// lower drivers failed this Irp
    //

    if(!NT_SUCCESS(ntStatus)) {

        PoStartNextPowerIrp(Irp);

        IsoUsb_DbgPrint(3, ("SysPoCompletionRoutine::"));
        IsoUsb_IoDecrement(DeviceExtension);

        return STATUS_SUCCESS;
    }

    //
    // ..otherwise update the cached system power state (IRP_MN_SET_POWER)
    //

    if(irpStack->MinorFunction == IRP_MN_SET_POWER) {

        DeviceExtension->SysPower = irpStack->Parameters.Power.State.SystemState;
    }

    //
    // queue device irp and return STATUS_MORE_PROCESSING_REQUIRED
    //

    SendDeviceIrp(DeviceObject, Irp);

    IsoUsb_DbgPrint(3, ("SysPoCompletionRoutine - ends\n"));

    return STATUS_MORE_PROCESSING_REQUIRED;
}

VOID
SendDeviceIrp(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP SIrp
    )
/*++

Routine Description:

    This routine is invoked from the completion routine of the system power
    irp. This routine will PoRequest a device power irp. The system irp is
    passed as a context to the the device power irp.

Arguments:

    DeviceObject - pointer to device object
    SIrp - system power irp.

Return Value:

    None

--*/
{
    NTSTATUS                  ntStatus;
    POWER_STATE               powState;
    PDEVICE_EXTENSION         deviceExtension;
    PIO_STACK_LOCATION        irpStack;
    SYSTEM_POWER_STATE        systemState;
    DEVICE_POWER_STATE        devState;
    PPOWER_COMPLETION_CONTEXT powerContext;

    //
    // initialize variables
    //

    irpStack = IoGetCurrentIrpStackLocation(SIrp);
    systemState = irpStack->Parameters.Power.State.SystemState;
    deviceExtension = (PDEVICE_EXTENSION) DeviceObject->DeviceExtension;

    IsoUsb_DbgPrint(3, ("SendDeviceIrp - begins\n"));

    //
    // Read out the D-IRP out of the S->D mapping array captured in QueryCap's.
    // we can choose deeper sleep states than our mapping but never choose
    // lighter ones.
    //

    devState = deviceExtension->DeviceCapabilities.DeviceState[systemState];
    powState.DeviceState = devState;

    powerContext = (PPOWER_COMPLETION_CONTEXT)
                   ExAllocatePool(NonPagedPool,
                                  sizeof(POWER_COMPLETION_CONTEXT));

    if(!powerContext) {

        IsoUsb_DbgPrint(1, ("Failed to alloc memory for powerContext\n"));

        ntStatus = STATUS_INSUFFICIENT_RESOURCES;
    }
    else {

        powerContext->DeviceObject = DeviceObject;
        powerContext->SIrp = SIrp;

        //
        // in win2k PoRequestPowerIrp can take fdo or pdo.
        //

        ntStatus = PoRequestPowerIrp(
                            deviceExtension->PhysicalDeviceObject,
                            irpStack->MinorFunction,
                            powState,
                            (PREQUEST_POWER_COMPLETE)DevPoCompletionRoutine,
                            powerContext,
                            NULL);
    }

    if(!NT_SUCCESS(ntStatus)) {

        if(powerContext) {

            ExFreePool(powerContext);
        }

        PoStartNextPowerIrp(SIrp);

        SIrp->IoStatus.Status = ntStatus;
        SIrp->IoStatus.Information = 0;

        IoCompleteRequest(SIrp, IO_NO_INCREMENT);

        IsoUsb_DbgPrint(3, ("SendDeviceIrp::"));
        IsoUsb_IoDecrement(deviceExtension);

    }

    IsoUsb_DbgPrint(3, ("SendDeviceIrp - ends\n"));
}


VOID
DevPoCompletionRoutine(
    IN PDEVICE_OBJECT DeviceObject,
    IN UCHAR MinorFunction,
    IN POWER_STATE PowerState,
    IN PVOID Context,
    IN PIO_STATUS_BLOCK IoStatus
    )
/*++

Routine Description:

    This is the PoRequest - completion routine for the device power irp.
    This routine is responsible for completing the system power irp,
    received as a context.

Arguments:

    DeviceObject - pointer to device object
    MinorFunction - minor function of the irp.
    PowerState - power state of the irp.
    Context - context passed to the completion routine.
    IoStatus - status of the device power irp.

