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ST20-GP6

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14.6.2 Software solutions

If the user wishes to break on the

nth occurrence of a given instruction using a counter in the DCU,

then there is no problem associated with abortable instructions because the counter is adjusted on

the completion of the instruction, not the start of the instruction. More speciﬁcally, the counter is

adjusted when the CPU commits to executing the instruction; this may be at the completion of an

abortable instruction, or it may be at an interrupt point in the middle of an interruptible instruction.

In the more complex example, the user wishes to break on the nth occurrence of a given instruction

in a given thread. In this case, a hardware break is set on the given instruction, and the breakpoint

trap handler contains just enough code to distinguish the desired thread and decrement a counter

in software. Of course, inserting the breakpoint makes the instruction appear to be abortable and

the count is not reliable. However, if a pair of break points are used, and counting only takes place

when the desired thread moves from the ﬁrst to the second breakpoint, then a reliable count can be

established.

ST20-GP6 데이터시트(PDF) 81 Page - STMicroelectronics