Version

An LDD and a PDD each have a version number which helps to identify the +interface. In order to communicate, an LDD and a PDD must have the same version +number.

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; + ... + }