186
Development Tools User’s Guide
Intel
®
IXP2400/IXP2800 Network Processors
Performance Monitoring Unit
3.4.3.3
Sampling Considerations
The PMU logic in the IXP2400 and IXP2800 causes the counting of the number of occurrences of
2X events (see
) to behave in a non-intuitive fashion. In particular, if the event lasts only
one cycle, then it is counted as one occurrence. If the event lasts for two or more cycles, it is
counted as two occurrences. Depending on when the event occurs, the PMU counter may
increment twice in a row, or it may count by two in a single cycle.
If a PMU counter is reset at the same time that the event that it is counting is active, it will reset to
a non-zero value. Conceptually, it is as if the counter was reset to zero and then it counted the
event.
3.4.4
Event Selection Dialog Box
The Event Selection dialog box (see
) is used to specify macro events. It is presented by
depressing the
Events…
button on the TBS and RBS property pages.
Note:
When selecting events for the Monitor macro, one can check multiple events. In this case, you end
up with several monitor macros, one for each selected event. For other times when you are
selecting an event, only one event should be checked. If more than one is checked, the first event
checked is used.
Selected
Threshold Event
Event that causes the first counter to increment.
Duration
Specifies whether the first counter is incremented once for each occurrence of the
specified event or one for each clock cycle for which the event is active.
Buttons
Clear
Clear
will clear the currently selected events.
Events
Open the Event Selection dialog box (see
OK
Accept the current selections and close the Sampling Macros dialog box.
Cancel
Close the Sampling Macros dialog box and cancel all changes.
Table 7. Threshold Sampling Macro Dialog Box
Type
Description