Maintenance of data synchronization across large gaps in a data stream

Apparatus for synchronizing a data read mechanism with frame units read by the data read mechanism, the apparatus comprising:

• an input receiving a datastream for reading;
• circuitry for selecting a sync pattern for detection;
• first and second sync detection filters for detecting a sync pattern sequence from the datastream, using a window size during which a subsequent sync pattern would be detected should the selected sync pattern continue, and after detecting the sync pattern sequence from the datastream, attempting to detect the subsequent sync pattern;
• and
• a selection circuit responding to a predetermined failure of detection of the subsequent sync pattern fails a predetermined number of sequential times, the selection circuit alternately using the first and second sync detection filters in order to detect a new sync pattern, wherein if one of the first and second sync detection filters detects a sync pattern, using said one of the first and second sync detection filters to attempt to detect subsequent sync patterns, and if detection of the subsequent sync pattern fails the predetermined number of sequential times, using the other one of the first and second sync detection filters to detect a subsequent new sync pattern.

Apparatus for synchronizing a data read mechanism with frame units read by the data read mechanism, the apparatus comprising:

• a sync detect logic circuit comprising circuitry for tracking a sync pattern in a bitstream of data read by the data read mechanism, comprising a state machine and logic to handle sync detection when at least one large jump or gap is present in the data stream, and providing a sync output signal in response to the tracked sync pattern;
• an additional sync detect logic circuit capable of sync detection, the additional logic circuit detecting the sync pattern when the sync detect logic circuit fails to track said sync pattern, and providing a sync output signal in response to the tracked sync pattern;
• and
• a master state machine to select which of the logic circuits is used to provide a sync output signal.

A method for synchronizing a data read mechanism with frame units read by the data read mechanism, the method comprising:

• providing a requirement for a sync jump comprising a process of failure to detect a sync pattern within a predefined window of variation from a predetermined number of data bits;
• using a state machine to detect a new sync pattern when the sync jump is required;
• determining which direction to effect a sync jump;
• and
• effecting the sync jump.