TYPICAL POWER MANAGEMENT in .NET

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TYPICAL POWER MANAGEMENT
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PowerDown() to Off or Channel closure
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Example serial comms driver state machine
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The state diagram shown in Figure 15.7 applies.
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15.3.2.1 Thread and synchronization issues
The driver power management functions execute in different contexts: 1. The power manager s PowerUp() and PowerDown() are called from the thread of the user-side component responsible for the system transition 2. Requests from a client (including closing the channel) are issued from the client s thread but their servicing and their completion execute in the driver s thread. Channel opening executes in the client s context 3. The inactivity timer s expiration generates an interrupt 4. The callbacks that are called when entering or leaving CpuIdle() execute in the null thread. Thus, we must take some care to guarantee that execution is performed in the right sequence: We must protect both the peripheral s and the power resource s state changes against the preemption of the executing thread
POWER MANAGEMENT
The power manager s PowerUp() and PowerDown() must schedule DFCs to execute in the driver s thread The inactivity timer interrupt must schedule a DFC to execute in the driver s thread Transitions to the off state, or to and from the standby state, involve the calling of other power handlers and take some time: it might happen that a request comes in, or the null thread gets to run, after our driver s power handler moves to its low power state, and before the CPU reaches that state. This might also happen after the CPU wakes up but before our driver s power handler moves the peripheral back to the active state. Service requests and the CpuIdle() entry callback must check the current power state We must cancel the inactivity timer and the ensuing DFC on every state change, apart from when moving from the idle state to the retention state (since this is caused by its own expiration) The CpuIdle() entry and exit callbacks run with interrupts disabled (as I mentioned in Section 15.2.2.1). They cannot be preempted, and always run in sequence, even if the CPU never reaches the retention state The CPU idle (null) thread may run while a request is being serviced (for example, if the driver blocks waiting on a hardware event), or at any time during the power down or power up sequence. The driver s CpuIdle() entry callback needs to check if the peripheral state is idle When the client closes the channel to the driver, the kernel sends a request as a kernel-side message to the driver that needs to be completed before the driver object is destructed. The completion of a kernel-side message may block, so the power-down or powerup DFCs, or the null thread, may run between the driver shutting down and the driver object (and the associated power handler) being destructed. We must check for this and skip any operations that result in attempting to operate on a peripheral that has already powered off.
15.3.2.2 Class de nitions
// COMM.H #include <xxxpower.h> // platform specific power definitions including power controller, Resource Manager #include <kpower.h> // framework power definition including power handlers
TYPICAL POWER MANAGEMENT
/// ... other include files typedef void (*TCpuidleInCallBack)(TAny* aPtr); typedef void (*TCpuidleOutCallBack)(TAny* aPtr); class DSerialDriverPowerHandler : public DPowerHandler { enum TPowerState { EActive, EIdle, ERetention, EEtandby, EOff }; public: // from DPowerHandler void PowerUp(); void PowerDown(TPowerState); public: DSerialDriverPowerHandler(DChannelSerialDriver* aChannel); public: void RegisterCpuIdleCallback(TBool aRegister); public: DChannelSerialDriver* iChannel; XXXResourceManager* iResourceManager; DXXXPowerController* iPowerController; DPowerHandler* iNextCi; TCpuIdleInCallBack iEnteridleCallback; TCpuIdleOutCallBack iLeaveidleCallback; TPowerState iPowerState; TBool iStandby; }; class DChannelSerialDriver : public DLogicalChannel { public: enum TState {EOpen,Eactive,EClosed}; public: DChannelSerialDriver(); DChannelSerialDriver(); // ... other Serial Driver public methods protected: virtual TInt DoCreate(TInt aUnit, const TDesC8* anInfo, const TVersion& aVer); virtual void HandleMsg(TMessageBase* aMsg); // entry point for all requests void Complete(TInt aMask, TInt aReason); // exit point for all requests void Shutdown(TBool astandby); // if ETrue, going to standby void MoveToActive(); void MoveToRetention(); void DoPowerUp(); // ... private: static static static static other Serial Driver protected methods void void void void PowerUpDfc(TAny* aPtr); PowerDownDfc(TAny* aPtr); TimerCallBack(TAny* aPtr); TimerDfcFn(TAny* aPtr);