Version

Version definition

Each LDD and PDD has their own version number. LDDs and PDDs must set their version numbers in their respective factory objects, using a TVersion object. TVersion specifies a major number, a minor number and a build number.

A version number defines the interface version supported by the LDD or PDD. It is used to check that an LDD and PDD are compatible. It is also checked against the version requested by a client when it opens a channel.

The following shows how the example device drivers set their version numbers:

inline TVersion RExDriverChannel::VersionRequired()
    {    
    return (TVersion(EUartMajorVersionNumber,
            EUartMinorVersionNumber,
            EUartBuildVersionNumber));
    }

// LDD Factory object Constructor
DExDriverLogicalDevice::DExDriverLogicalDevice ()
    {
    iVersion = RExDriverChannel::VersionRequired();
    }

// PDD Factory object Constructor
DExH4PhysicalDevice::DExH4PhysicalDevice ()
    {        
    iVersion= RExDriverChannel::VersionRequired();
    }

Version compatibility

The Kernel provides the Kern::QueryVersionSupported() API to enforce a consistent set of rules for checking version compatibility. It returns true if one of the following conditions is true:

• the major version of the client is less than the major version of the driver.

• the major version of the client is equal to the major version of the driver, and the minor version of the client is less than or equal to the minor version of the driver.

DLogicalChannel::DoCreate() typically checks the client version against the driver using this API.

// Logical Channel Second stage constructor
TInt DExDriverLogicalChannel::DoCreate(TInt /*aUnit*/, const TDesC8* 
/*anInfo*/, const TVersion& aVer)
    {
    ...
    // Version check
    if(!Kern::QueryVersionSupported(RExDriver::VersionRequired(),
aVer))
    return KErrNotSupported;
    ...
    }

When the device framework searches for a corresponding PDD factory object for an LDD, it calls DPhysicalDevice::Validate() on each matching PDD factory object, passing the unit number and the optional extra information block. The first PDD to return KErrNone is accepted as the required PDD.

The example PDD's Validate() implementation checks the version of the LDD against the PDD, using the Kern::QueryVersionSupported() API:

// PDD: Validate
TInt DExH4PhysicalDevice::Validate(TInt aUnit, const TDesC8* 
/*aInfo*/, const TVersion& aVer)    
    {
    ...
    // Version check
    if (!Kern::QueryVersionSupported(iVersion,aVer))    
        return KErrNotSupported;
    ...
    }