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If initialization is successful, the kernel adds the newly created logical channel into the ELogicalChannel object container, and creates a handle, which it returns to the user-side client. If it is not, the kernel closes the logical channel and any associated physical device and returns a suitable error. Note: Being a handle to a kernel object, the client side RBusLogicalChannel handle inherits the standard handle functionality described in 5, Kernel Services. By default, the kernel creates an RBusLogicalChannel handle with ELocal and EOwnerProcess attributes, thus restricting usage to the process that opened the channel. Protection may be promoted to EProtected by specifying aProtected = ETrue in RBusLogicalChannel::DoCreate. This will allow the handle to be shared with other processes using the IPC mechanisms available for handle sharing. The handle may never be promoted to an EGlobal object.
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12.4.5.2 Creating the physical device the PDD factory
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Some LDDs don t require a physical device to be present (two examples being the local media sub-system which takes responsibility for loading its own media drivers and the USB controller which communicates directly with a kernel extension). But the majority of LDDs do need a PDD, since most device drivers rely on hardware with more than one possible variant. A physical channel is nothing more than a simple DBase-derived object, and as such has an interface that is determined only by the LDD with which it is associated. (Contrast this with the logical channel, which must be derived from DLogicalChannelBase and conforms to a globally de ned interface). It is the responsibility of the DphysicalDevicederived PDD factory to validate and create the physical channel:
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class DPhysicalDevice : public DObject { public: enum TInfoFunction { EPriority=0, }; public: IMPORT_C virtual DPhysicalDevice(); IMPORT_C virtual TBool QueryVersionSupported(const TVersion& aVer) const; IMPORT_C virtual TBool IsAvailable(TInt aUnit, const TDesC8* aInfo) const; virtual TInt Install() =0; virtual void GetCaps(TDes8& aDes) const =0; virtual TInt Create(DBase*& aChannel, TInt aUnit, const TDesC8* aInfo, const TVersion& aVer) =0; virtual TInt Validate(TInt aUnit, const TDesC8* aInfo, const TVersion& aVer) =0;
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DEVICE DRIVERS AND EXTENSIONS
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IMPORT_C virtual TInt Info(TInt aFunction, TAny* a1); public: TVersion iVersion; TUint iUnitsMask; DCodeSeg* iCodeSeg; };
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Notice that this looks very similar to DLogicalDevice not surprising since they perform an almost identical task. However, there are a few differences in the physical device: iParseMask does not exist A Validate() method must be provided to support the logical device in searching for suitable PDDs. (I ll show an example implementation of this later) An optional Info() method may be provided to provide additional device-speci c information about the driver. This is currently only used by media drivers (as you can see in 13, Peripheral Support ). Now, let s look at PDD loading in a little more detail.
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User-speci ed PDD If a PDD name was supplied in the call to RBusLogicalChannel::DoCreate(), the kernel rst validates the name to ensure that it is a match for the logical channel (that is, it compares the supplied <ldd>.<pdd> name with the wildcard string <ldd>.* ). If the name is valid, the kernel uses it to locate the corresponding DPhysicalDevice object in the EPhysicalDevice container. It then calls the Validate() method on this object, passing the unit number, optional extra information block and version number. This is the PDD s opportunity to verify that the version number matches that of the requesting logical channel, and that the requested unit number is supported:
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TInt DSimpleSerialPDD::Validate(TInt aUnit, const TDesC8* /*anInfo*/, const TVersion& aVer) { if(!Kern::QueryVersionSupported(iVersion,aVer) return KErrNotSupported; if (aUnit<0 || aUnit>=KNum16550Uarts) return KErrNotSupported; return KErrNone; }
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Automatic search for PDD Alternatively, if the user-side does not provide a PDD name, but the logical device requires a PDD to be present, then the kernel makes a wildcard
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