MPC8540 datasheet(1090/1302 Pages) FREESCALE

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MPC8540 PowerQUICC III Integrated Host Processor Reference Manual, Rev. 1

19-12

Freescale Semiconductor

Performance Monitor

An illegal condition exists if the threshold value obtained from PMLCBn[THRESHOLD] and

PMLCBn[TBMULT] is less than two. Under these conditions the intent of threshold counting is

ambiguous.

Figure 19-9. Duration Threshold Event Sequence Timing Diagram

19.4.4 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 19-10, are

dedicated to specific registers.

Note that the chaining overflow event occurs when the counter reaches its maximum value and

wraps, not when the register’s msb is set. For this overflow to occur, PMLCAn[CE] should be

cleared to avoid signalling an interrupt when the counter’s most-significant bit is set. Note that

several cycles may be required for the chained counters to reflect the true count because of the

internal delay between when an overflow occurs and a counter increments.

19.4.5 Triggering

Triggering allows one counter to start or stop counting on the change of another counter or on the

overflow of another counter. More specifically, if PMC1 is set to start or stop counting as a result

of a change or overflow in counter PMC2, then counter PMC2 must be identified in the local

thresh_value

thresh_start

thresh_stop

thresh_counter

thresh_exceeded

PMLCBn[THRESHOLD]

PMLCBn[TBMULT]

perfmon_counter

3456

8910

1 For this example a threshold value of three indicates that the user wishes to count the

number of times a particular event lasts three cycles or longer.

MPC8540 Datasheet(PDF) 1090 Page - Freescale Semiconductor, Inc