case SubPowerDownComplete:
			{					// SubPowerDownComplete
			if (status == -1)
				status = STATUS_SUCCESS; // don't actually care, since called from PoCompletionRoutine

			if (NT_SUCCESS(ctx->status))
				{
				SETSTATE(SysPowerDownPending);
				action = ForwardMainIrp;
				}
			else
				action = CompleteMainIrp; // D-state IRP failed, so fail S-state IRP too
			
			continue;
			}					// SubPowerDownComplete

		///////////////////////////////////////////////////////////////////////
		// DevPowerUpComplete is the action for a MainIrpComplete event in the
		// DevPowerUpPending state. This should be called from MainCompletionRoutine
		// when a device power-up IRP finishes in the lower layers.

		case DevPowerUpComplete:
			{					// DevPowerUpComplete

			// If this IRP failed, or if we're just dealing with a query, we're done.

			if (!NT_SUCCESS(ctx->status) || stack->MinorFunction != IRP_MN_SET_POWER)
				{
				action = CompleteMainIrp;
				continue;
				}

			status = STATUS_MORE_PROCESSING_REQUIRED; // defer completion of the main IRP while we restore context

			ctx->oldpower = pdx->devpower;
			pdx->devpower = stack->Parameters.Power.State.DeviceState;
			
			// TODO Replace the "if (FALSE)" statement block immediately below with code
			// to initiate an asynchronous process to restore device context information
			// that was saved when power was lost. ctx->oldpower is the previous power
			// state, and pdx->devpower is the new power state. When this process finishes,
			// call SendAsyncNotification with "ctx" as the argument

			if (FALSE)
				{				// restore context
				SETSTATE(ContextRestorePending);
				// right here is where you start restoring context data
				break;
				}				// restore context

			action = ContextRestoreComplete;
			continue;
			}					// DevPowerUpComplete

		///////////////////////////////////////////////////////////////////////
		// ContextRestoreComplete is the last action for a device set power up
		// operation. It's ordinarily reached when GenericSaveRestoreComplete
		// signals a MainIrpComplete event from the ContextRestorePending state.
		// It can also be reached directly from DevPowerUpComplete when there is
		// no context restore function.

		case ContextRestoreComplete:
			{					// ContextRestoreComplete
			if (event == AsyncNotify)
				status = STATUS_SUCCESS; // doesn't actually matter
			action = CompleteMainIrp;

			// If the device IRP failed, just go ahead and let it complete. If we've
			// successfully resumed to a sleeping state (> D0), skip restarting the
			// substantive IRP queue and complete the IRP as well.

			if (!NT_SUCCESS(ctx->status) || pdx->devpower != PowerDeviceD0)
				continue;

			ASSERT(stack->MinorFunction == IRP_MN_SET_POWER); // query should have gone directly to CompleteMainIrp from DevPowerUpComplete

			continue;
			}					// ContextRestoreComplete

		///////////////////////////////////////////////////////////////////////
		// SaveContext initiates a context save operation if necessary. This will
		// be the second action for a new device set-power IRP.

		case SaveContext:
			{					// SaveContext
			ASSERT(stack->MinorFunction == IRP_MN_SET_POWER);
			DEVICE_POWER_STATE devpower = stack->Parameters.Power.State.DeviceState;

			// TODO Replace the following block of code with code that initiates
			// an asynchronous process to save an relevant device context. When
			// that process finishes, call SendAsyncNotification with "ctx" as
			// the argument.

			if (FALSE && devpower > pdx->devpower)
				{				// save context
				SETSTATE(ContextSavePending);
				// put code here to start saving context
				break;
				}				// save context

			action = ContextSaveComplete;
			continue;
			}					// SaveContext

		///////////////////////////////////////////////////////////////////////
		// ContextSaveComplete is the action for an AsyncNotify event in the
		// ContextSavePending state. It should be entered from GenericSaveRestoreComplete,
		// which in turn should have been called by the client driver when its
		// context save operation finished. It can also be entered directly from
		// SaveContext when there is no context save routine.

		case ContextSaveComplete:
			{					// ContextSaveComplete
			if (event == AsyncNotify)
				status = STATUS_SUCCESS;	// doesn't actually matter in this case

			SETSTATE(DevPowerDownPending);
			action = ForwardMainIrp;

			ASSERT(stack);
			DEVICE_POWER_STATE devpower = stack->Parameters.Power.State.DeviceState;
			if (devpower <= pdx->devpower)
				continue;		// no actual change in device power

			ASSERT(stack->MinorFunction == IRP_MN_SET_POWER);

			pdx->devpower = devpower;

			continue;
			}					// ContextSaveComplete

		///////////////////////////////////////////////////////////////////////
		// DevQueryUpComplete is the action for a MainIrpComplete event in the
		// DevQueryUpPending state. This should be called by MainCompletionRoutine
		// when a device query-power-up IRP completes. We don't expect to ever get this
		// kind of a query, by the way, but we should handle it nontheless.

