Systems and methods are disclosed for precisely determining the delay between data being received at the pins of a circuit and being processed by gearbox circuitry, to being processed by a time-stamp unit of the circuit. In an exemplary embodiment, the gearbox circuitry may output a data valid signal which may be monitored by the time-stamp unit. By monitoring the data valid signal, the time-stamp unit may synchronize a local state machine with the internal state of the gearbox circuitry and thus determine the total delay through the combined processing circuitry with high accuracy.