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IXP400 Software
Access-Layer Components: Queue Manager (IxQMgr) API
Programmer’s Guide IXP400 Software Version 2.0 April 2005
Document Number: 252539, Revision: 007 273
To use livelock prevention, only one queue can be set as type periodic. One or more queues may be
set as type sporadic using the ixQMgrCallbackTypeSet() function. By default, all the other queues
that are not set to be in either a periodic or a sporadic mode are set in
IX_QMGR_TYPE_REALTIME_OTHER mode. The IX_QMGR_TYPE_REALTIME_OTHER
represents the default behavior of the callback function associated with respective queues when the
livelock prevention feature is not in use. In a Livelock implimentation, these “other” queues will
not have their interrupts disabled during the servicing of the periodic queue.
The ixQMgrCallbackTypeSet() function should be used to assign
IX_QMGR_TYPE_REALTIME_PERIODIC to one queue and
IX_QMGR_TYPE_REALTIME_SPORADIC to queue(s) by passing a Queue-ID along with the
desired queue type.
Livelock prevention is disabled by default. In order to enable the livelock option the
IX_FEATURECTRL_ORIGB0_DISPATCHER must be disabled using the
ixFeatureCtrlSwConfigurationWrite() function before the ixQMgrInit() and
ixQMgrDispatcherLoopGet() functions are called.
Queue assignments are located at ixp400_xscale_sw\src\include\IxQueueAssignments.h. If
Ethernet QoS features are used, the Rx Priority queues are assigned in
ixp400_xscale_sw\src\include\IxEthDBQoS.h. Queue type assignments may be checked with the
ixQMgrCallbackTypeGet() function.
When ixQMgrDispatcherLoopRunB0LLP() reads the interrupt register and sees that a periodic
queue is to be serviced, all queues that are set to be sporadic have their notification disabled. This
prevents sporadic queues from generating interrupts, which may stall a task resulting from the
periodic queue callback (periodic task). The ixQMgrPeriodicDone() function should be called after
the periodic task is completed to ensure that sporadic queues are re-enabled.
Note: Because livelock prevention enables and disables notifications for queues set as sporadic, users
should not enable and disable sporadic queues notifications other than at startup / shutdown.
Note: Livelock prevention operates on lower interrupt register queues only. (lower queue group 0-31).
Note: The Livelock dispatcher does not work on A-0 stepping versions of the IXP42X product line.
The following is an example sequence to show how livelock would be used is to set the HSS queue
to periodic and the Eth Rx queue to sporadic using the ixQMgrCallbackTypeSet() function. When
codec processing (the periodic task) as a result of a HSS callback is finished, the
ixQMgrPeriodicDone() function is called and Eth Rx is then serviced. This will ensure that any
codec processing that is done as a result of HSS notifications is not interrupted by a burst in Eth
Rx.
• Use ixFeatureCtrlSwConfigurationWrite() to disable
IX_FEATURECTRL_ORIGB0_DISPATCHER.
• Initialize the Queue Manager by using ixQMgrInit( ).
• Make a call to ixQMgrDispatcherLoopGet() to get the appropriate dispatcher function for
livelock functionality.
• Initialize access-layer components, register the callback functions.