		case DevQueryUpComplete:
			{					// DevQueryUpComplete
			if (NT_SUCCESS(ctx->status))
				{				// ask client if change okay

				// TODO replace the FALSE immediately below with some non-blocking test
				// to see if it's okay to restore power. It would be very unusual to
				// say "no". In making the test, pdx->devpower is the current power
				// state and stack->Parameters.Power.State.DeviceState is the
				// proposed new state.

				if (FALSE)
					ctx->status = STATUS_UNSUCCESSFUL; // fail the query
				}				// ask client if change okay

			action = CompleteMainIrp;
			continue;
			}					// DevQueryUpComplete

		///////////////////////////////////////////////////////////////////////
		// DevQueryDown is the second action (after TriageNewIrp) for a device
		// query-power that specifies less than or equal to the current device
		// power state.

		case DevQueryDown:
			{					// DevQueryDown
			DEVICE_POWER_STATE devpower = stack->Parameters.Power.State.DeviceState;

			// TODO replace the FALSE immediately below with some non-blocking test
			// to see if it's okay to remove power. In making the test, pdx->devpower
			// is the current power state and devpower is the proposed new state.

			if (devpower > pdx->devpower && FALSE)
				{				// fail the query
				ctx->status = STATUS_UNSUCCESSFUL;
				action = DevQueryDownComplete;
				continue;
				}				// fail the query

			SETSTATE(DevQueryDownPending);
			action = ForwardMainIrp;
			continue;
			}					// DevQueryDown

		///////////////////////////////////////////////////////////////////////
		// DevQueryDownComplete is the action for a MainIrpComplete event in the
		// DevQueryDownPending state. It can be reached from MainCompletionRoutine
		// or directly from DevQueryDown.

		case DevQueryDownComplete:
			{					// DevQueryDownComplete

			action = CompleteMainIrp;
			continue;
			}					// DevQueryDownComplete

		///////////////////////////////////////////////////////////////////////
		// InvalidAction is the action for any unexpected event. It should never occur.

		case InvalidAction:
		default:
			ASSERT(FALSE);
			status = STATUS_UNSUCCESSFUL;
			break;
			}					// perform next action

		break;					// for cases that "break" from the switch
		}						// handle this event

	// Check to make sure the state got changed before we exit
		
	ASSERT(nextstate != originalstate);

	// Check to make sure a valid status will be returned

	ASSERT(status != -1);

	return status;
	}							// HandlePowerEvent

///////////////////////////////////////////////////////////////////////////////

NTSTATUS MainCompletionRoutine(PDEVICE_OBJECT junk, PIRP Irp, PPOWCONTEXT ctx)
	{							// MainCompletionRoutine
	ctx->status = Irp->IoStatus.Status;
	return HandlePowerEvent(ctx, MainIrpComplete);
	}							// MainCompletionRoutine

VOID PoCompletionRoutine(PDEVICE_OBJECT junk, UCHAR fcn, POWER_STATE state, PPOWCONTEXT ctx, PIO_STATUS_BLOCK pstatus)
	{							// PoCompletionRoutine
	ctx->status = pstatus->Status;
	HandlePowerEvent(ctx, AsyncNotify);
	}							// PoCompletionRoutine

VOID PassivePowerCall(PIRP Irp)
	{							// PassivePowerCall
	PoCallDriver(IoGetNextIrpStackLocation(Irp)->DeviceObject, Irp);
	}							// PassivePowerCall

NTSTATUS SafePoCallDriver(PDEVICE_OBJECT DeviceObject, PIRP Irp)
	{							// SafePoCallDriver

	// If running in Win2K, or if Win98 and already at PASSIVE_LEVEL, just call
	// PoCallDriver.

	if (!win98 || KeGetCurrentIrql() == PASSIVE_LEVEL)
		return PoCallDriver(DeviceObject, Irp);
	
	// Win98's PoCallDriver is the same as IoCallDriver, and it won't do anything to
	// present the IRP at passive level if we're currently above. Build a work queue
	// item in the DriverContext field of the IRP and queue the work item so we
	// can present the IRP properly. Boy, is this something we shouldn't have to
	// worry about!

	IoMarkIrpPending(Irp);		// be sure it's marked pending
	IoGetNextIrpStackLocation(Irp)->DeviceObject = DeviceObject; // so PassivePowerCall can find it

	PWORK_QUEUE_ITEM item = (PWORK_QUEUE_ITEM) Irp->Tail.Overlay.DriverContext;
	ExInitializeWorkItem(item, (PWORKER_THREAD_ROUTINE) PassivePowerCall, (PVOID) Irp);
	ExQueueWorkItem(item, DelayedWorkQueue);

	return STATUS_PENDING;
	}							// SafePoCallDriver