1. Apparatus for processing data, said apparatus comprising: (i) a data processing circuit operable over a sequence of processing cycles to perform data processing operations in response to program instructions; and (ii) a tracing circuit operable to generate instruction trace data indicative of operation of said data processing circuit in response to said program instructions; (iii) wherein said instruction trace data includes at least one instruction trace word of a predetermined length encoding a sequence of trace events resulting from processing performed on consecutive processing cycles by said data processing circuit, said sequence of trace events including: (iv) at least one trace event corresponding to execution of a program instruction by said data processing circuit; and (v) at least one trace event corresponding to other than execution of a program instruction by said data processing circuit.