Disk drive employing a multiple-input sequence detector responsive to reliability metrics to improve a retry operation

• US 6,405,342 B1
• Filed: 09/10/1999
• Issued: 06/11/2002
• Est. Priority Date: 09/10/1999
• Status: Expired due to Term

• Current Assignee: Western Digital Corporation
• Original Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Inventors: Lee, Patrick J.
• Primary Examiner(s): Chung, Phung M.
• Application Number:
  US09/393,511
• Time in Patent Office: 1,005 Days
• Field of Search: 714/795, 714/792, 714/756, 714/755
• US Class Current: 714/792
• CPC Class Codes: G11B 20/1866 by interleaving G11B20/1809 takes precedence
• CPC Class Codes: G11B 2020/183 wherein at least one additional attempt is made to read or write the data when a first attempt is unsuccessful
• CPC Class Codes: H03M 13/2936 comprising an outer Reed-Solomon code and an inner convolutional code
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3723 using means or methods for the initialisation of the decoder
• CPC Class Codes: H03M 13/3769 using symbol combining, e.g. Chase combining of symbols received twice or more
• CPC Class Codes: H03M 13/41 using the Viterbi algorithm or Viterbi processors
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H03M 13/6343 Error control coding in combination with techniques for partial response channels, e.g. recording

Abstract

A disk storage system is disclosed employing an improved retry operation. The disk drive comprises a disk for storing a data block, and a head for reading the data block to generate an analog read signal during an initial read operation. A sampler samples the analog read signal to generate a sequence of read signal sample values, and a multiple-input sequence detector detects an initial estimated data sequence from the read signal sample values during the initial read operation. A reliability metrics generator generates reliability metrics representing an estimated reliability for data in the initial estimated data sequence, and the reliability metrics are stored in a local memory. During a retry operation, a memory controller transfers the reliability metrics generated during the initial read operation to the multiple-input sequence detector which generates a retry estimated data sequence using the reliability metrics, whereby the reliability metrics improves the probability of accurately detecting the retry estimated data sequence.

Claims

1. A disk drive (2) comprising:

(a) a disk (4) for storing a data block;

(b) a head (6) for reading the data block to generate an analog read signal (30) during an initial read operation;

(c) a sampler (46) for sampling the analog read signal (30) to generate a sequence of read signal sample values (52);

(d) a multiple-input sequence detector (58), responsive to the read signal sample values (52), for generating an initial estimated data sequence (60) during the initial read operation;

(e) a reliability metrics generator (62) for generating reliability metrics (64) representing an estimated reliability for data in the initial estimated data sequence (60);

(f) a local memory (66) for storing the reliability metrics (64); and

(g) a memory controller (68) for transferring the reliability metrics (64) stored in the local memory (66) to the multiple-input sequence detector (58);

wherein during a retry operation, the data block is reread from the disk (2), the memory controller (68) transfers the reliability metrics (64) generated during the initial read operation to the multiple-input sequence detector (58), and the multiple-input sequence detector (58) generates a retry estimated data sequence using the reliability metrics (64), whereby the reliability metrics improves the probability of accurately detecting the retry estimated data sequence.

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

(a) the multiple-input sequence detector comprises a metrics calculator for computing state metrics relative to the read signal sample values and expected sample values of valid output sequences; and

(b) during the retry operation, the computing of the state metrics is biased by the reliability metrics.

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

(a) the multiple-input sequence detector comprises a first iterative detector and a second iterative detector, and the metrics calculator for computing the state metrics comprises a first metrics calculator in the first iterative detector and a second metrics calculator in the second iterative detector;

(b) the first iterative detector generates first alternative reliability metrics for use by the second iterative detector, and the second iterative detector generates second alternative reliability metrics for use by the first iterative detector;

(c) the first iterative detector biases the computing of the state metrics using the second alternative reliability metrics;

(d) the second iterative detector biases the computing of the state metrics using the first alternative reliability metrics; and

(e) at least one of the iterative detectors biases the computing of the state metrics using the reliability metrics stored in the local memory.

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

(a) the initial estimated data sequence comprises at least two interleaved error correction code codewords comprising a plurality of bits;

(b) the reliability metrics generator comprises an error correction circuit which decodes at least one of the interleaved error correction code codewords into a decoded codeword; and

(c) the reliability metrics comprise bits of the decoded codeword.

5. The disk drive as recited in claim 4, wherein the initial estimated data sequence comprises a plurality of nibble interleaved error correction code codewords.

6. The disk drive as recited in claim 1, wherein the multiple-input sequence detector is a Viterbi sequence detector.

7. The disk drive as recited in claim 1, wherein the multiple-input sequence detector is an iterative detector.

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

(a) the reliability metrics generator is an iterative detector; and

(b) the local memory is integrated into the iterative detector.

9. The disk storage system as recited in claim 1, further comprising a samples buffer for storing the read signal samples during the initial read operation, wherein during the retry operation the multiple input sequence detector is responsive to the read signal samples stored in the samples buffer and the reliability metrics stored in the local memory for detecting the retry estimated data sequence while the disk storage medium is rotating to the beginning of the data block.

10. A method of improving a retry operation in a disk drive comprising the steps of:

(a) reading a data block stored on a disk to generate an analog read signal;

(b) sampling the analog read signal to generate a sequence of read signal sample values;

(c) detecting an estimated data sequence from the read signal sample values;

(d) computing reliability metrics representing an estimated reliability for data in the estimated data sequence;

(e) storing the reliability metrics in a local memory; and

(f) during a retry operation, repeating at least steps (a) through (c) wherein the step of detecting an estimated data sequence is responsive to the reliability metrics generated during a previous read operation which improves the probability of accurately detecting the estimated data sequence during the retry operation.

11. The method for detecting data recorded on a disk as recited in claim 10, wherein:

(a) the step of detecting the estimated data sequence from the read signal sample values comprises the step of computing state metrics relative to the read signal sample values and expected sample values of valid output sequences; and

(b) during the retry operation, the step of computing the state metrics is biased by the reliability metrics.

12. The method for detecting data recorded on a disk as recited in claim 10, wherein:

(a) the estimated data sequence comprises at least two interleaved error correction code codewords comprising a plurality of bits;

(b) the step of computing reliability metrics comprises the step of decoding at least one of the interleaved error correction code codewords into a decoded codeword; and

(c) the reliability metrics comprise bits of the decoded codeword.

13. The method for detecting data recorded on a disk as recited in claim 12, wherein the estimated data sequence comprises a plurality of nibble interleaved error correction code codewords.

14. The method for detecting data recorded on a disk as recited in claim 10, wherein the state metrics are associated with a trellis of a Viterbi sequence detector.

15. The method for detecting data recorded on a disk as recited in claim 10, wherein the state metrics are associated with a trellis of an iterative detector.

16. The method for detecting data recorded on a disk as recited in claim 10, wherein:

(a) the reliability metrics are generated by an iterative detector; and

(b) the local memory is integrated into the iterative detector.

17. The method for detecting data recorded on a disk as recited in claim 10, wherein the step of detecting the estimated data sequence further comprises the step of selectively biasing the computing of the state metrics using alternative reliability metrics generated by an iterative detector.

18. The method for detecting data recorded on a disk storage medium as recited in claim 10, further comprising the steps of;

storing the read signal samples in a samples buffer during the initial read operation; and

during the retry operation and while waiting for the disk storage medium to rotate to the beginning of the data block, detecting the retry estimated data sequence from the read signal samples stored in the samples buffer and the reliability metrics stored in the local memory.