| 摘要 |
A data processing apparatus and method for measuring a value of a predetermined property of transactions are provided. The data processing apparatus has initiator circuitry for initiating transactions, recipient circuitry for handling each transaction initiator by the initiator circuitry, and a communication path interconnecting the initiator circuitry and the recipient circuitry via which the transactions are propagated between the initiator circuitry and the recipient circuitry. Measurement circuitry is coupled to the communication path for measuring a value of a predetermined property of the transactions, such as the latency of those transactions. The measurement circuitry has active transaction count circuitry for maintaining an indication of the number of transactions in progress, and accumulator circuitry for maintaining an accumulator value which is increased dependent on the number of transactions in progress. Further, a value register is provided for maintaining an estimate of the value of the predetermined property. Each time a transaction in progress reaches a predetermined point, for example a transaction end point, the accumulator value is decreased dependent on the estimate currently stored in the value register, and further the estimate stored in the value register is updated dependent on the accumulator value. Via this feedback mechanism, the estimate stored in the value register quickly settles to the actual value of the predetermined property being measured, and accordingly such measurement circuitry provides a simple, low cost and flexible mechanism for measuring the value of a predetermined property of transactions.
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