Selecting highest reliability sync mark in a sync mark window of a spiral servo track crossing
View Patent ↗A method is disclosed for demodulating a spiral servo track recorded on a disk of a disk drive. The spiral servo track comprises a high frequency signal interrupted by a sync mark at a sync mark interval. A demodulation window is enabled relative to a spiral servo track crossing, and a plurality of sync marks are detected in a sync mark window of the demodulation window. A reliability metric is generated for each of the detected sync marks, wherein the reliability metrics are evaluated to select one of the detected sync marks. A clock is synchronized in response to the selected sync mark.
1. A method of demodulating a spiral servo track recorded on a disk, the spiral servo track comprising a high frequency signal interrupted by a sync mark at a sync mark interval, the method comprising:
enabling a demodulation window relative to a spiral servo track crossing;
searching for a sync mark within a sync mark window of the demodulation window, wherein the sync mark window represents a time within the demodulation window that the sync mark is expected to occur;
detecting a plurality of sync marks in the sync mark window;
generating a reliability metric for each of the detected sync marks;
evaluating the reliability metrics to select one of the detected sync marks; and
synchronizing a clock in response to the selected sync mark.
2. The method as recited in claim 1 , wherein the clock comprises a servo write clock for writing concentric servo sectors to the disk.
3. The method as recited in claim 1 , wherein each reliability metric corresponds to a signal amplitude of the corresponding detected sync mark.
4. The method as recited in claim 3 , wherein each reliability metric further corresponds to a correlation value of the corresponding detected sync mark.
5. The method as recited in claim 1 , wherein each reliability metric corresponds to a correlation value of the corresponding detected sync mark.
6. The method as recited in claim 1 , wherein the detected sync mark having the highest signal amplitude is the selected sync mark.
7. The method as recited in claim 1 , wherein the demodulation window comprises a plurality of sync mark windows corresponding to a plurality of expected sync marks within the spiral servo track crossing.
8. The method as recited in claim 7 , wherein a plurality of sync marks may be detected within any one of the sync mark windows.
9. A disk drive comprising:
a disk comprising a spiral servo track, the spiral servo track comprising a high frequency signal interrupted by a sync mark at a sync mark interval;
a head actuated over the disk; and
control circuitry operable to:
enable a demodulation window relative to a spiral servo track crossing;
search for a sync mark within a sync mark window of the demodulation window, wherein the sync mark window represents a time within the demodulation window that the sync mark is expected to occur;
detect a plurality of sync marks in the sync mark window;
generate a reliability metric for each of the detected sync marks;
evaluate the reliability metrics to select one of the detected sync marks; and
synchronize a clock in response to the selected sync mark.
10. The disk drive as recited in claim 9 , wherein the clock comprises a servo write clock for writing concentric servo sectors to the disk.
11. The disk drive as recited in claim 9 , wherein each reliability metric corresponds to a signal amplitude of the corresponding detected sync mark.
12. The disk drive as recited in claim 11 , wherein each reliability metric further corresponds to a correlation value of the corresponding detected sync mark.
13. The disk drive as recited in claim 9 , wherein each reliability metric corresponds to a correlation value of the corresponding detected sync mark.
14. The disk drive as recited in claim 9 , wherein the detected sync mark having the highest signal amplitude is the selected sync mark.
15. The disk drive as recited in claim 9 , wherein the demodulation window comprises a plurality of sync mark windows corresponding to a plurality of expected sync marks within the spiral servo track crossing.
16. The disk drive as recited in claim 15 , wherein a plurality of sync marks may be detected within any one of the sync mark windows.