Patent ID: 7221650

Claim:
In a system in which a first module issues a plurality of first messages to a second module that responds by issuing a plurality of second messages back to the first module, a method of checking whether one or more of the first or second messages have been lost or gained, the method comprising the steps of: providing a request counter at the first module; incrementing the request counter in response to each first message issued by the first module; decrementing the request counter in response to each second message received at the first module; providing a capture register at the first module; providing a request accumulator at the second module; incrementing the request accumulator in response to each first message received at the second module; decrementing the request accumulator in response to each second message issued by the second module; providing a capture register at the second module; issuing a marker message from the first module to the second module; storing the current value of the request counter in the capture register of the first module upon issuance of the marker message; upon receiving the marker message at the second module, copying the current value of the request accumulator into the capture register of the second module; returning the marker message back to the first module; decrementing the capture register of the first module in response to each second message received at the first module from the time the marker message is issued until the marker message is returned to the first module; and comparing the contents of the capture registers at the first and second modules.