Synchronizing data tracks using global force windows and track sync counters in a multitrack tape device

摘要

A method and apparatus which first calculates track to track skew in a tape device and then uses the results of that calculation to adjust the windows for detection of sync and resync characters. The system makes use of global circuitry which adjusts the sync and resync windows for all tracks based upon the skew calculation. In the case of the windows used for detecting resyncs, when skew is determined to be large, the global resync window must span a larger time period to account for the skew in detecting resync marks. Conversely, when there is little or no skew present, the windows for resync detection can be narrowed. Normally, the track logic utilizes its own local windows to detect resyncs. If a track misses a resync, however, it must use the global resync window to determine the next resync location. Once the tracks are resynchronized, control can return to local track circuitry to maintain synchronization. In the case of force windows used for detecting the syncs after a resync alignment burst, the skew calculation is used to determine the correct sync location for each particular track. Further, data alignment is maintained in the multitrack environment through the use of a deinterleaving circuit which receives misalignment indications and, in response, makes address corrections to data bytes and pointer bytes.