Patent ID: 6043946
Filing Date: 2000-03-28
Classification: G11B,H03M

Abstract:
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.