Disk-locked loop in self-servo-write using spiral sync-mark detection

1. A method for writing servo wedge code to a disk, comprising:

determining a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met, using a processor to:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors;

after the lock criterion is met, writing servo wedge code to the disk; and

in the event one of the plurality of wedge frequency errors exceeds a maximum wedge frequency error, setting that wedge frequency error to 0.

2. A method as recited in claim 1 , wherein for each wedge-to-wedge time interval, the clock is adjusted based at least in part on the wedge frequency error associated with that wedge-to-wedge time interval.

3. A method as recited in claim 1 , wherein the wedge-to-wedge time interval is determined based at least in part on the total number of servo wedges to be written.

4. A method as recited in claim 1 , wherein computing a wedge frequency error includes:

detecting a known mark in a spiral segment in an intersection of a spiral waveform with a track on a disk;

determining a current detection time indication associated with a time when the known mark was detected; and

computing the wedge frequency error based at least in part on the current detection time indication and a previous detection time indication.

5. A method as recited in claim 4 , wherein the previous detection time indication is associated with the time of detection of the same known mark in a previous revolution.

6. A method as recited in claim 4 , wherein computing the wedge frequency error includes taking the difference between a current detection time indication and a previous detection time indication.

7. A method as recited in claim 4 , further including determining whether the known mark needs to be changed due to a servo wedge being written over the known mark and in the event that the known mark needs to be changed, changing the known mark.

8. A method as recited in claim 4 , wherein there are two intersections per wedge-to-wedge time interval.

9. A method as recited in claim 1 , wherein the lock criterion is met when, for each wedge-to-wedge time interval, the absolute value of the corresponding wedge frequency error is within a wedge frequency error limit for a predefined number of consecutive disk revolutions.

10. A method as recited in claim 1 , wherein after the lock criterion is met, computing a wedge frequency error is performed differently from before the lock criterion is met.

11. A method as recited in claim 1 , wherein the lock criterion is met if each of the plurality of wedge frequency errors is less than a wedge frequency error limit for a certain number of disk revolutions.

12. A method as recited in claim 11 , wherein after the lock criterion is met, the adjustable clock resets at the same circumferential location in each wedge-to-wedge time interval on every disk revolution, within a wedge frequency error limit.

13. A method as recited in claim 1 , wherein the clock is adjusted based at least in part on an output of a loop filter that takes the wedge frequency error as input.

14. A method as recited in claim 13 , wherein the loop filter includes an accumulator configured to sum two or more of the plurality of wedge frequency errors.

15. A method for writing servo wedge code to a disk, comprising:

determining a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met, using a processor to:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors; and

after the lock criterion is met, writing servo wedge code to the disk, wherein after the lock criterion is met, the wedge frequency error is computed based at least in part on one or more of the following:

a target detection time indication defined as the value of the time stamp when changing to the lock state; or

a target detection time indication that stays the same during the lock state.

16. A method for writing servo wedge code to a disk, comprising:

determining a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met, using a processor to:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors; and

after the lock criterion is met, writing servo wedge code to the disk, wherein:

the lock criterion is met if each of the plurality of wedge frequency errors is less than a wedge frequency error limit for a certain number of disk revolutions; and

the adjustable clock resets N wedge times per disk revolution, where N wedge is the number of wedges on the disk.

17. A system for writing servo wedge code to a disk, comprising:

a processor configured to:

determine a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors;

after the lock criterion is met, write servo wedge code to the disk; and

in the event one of the plurality of wedge frequency errors exceeds a maximum wedge frequency error, setting that wedge frequency error to 0; and

a communication interface coupled to the processor.

18. The system recited in claim 17 , wherein the processor is configured to compute a wedge frequency error at least in part by:

detecting a known mark in a spiral segment in an intersection of a spiral waveform with a track on a disk;

determining a current detection time indication associated with a time when the known mark was detected; and

computing the wedge frequency error based at least in part on the current detection time indication and a previous detection time indication.

19. A system as recited in claim 17 , wherein the lock criterion is met when, for each wedge-to-wedge time interval, the magnitude of the corresponding wedge frequency error is within a wedge frequency error limit for a predefined number of consecutive disk revolutions.

20. A system as recited in claim 17 , wherein after the lock criterion is met, computing a wedge frequency error is performed differently from before the lock criterion is met.

21. A system as recited in claim 17 , wherein the system is in a search state before the lock criterion is met and the system is in a lock state after the lock criterion is met.

22. A system for writing servo wedge code to a disk, comprising:

a processor configured to:

determine a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors; and

after the lock criterion is met, write servo wedge code to the disk, wherein after the lock criterion is met, the wedge frequency error is computed based at least in part on one or more of the following:

a target detection time indication defined as the value of the time stamp when changing to the lock state; or

a target detection time indication that stays the same during the lock state; and

a communication interface coupled to the processor.

23. A system for writing servo wedge code to a disk, comprising:

a processor configured to:

determine a wedge-to-wedge time interval;

at least until it is determined that a lock criterion is met:

for each wedge-to-wedge time interval, compute a wedge frequency error based on an adjustable clock to obtain a plurality of wedge frequency errors;

adjust the clock based on one or more of the plurality of wedge frequency errors; and

determine whether a lock criterion is met based on one or more of the plurality of wedge frequency errors; and

after the lock criterion is met, write servo wedge code to the disk, wherein:

the lock criterion is met if each of the wedge frequency errors is less than a wedge frequency error limit for a certain number of disk revolutions; and

the adjustable clock resets N wedge times per disk revolution, where N wedge is the number of wedges on the disk;

a communication interface coupled to the processor.