GPS-based time stamp system

A time stamp validation system, comprising:

• a GPS receiver operable to receive a GPS time signal representing GPS time data;
• a local clock operable to provide local time data;
• wherein the local clock is initialized by, and disciplined by, the GPS time signal to provide time stamp data, unless a compromise of the GPS signal is detected;
• an error detector operable to determine a current time difference between the GPS time data and the local time data, thereby determining an error value;
• a threshold comparator operable to determine if the time difference exceeds a predetermined threshold;
• a delay and reject process operable to determine whether the GPS time data is to be accepted;
• wherein the delay and reject process operates on past GPS time data and past local time data;
• a proportional integral (PI) controller operable to output discipline values to discipline the local clock in either of two ways:
• if the GPS time is accepted, to provide a current discipline value based on the error value, or if the GPS time is not accepted, to provide a prior discipline value based on the most recent prior output of the PI controller;
• and
• a main controller operable to generate time stamps, using current discipline values if the GPS time is accepted, and if the GPS time is not accepted, using the same prior discipline value without reference to any external time source until the GPS time is verified;
• wherein the delay and reject process operates on past GPS time data and past local time data, such that main controller applies discipline values to current local time data.