Intel IXP400 manual Aqm

Intel® IXP400 Software

Access-Layer Components: Queue Manager (IxQMgr) API

5. The ISR invokes the dispatcher.

Note: In the context of an interrupt, the dispatcher can also be invoked through a timer-based mechanism.

6.The IxQMgr reads the status flag.

7.The IxQMgr access-layer component calls the registered notification.

8.The client gets the buffer pointer on the Rx queue from the access-layer through the callback. The access-layer, in turn, accesses the Rx queue through the IxQMgr access-layer component. The IxQMgr accesses the AQM hardware.

Following this, the Intel XScale core may allocate a free buffer from the memory pool to the RxFree queue for the next incoming packet from the NPE.

Figure 90. Dispatcher in Context of an Interrupt

	1			8	Get	the
		Register callback			Queue
	User	Access-		QMgr		5	ISR in OS
		layer
	Callback			Component			(or) Timer
		Component	7
		Get Queue-Status		6
	Queue Status Bus	AQM					Hardware
					Status
	to NPEs	Status
NPE					Flags
		Flags
2	Low Group		High Group
	0	31 32				63	4
			Interrupt High to Intel
	Interrupt Low to Intel			XScale® Core			Intel XScale®
		®
	XScale Core					3	Core Interrupt
							Controller
							B3805 01

Figure 91 shows the sequence of events that occurs when a dispatcher is ran in the context of a polling mechanism.

At the start of the dispatcher a call is made to read the status of the status flag to check if the queue watermark threshold has been crossed. It then immediately clears the status flag. In case of livelock prevention feature, the status flag is not cleared immediately because of the sticky interrupt implementation.

1.The user registers a callback function with the access-layer component (for example, EthAcc). The dispatcher invokes callback in the access-layer component, and the access-layer component then invokes the user callback.

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	271