Return Value:

    None

--*/
{
    PIRP                      sIrp;
    PDEVICE_EXTENSION         deviceExtension;
    PPOWER_COMPLETION_CONTEXT powerContext;

    //
    // initialize variables
    //

    powerContext = (PPOWER_COMPLETION_CONTEXT) Context;
    sIrp = powerContext->SIrp;
    deviceExtension = powerContext->DeviceObject->DeviceExtension;

    IsoUsb_DbgPrint(3, ("DevPoCompletionRoutine - begins\n"));

    //
    // copy the D-Irp status into S-Irp
    //

    sIrp->IoStatus.Status = IoStatus->Status;

    //
    // complete the system Irp
    //

    PoStartNextPowerIrp(sIrp);

    sIrp->IoStatus.Information = 0;

    IoCompleteRequest(sIrp, IO_NO_INCREMENT);

    //
    // cleanup
    //

    IsoUsb_DbgPrint(3, ("DevPoCompletionRoutine::"));
    IsoUsb_IoDecrement(deviceExtension);

    ExFreePool(powerContext);

    IsoUsb_DbgPrint(3, ("DevPoCompletionRoutine - ends\n"));

}

NTSTATUS
HandleDeviceSetPower(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp
    )
/*++

Routine Description:

    This routine services irps of minor type IRP_MN_SET_POWER
    for the device power state

Arguments:

    DeviceObject - pointer to device object
    Irp - I/O request packet sent by the power manager

Return Value:

    NT status value

--*/
{
    KIRQL              oldIrql;
    NTSTATUS           ntStatus;
    POWER_STATE        newState;
    PIO_STACK_LOCATION irpStack;
    PDEVICE_EXTENSION  deviceExtension;
    DEVICE_POWER_STATE newDevState,
                       oldDevState;

    IsoUsb_DbgPrint(3, ("HandleDeviceSetPower - begins\n"));

    //
    // initialize variables
    //

    deviceExtension = (PDEVICE_EXTENSION)DeviceObject->DeviceExtension;
    irpStack = IoGetCurrentIrpStackLocation(Irp);
    oldDevState = deviceExtension->DevPower;
    newState = irpStack->Parameters.Power.State;
    newDevState = newState.DeviceState;

    IsoUsb_DbgPrint(3, ("Set request for device power state D%X\n"
                        "Current device power state D%X\n",
                        newDevState - 1,
                        deviceExtension->DevPower - 1));

    if(newDevState < oldDevState) {

        //
        // adding power
        //
        IsoUsb_DbgPrint(3, ("Adding power to the device\n"));

        //
        // send the power IRP to the next driver in the stack
        //
        IoCopyCurrentIrpStackLocationToNext(Irp);

        IoSetCompletionRoutine(
                Irp,
                (PIO_COMPLETION_ROUTINE)FinishDevPoUpIrp,
                deviceExtension,
                TRUE,
                TRUE,
                TRUE);

        ntStatus = PoCallDriver(deviceExtension->TopOfStackDeviceObject, Irp);

    }
    else {

        IsoUsb_DbgPrint(3, ("Removing power or SetD0\n"));

        //
        // newDevState >= oldDevState
        //
        // hold I/O if transition from D0 -> DX (X = 1, 2, 3)
        // if transition from D1 or D2 to deeper sleep states,
        // I/O queue is already on hold.
        //

        if(PowerDeviceD0 == oldDevState && newDevState > oldDevState) {

            //
            // D0 -> DX transition
            //
            ntStatus = HoldIoRequests(DeviceObject, Irp);

            if(!NT_SUCCESS(ntStatus)) {

                PoStartNextPowerIrp(Irp);

                Irp->IoStatus.Status = ntStatus;
                Irp->IoStatus.Information = 0;

                IoCompleteRequest(Irp, IO_NO_INCREMENT);

                IsoUsb_DbgPrint(3, ("HandleDeviceSetPower::"));
                IsoUsb_IoDecrement(deviceExtension);

                return ntStatus;
            }
            else {

                goto HandleDeviceSetPower_Exit;
            }

        }
        else if(PowerDeviceD0 == oldDevState && PowerDeviceD0 == newDevState) {

            //
            // D0 -> D0
            // unblock the queue which may have been blocked processing
            // query irp
            //

            KeAcquireSpinLock(&deviceExtension->DevStateLock, &oldIrql);

            deviceExtension->QueueState = AllowRequests;

            KeReleaseSpinLock(&deviceExtension->DevStateLock, oldIrql);

            ProcessQueuedRequests(deviceExtension);
        }

        IoCopyCurrentIrpStackLocationToNext(Irp);

        IoSetCompletionRoutine(
                Irp,
                (PIO_COMPLETION_ROUTINE) FinishDevPoDnIrp,
                deviceExtension,
                TRUE,
                TRUE,
                TRUE);

        ntStatus = PoCallDriver(deviceExtension->TopOfStackDeviceObject, Irp);

        if(!NT_SUCCESS(ntStatus)) {

            IsoUsb_DbgPrint(1, ("Lower drivers failed a power Irp\n"));
        }

    }

HandleDeviceSetPower_Exit:

    IsoUsb_DbgPrint(3, ("HandleDeviceSetPower - ends\n"));

    return STATUS_PENDING;
}

NTSTATUS
FinishDevPoUpIrp(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp,
    IN PDEVICE_EXTENSION DeviceExtension
    )
/*++

Routine Description:

    completion routine for the device power UP irp with minor function
    IRP_MN_SET_POWER.

