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Developer’s Manual March, 2003 12-3
Intel
®
80200 Processor based on Intel
®
XScale
™
Microarchitecture
Performance Monitoring
12.3 Performance Count Registers (PMN0 - PMN1; CP14 -
Register 2 and 3, Respectively)
There are two 32-bit event counters; their format is shown in Table 12-2. The event counters are
reset to ‘0’ by the PMNC register or can be set to a predetermined value by directly writing to
them. When an event counter reaches its maximum value 0xFFFF,FFFF, the next event it needs to
count will cause it to roll over to zero and set the overflow flag (bit 8 or 9) in PMNC. An IRQ or
FIQ interrupt will be reported if it is enabled via bit 4 or 5 in the PMNC register.
12.3.1 Extending Count Duration Beyond 32 Bits
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 enables 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
).
Table 12-2. Performance Monitor Count Register (PMN0 and PMN1)
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
Event Counter
reset value: unpredictable
Bits Access Description
31:0 Read / Write
32-bit event counter - Reset to ‘0’ by PMNC register.
When an event counter reaches its maximum value
0xFFFF,FFFF, the next event it needs to count causes it
to roll over to zero and generate an IRQ or FIQ interrupt if
enabled.