Creating the logical channel the LDD factory in Visual Studio .NET

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12.4.5.1 Creating the logical channel the LDD factory
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When you call RBusLogicalChannel::DoCreate(), it performs an executive call to create the kernel-side instance of a logical channel (DLogicalChannelBase) before initializing the client-side handle:
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EXPORT_C TInt RBusLogicalChannel::DoCreate( const TDesC& aLogicalDevice, const TVersion& aVer, TInt aUnit, const TDesC* aPhysicalDevice, const TDesC8* anInfo, TInt aType) { TInt r = User::ValidateName(aLogicalDevice); if(KErrNone!=r) return r; TBuf8<KMaxKernelName> name8; name8.Copy(aLogicalDevice); TBuf8<KMaxKernelName> physicalDeviceName; TChannelCreateInfo8 info; info.iVersion=aVer; info.iUnit=aUnit;
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if(aPhysicalDevice) { physicalDeviceName.Copy(*aPhysicalDevice); info.iPhysicalDevice = &physicalDeviceName; } else info.iPhysicalDevice = NULL; info.iInfo=anInfo; return SetReturnedHandle(Exec::ChannelCreate(name8, info, aType),*this); }
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The info parameter is of type TChannelCreateInfo, which encapsulates the user-supplied version, unit number and optional information block:
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class TChannelCreateInfo { public: TVersion iVersion; TInt iUnit; const TDesC* iPhysicalDevice; const TDesC8* iInfo; };
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The channel creation mechanism in Exec::ChannelCreate makes use of the DLogicalDevice and DPhysicalDevice factory objects that the kernel created when it loaded the device drivers. The logical device is de ned in kernel.h as follows:
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class DLogicalDevice : public DObject { public: IMPORT_C virtual DLogicalDevice(); IMPORT_C virtual TBool QueryVersionSupported( const TVersion& aVer) const; IMPORT_C virtual TBool IsAvailable(TInt aUnit, const TDesC* aDriver, const TDesC8* aInfo) const; TInt ChannelCreate(DLogicalChannelBase*& pC, TChannelCreateInfo& aInfo); TInt FindPhysicalDevice(DLogicalChannelBase* aChannel, TChannelCreateInfo& aInfo); virtual TInt Install()=0; virtual void GetCaps(TDes8& aDes) const =0; virtual TInt Create(DLogicalChannelBase*&aChannel)=0; public: TVersion iVersion;
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TUint iParseMask; TUint iUnitsMask; DCodeSeg* iCodeSeg; TInt iOpenChannels; };
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This is an abstract base class a device driver must provide an implementation of the GetCaps(), Create() and Install() methods, as these are used by the framework when creating the channel. To create a channel, the kernel-side executive handler, ExecHandler::ChannelCreate, rst uses the supplied LDD name to search the ELogicalDevice container for an associated DLogicalDevice factory object. If it nds one, it increments the factory s instance count before validating the supplied unit number against the value of the KDeviceAllowUnit ag in iParseMask, using the following rules: 1. If the device supports unit numbers, the unit number must be within the range of 0 to KMaxUnits (32). 2. If the device does not support unit numbers, the aUnit parameter must be KNullUnit. You need to initialize iVersion and iParseMask in the constructor of your DlogicalDevice-derived LDD factory to determine how your device driver is loaded. For example, if my serial driver needs the client to specify a unit number and the relevant PDD to be present in the system, I would code the constructor like this:
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DSimpleSerialLDD::DSimpleSerialLDD() { iParseMask = KDeviceAllowPhysicalDevice | KDeviceAllowUnit; iVersion = TVersion(KCommsMajorVersionNumber, KCommsMinorVersionNumber, KCommsBuildVersionNumber); }
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The following table summarizes the usage of iVersion and iParseMask: iVersion The interface version supported by this LDD. This is used to check that an LDD and PDD are compatible, so you should increment it if the interface changes. The version checking API, Kern::QueryVersionSupported(), assumes that clients requesting old versions will work with a newer version, but clients requesting new versions will not accept an older version.
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iParseMask
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This is a bit mask indicating a combination of: KDeviceAllowPhysicalDevice The LDD requires an accompanying PDD KDeviceAllowUnit The LDD accepts a unit number at channel creation time KDeviceAllowInfo The LDD accepts additional device-speci c info at channel creation time KDeviceAllowAll A combination of all of these.
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iUnitsMask
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No longer used by the LDD; present for legacy reasons.
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Once the factory object has been identi ed and its capabilities validated, the kernel calls the driver s channel factory function, DLogicalDevice::Create(). This function is responsible for creating an instance of the logical channel (derived from DLogicalChannelBase) through which all subsequent requests to the driver will be routed:
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TInt DSimpleSerialLDD::Create(DLogicalChannelBase*& aChannel) { aChannel = new DSimpleSerialChannel; return aChannel KErrNone : KErrNoMemory; }
The kernel returns a pointer to the newly created channel to the framework via a reference parameter, returning an error if it is unable to create the channel. The framework stores a pointer to the DLogicalDevice that created the channel in the channel s iDevice eld (so that its reference count may be decremented when the channel is eventually closed), and increments iOpenChannels. If the logical device speci es that it needs a PDD (indicated by the KDeviceAllowPhysicalDevice ag in iParseMask), then the kernel locates a suitable PDD factory, which is used to create the devicespeci c physical channel I will cover this in more detail in the next section. The kernel stores a pointer to the newly created physical channel in the iPdd member of the logical channel. The kernel framework will now initialize the newly created DlogicalChannelBase-derived object by calling DLogicalChannelBase::DoCreate(), passing in the information contained in the TChannelCreateInfo package supplied by the user. This is the logical channel s opportunity to validate the supplied parameters, allocate additional resources and prepare the hardware for use.