Arguments:

    DeviceObject - pointer to device object
    Irp - I/O request packet
    DeviceExtension - pointer to device extension

Return Value:

    NT status value

--*/
{
    NTSTATUS           ntStatus;

    //
    // initialize variables
    //

    ntStatus = Irp->IoStatus.Status;

    IsoUsb_DbgPrint(3, ("FinishDevPoUpIrp - begins\n"));

    if(Irp->PendingReturned) {

        IoMarkIrpPending(Irp);
    }

    if(!NT_SUCCESS(ntStatus)) {

        PoStartNextPowerIrp(Irp);

        IsoUsb_DbgPrint(3, ("FinishDevPoUpIrp::"));
        IsoUsb_IoDecrement(DeviceExtension);

        return STATUS_SUCCESS;
    }

    SetDeviceFunctional(DeviceObject, Irp, DeviceExtension);

    IsoUsb_DbgPrint(3, ("FinishDevPoUpIrp - ends\n"));

    return STATUS_MORE_PROCESSING_REQUIRED;
}

NTSTATUS
SetDeviceFunctional(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp,
    IN PDEVICE_EXTENSION DeviceExtension
    )
/*++

Routine Description:

    This routine processes queue of pending irps.

Arguments:

    DeviceObject - pointer to device object
    Irp - I/O request packet
    DeviceExtension - pointer to device extension

Return Value:

    NT status value

--*/
{
    KIRQL              oldIrql;
    NTSTATUS           ntStatus;
    POWER_STATE        newState;
    PIO_STACK_LOCATION irpStack;
    DEVICE_POWER_STATE newDevState,
                       oldDevState;

    //
    // initialize variables
    //

    ntStatus = Irp->IoStatus.Status;
    irpStack = IoGetCurrentIrpStackLocation(Irp);
    newState = irpStack->Parameters.Power.State;
    newDevState = newState.DeviceState;
    oldDevState = DeviceExtension->DevPower;

    IsoUsb_DbgPrint(3, ("SetDeviceFunctional - begins\n"));

    //
    // update the cached state
    //
    DeviceExtension->DevPower = newDevState;

    //
    // restore appropriate amount of state to our h/w
    // this driver does not implement partial context
    // save/restore.
    //

    PoSetPowerState(DeviceObject, DevicePowerState, newState);

    if(PowerDeviceD0 == newDevState) {

    //
    // empty existing queue of all pending irps.
    //

        KeAcquireSpinLock(&DeviceExtension->DevStateLock, &oldIrql);

        DeviceExtension->QueueState = AllowRequests;

        KeReleaseSpinLock(&DeviceExtension->DevStateLock, oldIrql);

        ProcessQueuedRequests(DeviceExtension);
    }

    PoStartNextPowerIrp(Irp);

    Irp->IoStatus.Status = STATUS_SUCCESS;
    Irp->IoStatus.Information = 0;

    IoCompleteRequest(Irp, IO_NO_INCREMENT);

    IsoUsb_DbgPrint(3, ("SetDeviceFunctional::"));
    IsoUsb_IoDecrement(DeviceExtension);

    IsoUsb_DbgPrint(3, ("SetDeviceFunctional - ends\n"));

    return STATUS_SUCCESS;
}

NTSTATUS
FinishDevPoDnIrp(
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp,
    IN PDEVICE_EXTENSION DeviceExtension
    )
/*++

Routine Description:

    This routine is the completion routine for device power DOWN irp.

Arguments:

    DeviceObject - pointer to device object
    Irp - I/O request packet
    DeviceExtension - pointer to device extension

Return Value:

    NT status value

--*/
{
    NTSTATUS           ntStatus;
    POWER_STATE        newState;
    PIO_STACK_LOCATION irpStack;

    //
    // initialize variables
    //
    ntStatus = Irp->IoStatus.Status;
    irpStack = IoGetCurrentIrpStackLocation(Irp);
    newState = irpStack->Parameters.Power.State;

    IsoUsb_DbgPrint(3, ("FinishDevPoDnIrp - begins\n"));

    if(NT_SUCCESS(ntStatus) && irpStack->MinorFunction == IRP_MN_SET_POWER) {

        //
        // update the cache;
        //

        IsoUsb_DbgPrint(3, ("updating cache..\n"));

        DeviceExtension->DevPower = newState.DeviceState;

        PoSetPowerState(DeviceObject, DevicePowerState, newState);
    }

    PoStartNextPowerIrp(Irp);