Tracing speculatively executed instructions

A trace unit according to claim 29 said trace control data comprising a traced-interesting value, said traced-interesting value being set for a group of instructions in response to a trace element being output for said group of instructions and being clear for a group of instructions where no trace element is output for said group of instructions, wherein said trace circuitry is configured to determine said information regarding said difference in dependence upon said traced-interesting value.

A method for generating items of trace data indicative of processing activities of at least one processor executing at least one stream of instructions, said at least one stream of instructions comprising a plurality of groups of instructions, said at least one processor executing at least some of said instructions speculatively, said method comprising the steps of:

• monitoring a behaviour of said at least one processor using trace circuitry controlled by trace control data;
• updating a data store to store at least some of said trace control data associated with one of said groups of instructions that has been executed;
• in response to detecting a cancelled group of instructions from said plurality of groups of instructions, wherein said cancelled group of instructions has been speculatively executed and cancelled by said at least one processor, retrieving at least some of said trace control data stored in said data store and controlling said trace circuitry with said retrieved trace control data.