DEVICE DRIVERS AND EXTENSIONS in .NET

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LDD name. These are usually drivers that don t rely on the kernel s automatic PDD matching framework, and I ll talk about this later. So, in our simple serial driver, the Install() functions would look something like this:
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// Simple Serial LDD _LIT(KLddName,"Serial"); TInt DSimpleSerialLDD::Install() { return(SetName(&KLddName)); } // Simple 16550 Uart PDD _LIT(KPddName,"Serial.16550"); TInt DSimple16550PDD::Install() { return(SetName(&KPddName)); }
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I ve already mentioned that the Install() function may also be used to perform any initialization that should take place when the driver is rst loaded. For example, the driver may create a new kernel thread, allocate shared memory or check for the presence of a required kernel extension or hardware resource.
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12.4.4.2 Verifying that devices are loaded
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Symbian OS provides iterator classes to enable applications to identify which kernel objects are currently present in the system. In particular, TFindPhysicalDevice and TFindLogicalDevice may be used to identify which device drivers are currently loaded:
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class TFindPhysicalDevice : public TFindHandleBase { public: inline TFindPhysicalDevice(); inline TFindPhysicalDevice(const TDesC& aMatch); IMPORT_C TInt Next(TFullName& aResult); };
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These are derived from TFindHandleBase, a base class which performs wildcard name matching on kernel objects contained within object containers, from which a number of classes are derived to nd speci c types of kernel objects:
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class TFindHandleBase { public:
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IMPORT_C TFindHandleBase(); IMPORT_C TFindHandleBase(const TDesC& aMatch); IMPORT_C void Find(const TDesC& aMatch); inline TInt Handle() const; protected: TInt NextObject(TFullName& aResult,TInt aObjectType); protected: /** The find-handle number. */ TInt iFindHandle; /** The full name of the last kernel-side object found. */ TFullName iMatch; };
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Each iterator class provides its own implementation of Next, which calls the protected NextObject method providing the ID of the container to be searched:
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EXPORT_C TInt TFindPhysicalDevice::Next(TFullName &aResult) { return NextObject(aResult,EPhysicalDevice); }
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For example, to nd all physical devices present in the system, we would use TFindPhysicalDevice as follows:
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TFindPhysicalDevice findHb; findHb.Find(_L( * )); TFullName name; while (findHb.Next(name)==KErrNone) RDebug::Print(name);
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This is precisely the mechanism used by the text window server s PS command, which produces the output shown in Figure 12.6.
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Figure 12.6 Using the text shell s command
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12.4.4.3 Unloading the driver
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A user-side application can unload an LDD or PDD using one of the following APIs:
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TInt User::FreeLogicalDevice(const TDesC &aDeviceName) TInt User::FreePhysicalDevice(const TDesC &aDeviceName)
Note that an object name (aDeviceName) is used in this instance, rather than the le name that was used when loading the device. These functions enter the kernel via the executive call:
TInt ExecHandler::DeviceFree(const TDesC8& aName, TInt aDeviceType)
The aDeviceType parameter identi es the necessary object container (EPhysicalDevice or ELogicalDevice) within which the object is located by name. If the kernel nds the object, it closes it, which will result in deletion of the object and its code segment, if it is not in use by another thread:
DLogicalDevice:: DLogicalDevice() { if (iCodeSeg) { __DEBUG_EVENT(EEventUnloadLdd, iCodeSeg); iCodeSeg->ScheduleKernelCleanup(EFalse); } }
The function call ScheduleKernelCleanup(EFalse) unloads the associated DLL with module reason KModuleEntryReasonProcessDetach, ensuring that the any static data initialized at DLL load time is destroyed. The EFalse parameter indicates that the code segment is not to be immediately destroyed (since we are still using the code to run the destructor), but is to be added to the garbage list and scheduled for deletion when the null thread next runs.
12.4.5 Opening the device driver
In the previous section, I discussed how device drivers are loaded, creating LDD and PDD factory objects. The next step in using a device driver is to open a channel through which requests can be made. User-side code does this by making a call to RBusLogicalChannel::DoCreate(). (In reality, a client cannot call this method directly, since it is protected. It is called indirectly, via a driver-speci c wrapper function, usually named Open(), although this doesn t affect our current discussion.)
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inline TInt DoCreate(const TDesC& aDevice, const TVersion& aVer, TInt aUnit, const TDesC* aDriver, const TDesC8* anInfo, TOwnerType aType=EOwnerProcess, TBool aProtected=EFalse);
The client provides the name of the LDD (again, giving the object name that uniquely identi es the LDD factory), the supported version number, the unit number, an optional PDD name and an optional extra information block. For example:
DoCreate(_L("Serial"), version, KUnit0, NULL, NULL); DoCreate(_L("Serial"), version, KUnit0, _L( 16550 ), NULL);
These examples demonstrate the two different mechanisms that the kernel device driver framework provides for opening channels to device drivers: 1. Automatic search for a suitable physical device (no PDD name is speci ed) 2. User-speci ed physical device (a PDD name is provided). I will discuss both of these methods in the following sections, in which I will show how channels are created using LDD and PDD factory objects.