IPortDMus::Notify method (dmusicks.h)

Article
10/21/2021

The Notify method should be called from the miniport driver's interrupt service routine (ISR) when a hardware interrupt has occurred. This call requests that the port driver call the miniport driver back with a deferred procedure call (DPC) while the miniport driver handles the interrupt.

Syntax

void Notify(
  [in, optional] PSERVICEGROUP ServiceGroup
);

Parameters

[in, optional] ServiceGroup

Pointer to an IServiceGroup object. This parameter is optional and can be specified as NULL. For more information, see the following Remarks section.

Return value

None

Remarks

The Notify method sends notification to the miniport driver's service group:

If the pServiceGroup parameter is non-NULL, the Notify method calls the RequestService method on the IServiceGroup object that this parameter points to.
If pServiceGroup is NULL:
- The Notify method calls the RequestService method on the miniport driver's IServiceGroup object. This is the IServiceGroup object that the miniport driver output during the IMiniportDMus::Init call. The miniport driver also might have registered this object early (that is, earlier than the return from Init) by calling IPortDMus::RegisterServiceGroup.
- The Notify method also calls the RequestService method on the IServiceGroup object belonging to each of the miniport driver's streams. This is the IServiceGroup object that the IMiniportDMus::NewStream method outputs.

The miniport driver typically calls Notify to notify the port driver that the audio device has generated a hardware interrupt. When an interrupt signals, for example, that some register needs to be read, the miniport driver's ISR cannot access the MXF (MIDI transform filter) graph at the elevated IRQL. Instead, the miniport driver can store the input data (a byte of MIDI data, for example) from the register, call Notify, and wait for the port driver to get back to it with a DPC.

When the miniport driver's ISR calls Notify, the port driver receives the notification at the elevated hardware interrupt IRQL and puts a DPC on the queue. When IRQL drops to the DISPATCH_LEVEL, the port driver's DPC fires and services the miniport driver.

Within the DPC, the port driver calls IMXF::PutMessage on the miniport driver's input stream with a parameter of NULL to signify that the miniport driver can now put the previously stored MIDI message into the MXF graph because the IRQL has dropped back to DISPATCH_LEVEL.

This method is vital for accurate timing. Most miniports will call this method in response to a notification interrupt after having cleared the interrupt source. Although the miniport driver is free to use other methods for determining when to call this method, precise timing is important and should be maintained.

When an adapter driver installs an ISR, it submits a ServiceContext parameter along with the ISR's entry point (for details, see Providing ISR Context Information). When the interrupt occurs, the operating system calls the ISR and passes ServiceContext as a call parameter to the ISR. Although the meaning of the ServiceContext parameter is known only to the driver developer, it is typically a pointer to the miniport object. The ISR uses this pointer to access information about the miniport object.

The pServiceGroup parameter follows the reference-counting conventions for COM objects.

Requirements

Requirement	Value
Target Platform	Desktop
Header	dmusicks.h (include Dmusicks.h)
IRQL	Any level