In S60 3rd edition FP1 SDK (Symbian 9.2) CMMFDevSound is not inherited from MMMFHwDeviceObserver as it was in earlier version (Symbian 8.0a).
Also it is written that "This item is not part of the S60 3rd Edition SDK for Symbian OS, Supporting Feature Pack 1, for C++."

we know that CMMFDevSound owns the hardware device(CMMFHwDevice derived object). The devsound calls Start method of hwdevice. and this starts the buffer flow between devsound and hwdevice.

In case of audio playback, hwdevice calls FillThisHwBuffer of its observer (i.e. MMMFHwDeviceObserver). then devsound calls the ThisHwBufferFilled on the hwdevice.

My doubt is that FillThisHwBuffer API is a pure virtual function which should be implemented in it's (i.e. MMMFHwDeviceObserver) derived class. Earlier it's implementation was present in CMMFDevSound because it was inherited from MMMFHwDeviceObserver class.

And since in latest version this is not the case is there any alternative way DevSound interact with HwDevice.