Disk drive centering sync frames on sync marks of a spiral track

1. A disk drive comprising:

a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark;

a head actuated over the disk; and

control circuitry operable to:

use the head to read the spiral tracks to generate a read signal representing spiral track crossings;

first open a first sync frame in response to a first frame offset during a first revolution of the disk, wherein the first sync frame corresponds to the head approaching a first sync mark in a first spiral track crossing;

generate a first sync frame position error signal (PES) representing a difference between a target framing of the first sync frame around the first sync mark and a detected framing of the first sync frame around the first sync mark;

adjust the first frame offset in response to the first sync frame PES; and

second open the first sync frame in response to the adjusted first frame offset during a second revolution of the disk.

2. The disk drive as recited in claim 1 , wherein the target framing corresponds to the first sync mark occurring at a center of the first sync frame.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to synchronize a clock to a rotation of the disk in response to the sync frame PES.

4. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate the first sync frame by generating hardware control signals representing physical frame boundaries within the read signal.

5. The disk drive as recited in claim 4 , wherein the first frame offset is less than one-half the predetermined interval.

6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to generate the first sync frame by generating software control signals representing virtual boundaries within the read signal.

7. The disk drive as recited in claim 6 , wherein the first frame offset is greater than one-half the predetermined interval.

8. The disk drive as recited in claim 7 , wherein the first frame offset is greater than the predetermined interval.

9. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

position the head at an initial radial location over the disk; and

initialize the first frame offset.

10. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

first open a second sync frame in response a second frame offset during the first revolution of the disk, wherein the second sync frame corresponds to the head approaching a second sync mark in a second spiral track crossing;

generate a second sync frame position error signal (PES) representing a difference between a target framing of the second sync frame around the second sync mark and a detected framing of the second sync frame around the second sync mark;

adjust the second frame offset in response to the second sync frame PES; and

second open the second sync frame in response to the adjusted second frame offset during the second revolution of the disk.

11. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of spiral tracks, each spiral track comprising a high frequency signal interrupted at a predetermined interval by a sync mark, the method comprising:

using the head to read the spiral tracks to generate a read signal representing spiral track crossings;

first opening a first sync frame in response to a first frame offset during a first revolution of the disk, wherein the first sync frame corresponds to the head approaching a first sync mark in a first spiral track crossing;

generating a first sync frame position error signal (PES) representing a difference between a target framing of the first sync frame around the first sync mark and a detected framing of the first sync frame around the first sync mark;

adjusting the first frame offset in response to the first sync frame PES; and

second opening the first sync frame in response to the adjusted first frame offset during a second revolution of the disk.

12. The method as recited in claim 11 , wherein the target framing corresponds to the first sync mark occurring at a center of the first sync frame.

13. The method as recited in claim 11 , further comprising synchronizing a clock to a rotation of the disk in response to the sync frame PES.

14. The method as recited in claim 11 , further comprising generating the first sync frame by generating hardware control signals representing physical frame boundaries within the read signal.

15. The method as recited in claim 14 , wherein the first frame offset is less than one-half the predetermined interval.

16. The method as recited in claim 11 , further comprising generating the first sync frame by generating software control signals representing virtual boundaries within the read signal.

17. The method as recited in claim 16 , wherein the first frame offset is greater than one-half the predetermined interval.

18. The method as recited in claim 17 , wherein the first frame offset is greater than the predetermined interval.

19. The method as recited in claim 11 , further comprising:

positioning the head at an initial radial location over the disk; and

initializing the first frame offset.

20. The method as recited in claim 11 , further comprising:

first opening a second sync frame in response a second frame offset during the first revolution of the disk, wherein the second sync frame corresponds to the head approaching a second sync mark in a second spiral track crossing;

generating a second sync frame position error signal (PES) representing a difference between a target framing of the second sync frame around the second sync mark and a detected framing of the second sync frame around the second sync mark;

adjusting the second frame offset in response to the second sync frame PES; and

second opening the second sync frame in response to the adjusted second frame offset during the second revolution of the disk.