048C8-81F1-3E71-B13C-7605A6668A30"><apiname>TLocDrvRequest::Pos()</apiname></xref>. In effect, the request

removes the section from <codeph>Pos()</codeph> to <codeph>Pos()</codeph> + <codeph>Length()</codeph>,

and the length is reduced by <codeph>Length()</codeph>. </p> <p>The media

attributes, as defined by the settings in <xref href="GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F.dita#GUID-414CD5E5-216F-3D97-9F04-A93B1A0EA74F/GUID-886205BC-3234-3FDC-B17E-F9293C957097"><apiname>TLocalDriveCapsV2::iMediaAtt</apiname></xref> returned

by the <codeph>ECaps</codeph> request, must have <xref href="GUID-8F5CB589-F631-3216-9BB0-DCCF96836E4E.dita"><apiname>KMediaAttVariableSize</apiname></xref> set,

otherwise the request fails with <codeph>KErrNotSupported</codeph>. </p> <p>As

this is an asynchronous operation, then when the operation is complete, the

request must be completed by calling <xref href="GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC.dita#GUID-A0D4EB25-0BA4-39EE-874B-465EB9628DCC/GUID-8B9BB560-808F-3424-9638-7DED6737423E"><apiname>DMediaDriver::Complete()</apiname></xref>,

passing the original request and a completion code. </p> </entry>

</row>

</tbody>

</tgroup>

</table> <p id="GUID-E6DF6D45-ACB1-5C0C-A4F1-02778EA69D34"><b>A simple implementation</b> </p> <codeblock id="GUID-6AABA189-4F0A-586D-B3DC-DC38F54A8721" xml:space="preserve">TInt DMyMediaDriver::Request(TLocDrvRequest&amp; aRequest)

    {

    TInt err = KErrNotSupported;

    TInt id  = aRequest.Id();

    if (id == DLocalDrive::ECaps)

        {

        TLocalDriveCapsV2& c = *(TLocalDriveCapsV2*)aRequest.RemoteDes();

        err = Caps(c);

        c.iSize = m.Drive()->iPartitionLen;

        c.iPartitionType = m.Drive()->iPartitionType;

        return(err);

        }

    if(iCurrentReq != NULL)

        {

        return(KMediaDriverDeferRequest);

        }

    iCurrentReq = &aRequest;

    switch(id)

        {

        case DLocalDrive::ERead:

            r = StartRead();

            break;

        case DLocalDrive::EWrite:

            r = StartWrite();

            break;

        case DLocalDrive::EFormat:

            r = StartErase();

            break;

        }

    if (err < 0)

        {

        iCurrentReq = NULL;

        DMediaDriver::Complete(aRequest, err);

        }

    return(err);

    }

            </codeblock> <p>This demonstrates the following behaviour: </p> <ul>

<li id="GUID-12FE8B56-D998-5FDC-B3B8-CAAD3CBDD6C8"><p>The <codeph>ECaps</codeph> request

is inherently synchronous, and must complete immediately. </p> </li>

<li id="GUID-4188EC10-8F2D-5755-BC7A-9BEB663114E5"><p>This example only handles

a single request at a time. If the media driver is busy handling a request,

it can return the value <xref href="GUID-4E76E7B3-202A-3FE1-AAF2-5B41FF13843D.dita"><apiname>KMediaDriverDeferRequest</apiname></xref> which

defers the message until the current request is complete. </p> </li>

<li id="GUID-2A148BC4-E4B8-5EF5-ACF7-50BA52E5A02E"><p>Each message is passed

on to the specific function that is responsible for handling the message.

This provides readability and ease of maintenance. </p> </li>

<li id="GUID-648C0A4B-3481-55A9-B0A4-887378B0EB7A"><p>If an error occurs,

the request is completed immediately with the specified error code. </p> </li>

</ul> <p>The following code is the implementation of the <codeph>StartWrite()</codeph> function

that initiates the asynchronous write operation. It gets the length and position

information, and then calls <codeph>DoWriteStep()</codeph>: </p> <codeblock id="GUID-B853FBC7-7A25-5A6B-8799-CB577595B461" xml:space="preserve">TInt DMyMediaDriver::StartWrite()

    {

    // Start an asynchronous write operation

    iCurrentPos = iCurrentReq->Pos();

    iCurrentLength = iCurrentReq->Length();

    TInt err = DoWriteStep();

    return(err);

    }

                </codeblock> <p> <codeph>DoWriteStep()</codeph> performs a

single write operation. In this example, a single write operation cannot exceed

the capabilities of the hardware, so the request is split up into chunks of <codeph>KMyMediaDriverWriteLength</codeph> bytes. </p> <codeblock id="GUID-3C11FDAE-EA06-5B7C-9FC5-DA2C591FFF49" xml:space="preserve">TInt DMyMediaDriver::DoWriteStep()

    {

    // Perform a single write step

    TUint8* destAddress = iBaseAddress + iCurrentPos;

    TInt writeLength = MIN(iCurrentLength, KMyMediaDriverWriteLength);

    TPtr8 des(iData, writeLength);

    TInt err = iCurrentReq->ReadRemote(&des, iCurrentPos - iCurrentReq->Pos());

    if (err != KErrNone)

        {

        return(err);

        }

        iCurrentPos += writeLength;

        iCurrentLength -= writeLength;

        TheHardware::StartWrite(iCurrentPos, writeLength, iData);

