Method and system for frequency synchronization

An apparatus for synchronizing the frequency of a clock in a slave device which is communicatively coupled to a master device, the clock comprising:

• an oscillator;
• and
• a pulse counter counting pulses from said oscillator,
• the apparatus comprising:
• a receiver receiving messages from said master device;
• a time-stamp extraction device for extracting time-stamps applied to said messages by said master device;
• and
• a detector for detecting a difference between a time-stamp extracted from said messages and an output of said pulse counter and generating an error signal based on said difference,
• wherein:
• the receiver receives a first message from said master device having a first time-stamp which is a time-stamp of said master clock indicating the time of sending of said first message and initializes said pulse counter on receipt of said first message;
• the time-stamp extraction device extracts said first time-stamp from said first message;
• the receiver receives a second message from said master device having a second time-stamp, which is a time-stamp of said master clock indicating the time of sending said second message, and the detector reads the value of said pulse counter at the time of receipt of said second message;
• the time-stamp extraction device extracts said second time-stamp from said second message;
• the detector determines said error signal representative of the difference between said value of the counter and the difference between said first and second time-stamps;
• and
• said oscillator adjusts its frequency of oscillation based on said error signal.

A method of synchronizing the frequency of a slave clock in a slave device to a master clock in a master device, the method including the steps of:

• a) receiving in the slave device a first message from said master device having a first time-stamp, which is an approximate time-stamp of said master clock indicating the time of sending of said first message;
• b) extracting said first time-stamp from said first message and initializing a counter in the slave device which counts an output of said slave clock;
• c) receiving in the slave device a second message from said master device having a second time-stamp, which is a time-stamp of said master clock indicating the precise time of sending of said first message;
• d) extracting said second time-stamp from said second message;
• e) calculating a correction value, representative of the difference between the value of the first time-stamp and the value of the second time-stamp;
• f) receiving in the slave device a third message from said master device, and reading the value of said counter at the time of receipt of said third message;
• g) receiving in the slave device a fourth message from said master device having a third time-stamp, which is a time-stamp of said master clock indicating the precise time of sending said third message;
• h) extracting said third time-stamp from said fourth message;
• i) calculating an error signal, which is representative of the difference between the value of said counter, as read in step f) and said third time-stamp, adjusted using said correction value;
• and
• j) adjusting the frequency of said slave clock based on said error signal.

An apparatus for synchronizing the frequency of a clock in a slave device which is communicatively coupled to a master device, the clock comprising:

• an oscillator;
• and
• a pulse counter counting pulses from said oscillator,
• the apparatus comprising:
• a receiver receiving messages from said master device;
• a time-stamp extraction device for extracting time-stamps applied to said messages by said master device;
• a calculator for calculating a difference between time-stamps;
• and
• a detector for detecting a difference between a time-stamp extracted from said messages and an output of said pulse counter and generating an error signal based on said difference,
• wherein:
• the receiver receives a first message from said master device having a first time-stamp, which is a time-stamp of said master clock indicating the approximate time of sending of said first message;
• the time-stamp extraction device extracts said first time-stamp from said first message and initializes said pulse counter on receipt of said first message;
• the receiver receives a second message from said master device having a second time-stamp, which is a time-stamp of said master clock indicating the precise time of sending of said first message;
• the time-stamp extraction device extracts said second time-stamp from said second message;
• the calculator calculates a correction value, representative of the difference between the value of the first time-stamp and the value of the second time-stamp;
• the receiver receives a third message from said master device, and the detector reads the value of said counter at the time of receipt of said third message;
• the receiver receives a fourth message from said master device having a third time-stamp, which is a time-stamp of said master clock indicating the precise time of sending said third message;
• the time-stamp extraction device extracts said third time-stamp from said fourth message;
• the detector calculates an error signal, which is representative of the difference between the value of the counter, read by the detector, and said third time-stamp, adjusted using said correction value;
• and
• said oscillator adjusts its frequency of oscillation based on said error signal.