Method and apparatus for improved timing for trace synchronization

A data processing apparatus having one or more trace data sources is provided in which the trace data sources operate to generate respective streams of trace data. At least one of said trace data sources comprises a trace data generator responsive to activity in monitored circuitry to generate trace data representing said activity. A synchronization marker generator is coupled to the trace data generator and operates to generate a synchronization marker and insert the synchronization marker into the trace data stream. The synchronization marker identifies a synchronization position in the trace data stream. A controller is coupled to the synchronization marker generator, and operates to initiate the synchronization marker generator to generate and insert a synchronization marker into the trace data stream. The controller controls initiation in dependence on behaviour of the data processing apparatus downstream of the trace data generator with respect to trace data flow. In this way, the downstream behaviour of the data processing apparatus can be made to influence the rate and timing of insertion of synchronization markers into a trace data stream, thereby reducing the likelihood of the volume of trace data resulting in an overflow condition in the downstream circuitry.