    }

                </codeblock> <p>The write operation to the hardware is performed

by <codeph>TheHardware::StartWrite()</codeph>. For most hardware, completion

is signalled by an interrupt, and the ISR handling the interrupt will queue

a DFC. This in turn can call a function like <codeph>WriteComplete()</codeph> shown

below: </p> <codeblock id="GUID-E1F615B2-E148-5C79-8F78-41407C0C2013" xml:space="preserve">TInt DMyMediaDriver::WriteComplete(TInt aResult)

    {

    // Called upon completion of the write operation

    // (ie – in DFC after completion interrupt or polled status completion)

    TBool completeRequest = (iCurrentLength == 0) || (aResult ! = KErrNone);

    if(!completeRequest)

        {

        // There is more data remaining, so write some more data…

        if((aResult = DoWriteStep()) != KErrNone)

            {

            completeRequest = ETrue;

            }

        }

    if(completeRequest)

        {

        // We are all done, or an error occurred…

        DMediaDriver::Complete(iCurrentReq, aResult);

        iCurrentReq = NULL;

        }

    }

                </codeblock> <p> <codeph>WriteComplete()</codeph> is an example

of a callback or completion function, and shows how a single request may be

broken up into a number of smaller chunks. The write request is only completed

when the entire write operation is complete or an error occurs. </p> <p>This

simple example has demonstrated how a simple <codeph>EWrite</codeph> request

may be handled. The <codeph>ERead</codeph> and <codeph>EFormat</codeph> requests

are handled in exactly the same way, taking into account the message parameters

shown in the previous table. </p> <p id="GUID-2FF89E43-6F12-5A63-A8A5-298667C5D7A2"><b>Issues about physical addresses</b> </p> <p>If

the media driver can use physical addresses, you need to be aware of a number

of issues. </p> <ul>

<li id="GUID-3CCA7A0E-B245-5221-AA0F-AA9CA1F33869"><p> <i>The address scheme

used by the hardware</i>  </p> <p>All media devices have a minimum number

of bytes that they can transfer. For example, the architecture of some memory

card types requires data transfer in blocks of 512 bytes. To read one byte

from this type of media device, the media driver must read a block of 512

bytes and extract the byte from the block. To write one byte to a media device,

the media driver must read a block of 512 bytes, change the content of the

byte, and write the block to the media device. </p> </li>

<li id="GUID-6AA344A1-607A-5220-AE65-70F1A5B35967"><p> <i>Data transfer smaller

than the minimum size</i>  </p> <p>If the local media subsystem receives a

request to transfer data with a length smaller than the minimum transfer size,

the local media subsystem does not make a physical address available to the

media driver. A call to <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-DD6773B4-9EF5-322F-B53D-29174DF3B3BF"><apiname>TLocDrvRequest::IsPhysicalAddress()</apiname></xref> returns

false. It is considered unsafe to give access to the physical data surrounding

the requested memory location. </p> </li>

<li id="GUID-B5CA6F1A-CCD3-5DA0-9297-547F0E80506A"><p> <i>Data transfer not

aligned to the media device block boundary</i>  </p> <p>If the local media

subsystem receives a request to transfer data, and the address on the media

device is <i>not aligned</i> to the media device block boundary, you need

to adopt the technique suggested below. The local media subsystem will make

the physical address available to the media driver. A call to <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-DD6773B4-9EF5-322F-B53D-29174DF3B3BF"><apiname>TLocDrvRequest::IsPhysicalAddress()</apiname></xref> returns

true. </p> <p>Consider the following case. A request has been made to read

1024 bytes from a media device that has a block size of 512 bytes. The 1024

bytes start at offset +256 on the media device. </p> <fig id="GUID-30EA5683-9B12-59D6-88EF-21F4E84988B3">

<image href="GUID-12CD8E91-4102-5253-A7DE-E5436028764F_d0e418369_href.png" placement="inline"/>

</fig> <p>To get the first 256 bytes, you must read the first block of 512

bytes from the media device. This can corrupt the physical memory passed in

the I/O request. The solution is to read the first block from the media device

into an intermediate buffer. Copy the 256 bytes from that buffer into the

physical memory passed in the I/O request. </p> <p>To get the last 256 bytes,

you must read the third block of 512 bytes from the media device into the

intermediate buffer. Copy the 256 bytes from that buffer into the correct

position in the physical memory passed in the I/O request. </p> <p>The middle

512 bytes are aligned on the media device block boundary. The media driver

can read this data into the correct position in the physical memory passed

in the I/O request. </p> </li>

<li id="GUID-27C1D94D-09CB-5C70-94DF-B1FDC8784DE9"><p> <i>Scatter/Gather DMA

controllers</i>  </p> <p>DMA controllers can support the Scatter/Gather mode

of operation. Each request in this mode of operation consists of a set of

smaller requests chained together. This chain of requests is called the Scatter/Gather

list. Each item in the list consists of a physical address and a length. </p> <p>Use <xref href="GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C.dita#GUID-D84A9903-AE0F-3F54-8833-E8956A88E26C/GUID-9879145B-D996-327E-87F6-3B8337A86A56"><apiname>TLocDrvRequest::GetNextPhysicalAddress()</apiname></xref> to

help you populate the Scatter/Gather list. </p> <p>The following code fragment

shows how you do this. The example assumes that the DMA controller supports

a Scatter/Gather list with an unlimited number of entries. In practice, the

number of entries in the list is finite. </p> <codeblock id="GUID-51D14E43-D388-507C-826E-8249EAA83287" xml:space="preserve">TPhysAddr physAddr; 

   TInt physLength;

   TInt err = KErrNone;