Intel IXP42X User Manual

Intel

®

 IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor

DM

September 2006

138

Order Number: 252480-006US

The following are a few notes about controlling the performance monitoring 

mechanism:

• An interrupt request will be generated when a counter’s overflow flag is set and its 

associated interrupt enable bit is set in INTEN. The interrupt request will remain 

asserted until software clears the overflow flag by writing a one to the flag that is 

set. (Note that the product specific interrupt unit and the CPSR must have enabled 

the interrupt in order for software to receive it.) The interrupt request can also be 

deasserted by clearing the corresponding interrupt enable bit. Disabling the facility 

(PMNC.E) doesn’t deassert the interrupt request. 

• The counters continue to record events even after they overflow. 
• To change an event for a performance counter, first disable the facility (PMNC.E) 

and then modify EVTSEL. Not doing so will cause unpredictable results.

• To increase the monitoring duration, software can extend the count duration 

beyond 32 bits by counting the number of overflow interrupts each 32-bit counter 

generates. This can be done in the interrupt service routine (ISR) where an 

increment to some memory location every time the interrupt occurs will enable 

longer durations of performance monitoring. This does intrude upon program 

execution but is negligible, since the ISR execution time is in the order of tens of 

cycles compared to the number of cycles it took to generate an overflow interrupt 

(2

32

). 

• Power can be saved by selecting event 0xFF for any unused event counter. This 

only applies when other event counters are in use. When the performance monitor 

is not used at all (PMNC.E = 0x0), hardware ensures minimal power consumption. 

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9

8

7

6

5

4

3

2

1

0

31:24

Read / Write

Event Count 3 (evtCount3) - 
Identifies the source of events that PMN3 counts. See 

 for a description of the values this field may 

contain.

23:16

Read / Write

Event Count 2 (evtCount2) - 
Identifies the source of events that PMN2 counts. See 

 for a description of the values this field may 

contain.

15:8

Read / Write

Event Count 1 (evtCount1) - 
Identifies the source of events that PMN1 counts. See 

 for a description of the values this field may 

contain.

7:0

Read / Write

Event Count 0 (evtCount0) - 
Identifies the source of events that PMN0 counts. See 

 for a description of the values this field may 

contain.