Granted Patent B1

US 8,693,123 · App. 13/170,000 · Granted Apr 8, 2014

Abstract

Claims (42)

1. A disk drive comprising:

a disk comprising a plurality of tracks defined by a plurality of servo sectors;

a head actuated over the disk; and

control circuitry operable to:

generate an estimated track ID representing an estimated radial location of the head;

detect a high order Gray code in a first servo sector;

correct errors in the high order Gray code using the estimated track ID to generate a corrected Gray code;

decode the corrected Gray code into a first part of a detected track ID;

detect a low order track code in the first servo sector;

decode the low order track code into a second part of the detected track ID; and

combine the first part of the detected track ID with the second part of the detected track ID.

2. The disk drive as recited in claim 1 , wherein:

the high order Gray code comprises a plurality of bits recorded at a first linear density; and

the low order track code comprises a plurality of Gray coded bits recorded at a second linear density lower than the first linear density.

3. The disk drive as recited in claim 1 , wherein the low order track code comprises a plurality of redundancy bits such that at least one bit error is corrected when decoding the low order track code into the second part of the detected track ID.

4. The disk drive as recited in claim 1 , wherein the control circuitry is operable to correct errors in the high order Gray code by:

generating a plurality of proximate track IDs having values proximate the estimated track ID;

generating a set of Gray codes each corresponding to one of the proximate track IDs; and

correcting at least one bit in the high order Gray code in response to the set of Gray codes.

5. The disk drive as recited in claim 4 , wherein each Gray code in the set of Gray codes comprises N bits, and M bits out of the N bits comprise the same value, and the control circuitry is further operable to correct errors in the high order Gray code by inverting at least one bit in the high order Gray code comprising a value that is different from the value of the corresponding bit in the M bits.

6. A method of operating a disk drive, the disk drive comprising a head actuated over a disk comprising a plurality of tracks defined by a plurality of servo sectors, the method comprising:

generating an estimated track ID representing an estimated radial location of the head;

detecting a high order Gray code in a first servo sector;

correcting errors in the high order Gray code using the estimated track ID to generate a corrected Gray code;

decoding the corrected Gray code into a first part of a detected track ID;

detecting a low order track code in the first servo sector;

decoding the low order track code into a second part of the detected track ID; and

combining the first part of the detected track ID with the second part of the detected track ID.

7. The method as recited in claim 6 , wherein:

the high order Gray code comprises a plurality of bits recorded at a first linear density; and

the low order track code comprises a plurality of Gray coded bits recorded at a second linear density lower than the first linear density.

8. The method as recited in claim 6 , wherein the low order track code comprises a plurality of redundancy bits such that at least one bit error is corrected when decoding the low order track code into the second part of the detected track ID.

9. The method as recited in claim 6 , further comprising correcting errors in the high order Gray code by:

generating a plurality of proximate track IDs having values proximate the estimated track ID;

generating a set of Gray codes each corresponding to one of the proximate track IDs; and

correcting at least one bit in the high order Gray code in response to the set of Gray codes.

10. The method as recited in claim 9 , wherein each Gray code in the set of Gray codes comprises N bits, and M bits out of the N bits comprise the same value, and further comprising correcting errors in the high order Gray code by inverting at least one bit in the high order Gray code comprising a value that is different from the value of the corresponding bit in the M bits.

11. A method of writing a track ID in servo sectors of a disk drive to define a plurality of tracks on a disk, the method comprising:

encoding a plurality of most significant bits of the track ID into a first plurality of high order Gray code bits;

writing the high order Gray code bits to the disk at a first linear density;

encoding a plurality of least significant bits of the track ID into a second plurality of low order Gray code bits; and

writing the second plurality of low order Gray code bits to the disk at a second linear density lower than the first linear density.

Assignments (8)