When events are traced, the timing stream is used to associate events with instructions and indicate pipeline advances precluding the recording of stall cycles. Additional information is needed in the trace stream to identify an overlay whose execution of code is in a system where overlays or a memory management unit are used. In the case of PC trace, additional information is added when the memory system contents is changed. Information describing the configuration change is inserted into the export streams by placing this information in a message buffer. As long as a message word is available for output, it becomes the next export word as the output of message words is continuous.