Read error recovery utilizing ECC and read channel quality indicators
First Claim
1. In a disc drive of the type having a rotatable disc which stores user data on tracks of the disc in the form of magnetic flux transitions generated by a read/write head adjacent the disc, the read/write head outputting a read signal during a disc drive read operation, the read signal indicative of the magnetic flux transitions from the disc, the disc drive further having a read channel for receiving the read signal and reconstructing the user data in the form of data symbols and corresponding code symbols from the read signal, the code symbols used to detect errors in the data symbols by error detection and correction circuitry of the read channel, the error detection and correction circuitry characterized as capable of correcting up to a selected number of detected errors in the data symbols and providing an indication when the number of detected errors exceeds the selected number of detected errors correctable by the error detection and correction circuitry, a method for performing a read operation comprising steps of:
- (a) determining a channel quality measurement indicative of error rate performance of the read channel, the channel quality measurement being determined from error values associated with the data symbols reconstructed by the read channel from the read signal;
(b) comparing the channel quality measurement to a predetermined measurement threshold, the predetermined measurement threshold selected to correspond to maximum acceptable probability of outputting at least one data symbol having an undetected error; and
(c) selectively using code symbols to correct data errors in the data symbols during the read operation based upon whether the channel quality measurement exceeds the predetermined measurement threshold.
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Accused Products
Abstract
An apparatus and method for recovering from read errors detected by a read channel (70) in a sequence of data read from a disc (18) of a disc drive (10) by using read channel quality indicators to determine the appropriateness of using error correction in combination with other corrective actions utilized in the recovery process. Upon the detection of an uncorrected error in the retrieved data, the disc drive (10) enters a read error recovery routine wherein one or more corrective actions (102, 122) are applied in an effort to resolve the error. One of the channel quality indicators comprises a channel quality measurement (108, 128) determined as the sum of the square of the sampled data bit error values recovered during the read operation. When the channel quality measurement is at or below a threshold value indicative that the probability of passing undetected erroneous data is at an acceptable level (110, 130), error correction is applied to the data (112, 138); otherwise, error correction is disallowed (118, 140). Additional channel quality indicators comprise erasure pointers (132) which identify a particular set of symbols that are suspected of containing a read error. In such a case, the disc drive determines that the total number of symbols identified by the erasure pointers is below a predetermined erasure threshold before applying error correction (134, 136, 138), the erasure threshold selected to be within the correction capability of error correction circuitry 90.
104 Citations
16 Claims
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1. In a disc drive of the type having a rotatable disc which stores user data on tracks of the disc in the form of magnetic flux transitions generated by a read/write head adjacent the disc, the read/write head outputting a read signal during a disc drive read operation, the read signal indicative of the magnetic flux transitions from the disc, the disc drive further having a read channel for receiving the read signal and reconstructing the user data in the form of data symbols and corresponding code symbols from the read signal, the code symbols used to detect errors in the data symbols by error detection and correction circuitry of the read channel, the error detection and correction circuitry characterized as capable of correcting up to a selected number of detected errors in the data symbols and providing an indication when the number of detected errors exceeds the selected number of detected errors correctable by the error detection and correction circuitry, a method for performing a read operation comprising steps of:
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(a) determining a channel quality measurement indicative of error rate performance of the read channel, the channel quality measurement being determined from error values associated with the data symbols reconstructed by the read channel from the read signal; (b) comparing the channel quality measurement to a predetermined measurement threshold, the predetermined measurement threshold selected to correspond to maximum acceptable probability of outputting at least one data symbol having an undetected error; and (c) selectively using code symbols to correct data errors in the data symbols during the read operation based upon whether the channel quality measurement exceeds the predetermined measurement threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A disc drive comprising:
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a disc having a plurality of tracks; an actuator adjacent the disc, the actuator comprising a read/write head capable of writing data to the tracks and reading data from the tracks in the form of a read signal; a read channel responsive to the read/write head, the read channel generating a sequence of data symbols and corresponding code symbols from the read signal, the read channel comprising; error detection and correction circuitry for detecting and correcting up to a selected number of data symbol errors in the sequence of data symbols, wherein the error detection and correction circuitry replaces the data symbol errors within the sequence of data symbols with correct data symbols, the correct data symbols based on the corresponding code symbols of the sequence of data symbols; and a quality monitor selectively generating a channel quality measurement indicative of performance quality of the read channel, the channel quality measurement generated from error values associated with the sequence of data symbols and corresponding code symbols; comparison means, responsive to the quality monitor, for comparing the channel quality measurement to a predetermined measurement threshold, the predetermined measurement threshold selected to correspond to a maximum acceptable probability of outputting at least one data symbol having an undetected error; and error correction control means, responsive to the comparison means, for controlling the correction of data symbol errors occurring within the sequence of data symbols, the correction based on the corresponding code symbols of the data symbols and in response to the comparison performed by the comparison means. - View Dependent Claims (13, 14, 15, 16)
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Specification