Performance Monitor
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
25-71
Note:
Using PMLCAn[FC] resets only the specified counter. Performance monitor registers
can be configured through reads or writes while the counters are frozen as long as
freeze bits are not cleared by the register accesses.
25.3.1.3 Threshold Events
The quantity threshold event sequences the performance monitor counter is only incremented
when the specified threshold event exceeds the threshold value. Threshold event is generally used
to monitor the usage of buffers and queues. For example, the usage of a specific queue can be
characterized by measuring the amount of time the queue is completely full or partially full. For
this example the threshold field would be used to specify how many entries are required to be
valid in the queue for that event to be counted.A timing diagram for quantity threshold event
counting is shown in Figure 25-17.
25.3.1.4 Chaining
By configuring one counter to increment each time another counter overflows, several counters
can be chained together to provide event counts larger than 32 bits. Each counter in a chain adds
32 bits to the maximum count. The register chaining sequence is not arbitrary and is specified
indirectly by selecting the register overflow event to be counted. Selecting an event has the effect
of selecting a source register because all available chaining events, as shown in Table 25-39, are
dedicated to specific registers.
Note:
The chaining overflow event occurs when the counter reaches its maximum value and
wraps, not when the register msb is set. For this overflow to occur, PMLCAn[CE]
should be cleared to avoid signalling an interrupt when the counter most significant bit
Figure 25-17. Quantity Threshold Event Sequence Timing Diagram
1
2
3
4
5
6
7
8
9
10
11
12
2
2
PMLCBn[THRESHOLD]
thresh_value
0
1
2
3
4
5
6
0_entries_in_queue
1_entry_in_queue
2_entries_in_queue
3_entries_in_queue
4_entries_in_queue
counter_increment
perfmon_counter
Note: For this example a threshold value of two indicates the user wishes to count the
number of cycles. There are at least two valid entries in a particular queue.
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