Read retry method in disk drive

Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction

Reexamination Certificate

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Details

C714S746000, C360S053000

Reexamination Certificate

active

06289483

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to disk drives such as CD-ROM (Compact Disk-Read Only Memory) drives, and more particularly, to a method for reducing read errors when reading data with a disk drive.
2. Description of the Related Art
Since a CD-ROM drive used in a contemporary personal computer or workstation accesses data at high speed such as 16× or 24× speed, read errors are likely to occur. Such a high-speed disk drive is designed to perform read retry processing that repeatedly attempts to read upon detecting a read error. Methods for the read retry processing are as follows: (1) a general method to retry reading for a prescribed number of times under the condition that the number of disk revolutions per unit time (i.e., disk revolution rate) is maintained at a given level; (2) a temporary decelerating method for reattempting to read by decreasing the disk revolution rate if an error is not corrected by the first general method, and for returning to the original disk revolution rate if the disk drive succeeds in reading; and (3) a decelerating method for reattempting to read by decreasing the disk revolution rate if an error is not corrected by the first general method, and for maintaining the revolution rate at the decreased level if the disk drive successfully reads.
The above methods for read retry processing have respective advantages and disadvantages. The first general method exhibits low error correcting capability because the disk revolution rate is always maintained at a given level. The second temporary decelerating method is superior in error correcting capability, but increases the load on the system. That is, the revolution of a spindle motor is frequently controlled, due to a frequent abrupt increase in the disk revolution rate to return to the original revolution rate after a corresponding abrupt decrease the revolution rate to overcome an error. Furthermore, the second temporary decelerating method may damage the disk because the disk returns to the original revolution rate after an error is corrected. Typically, the disk is damaged due to the abrupt changes in the revolution speed of the disk. The damaged part of the disk may generate a read error again and therefore it becomes difficult to decipher the data in the error-prone region. In the third decelerating method, the data transmission rate is lowered because the decreased disk revolution rate is maintained after an error occurs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a read retry method which has superior error correcting capability, and which can reduce read errors while maintaining a high data transmission rate.
According to an aspect of the present invention, there is provided a method for retrying a read operation upon detecting a read error of a disk drive, including the steps of decreasing the revolution rate of a disk until the read error is corrected; and if the read error is corrected, gradually increasing the revolution rate of the disk while a data read operation is performed.
The present invention improves error correcting capability by lowering the disk revolution rate when necessary. Once an error is corrected, the original disk revolution rate is not immediately returned to, in contrast to the conventional temporary decelerating method. Rather, the revolution rate is gradually increased in stages while a read operation is performed. Therefore, the next error can rapidly be detected before the revolution rate is significantly increased. As a result, unnecessary retrying time is diminished and the probability of generating an error reduced. Moreover, the spindle motor of the disk drive is prevented from revolving abruptly.
In an illustrative embodiment, if the disk drive succeeds in reading a prescribed number of data blocks after a read error is corrected, the disk revolution rate is gradually increased. The number of data blocks is set in accordance with the type of error detected, e.g., an ECC (Error Correction Code) error or a servo error. For the ECC error, the data blocks are set in consideration of a scratch or contamination of the disk. In the case of a servo error, the number of data blocks is set in consideration of the vibration of the disk.
The inventive read retry method can overcome an error at a maintainable maximum transmission rate because the number of revolutions of the disk is decreased in stages at the decreasing step. If a read error occurs again during the increasing step, the decreasing step is performed again. Therefore, an error can rapidly be sensed and an unnecessary retry operation omitted.


REFERENCES:
patent: 5432766 (1995-07-01), Ando et al.
patent: 5682272 (1997-10-01), Taroda et al.

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