Techniques and mechanisms to modify packet information in support of on-chip test functionality. In an embodiment, an integrated circuit (IC) chip includes a protocol stack to receive and process packetized information—e.g., where the processing of at least one isochronous timestamp packet (ITP) includes circuitry of the protocol stack replacing non-deterministic data of the ITP with substitute information. A deterministic nature of the substitute information enables the subsequent generation of corresponding signature information which can be used in an evaluation of circuit performance. In another embodiment, the ITP packet is modified at a transaction layer of the protocol stack, and the signature information is determined with an accumulator circuit which is part of another layer of the protocol stack.