PURPOSE:To improve the storage efficiency of a buffer for tracing by gathering only effective information without storing the repetition of unnecessary data in the buffer for tracing. CONSTITUTION:Every time the branch instruction is executed, a comparator 17 compares the contents of a save address register 3 which are data to be traced with the contents of a trace copy register 6. When the comparison result of the comparator 17 shows a coincidence, '000' is set in a trace address low- order register 51. Consequently, the storage address of the buffer 4 for tracing is returned and next trace data is overwritten on trace data which is stored in this range. When the comparison result of the comparator 17 does not show the coincidence, the value of the save address register 3 is stored in the buffer 4 for tracing. Consequently, data is prevented from being stored repeatedly and the buffer for tracing can be used effectively.
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