Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data verification
Reexamination Certificate
2000-04-19
2003-08-12
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data verification
C360S031000
Reexamination Certificate
active
06606211
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a disc drive. More particularly, the present invention relates to a method and apparatus for detecting media defects in the disc drive.
BACKGROUND OF THE INVENTION
Before a disc drive leaves the factory it is scanned to determine the location of media defects that will give rise to problems in reading back data. Defect scanning is a time consuming process (upwards of 3 hours depending on the severity of the defects) which is exacerbated as the storage capacity of disc drives increases. Controllers associated with disc drives incorporate ECC (Error Correction Code) to reduce the incidence of errors when reading back data. A normal write, also known as sector write is commonly used to write data in a sector. Prior art defect scanning procedures assume a low level of error correction (say T
1
) to minimize risks of missing defects. This means that improved error correction (T
2
to T
5
) capabilities available in modern disc drives are not being fully utilized.
One prior art defect scan method involves writing a detect pattern. This is achieved by using a wedge write where writing is done from servo sector to servo sector. A wedge write normally contains three to four sectors depending on the way the media is zoned. A commonly used detect pattern is a 2T preamble synch pattern which follows from PRML (Partial Response Maximum Likelihood), a 5 level (+2, +1, 0, −1, −2) detect pattern. The synch pattern is read back whilst comparing it with a threshold value which should not be exceeded. Whenever the threshold value is exceeded a read error is flagged and the location which gives rise to the error is marked as a defect or a “bad” location. However, this process can give rise to an excessive number of defects, which reduces the capacity of the drive unnecessarily. To improve drive yield and speed up the defect scanning process it is desirable to avoid labelling as defects, locations which will give rise to errors that may be recovered by error correction.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for detecting media defects in a disc drive which addresses the above-mentioned problem.
The method of the present invention introduces a threshold on the number of location defects that may be tolerated before labelling the locations as bad. This may avoid labelling as bad, locations which will give rise to errors that may be recovered by error correction. It may also reduce substantially the time required for performing defect scanning. In one form the consecutive defects may be accumulated in a Consecutive Defect Counter (CDC). When the number of consecutive defects reaches a predetermined threshold value (say 5 bits long) the output of the CDC counter may flag a defect. The defect bit length may be controlled by an appropriate selection of the predetermined threshold value. In a typical implementation the CDC defect may be flagged as a set pattern (say FO Hex) on an NRZ (Non Return to Zero) 8 bit data output line associated with the CDC counter. The number of total defects may be accumulated in a Total Defect Counter (TDC). When the number of total defects reaches a predetermined threshold value (say 30 single bit defects, irrespective of the length of each bit), the output of the TDC counter may flag a defect. In a typical implementation the TDC defect may be flagged as a set pattern (say F1 Hex) on the NRZ 8 bit data output line associated with the TDC counter. One reason for having the CDC and TDC in this method is to enhance the limitations of the existing methods for detecting media defects. The manner of mapping the defect detected by the CDC and the TDC differ.
In prior art data is written either using sector write or wedge write. In the present invention, both sector and wedge write is used. If it is a CDC defect, that sector will be flagged as a defect. If it is a TDC defect, the entire wedge will be flagged as defective.
According to one aspect of the present invention there is provided a method for detecting defects in a recordable medium such as a disc drive. The method has a step for writing and reading test data on the medium. The method also has a step for comparing the read data to a first threshold. In another step of the method a first counter is incremented each time the first threshold is exceeded. The further step for providing a first defect signal when the counter reaches a predetecting count value is also part of this method.
The recordable medium may include a plurality of data domains for recording data. The method of the present invention may include the step of marking as bad, one or more of the data domains in response to the first defect signal.
The method of the present invention may include incrementing a second counter each time the first threshold is exceeded and producing a second defect signal when the second counter obtains a second count value. The data domains may be organized into data sectors. The method may include marking as bad, one or more of the data sectors in response to the second defect signal.
The method of the present invention may be implemented as a computer-readable program storage device which tangibly embodies a program of instructions executable by a computer system to perform the method.
According to another aspect of the present invention there is provided apparatus for detecting defects in a recordable medium such as a disc drive. The apparatus has a recording system for writing and reading test data on the medium. The apparatus also has a first comparator for comparing the read data to a first threshold. Another feature in the apparatus is a first counter operably connected to the first comparator, the first counter being incremented when the read data exceeds the first threshold. A single generator which produces a first defect signal when the first counter obtains a first count value also forms part of the apparatus.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.
REFERENCES:
patent: 4549295 (1985-10-01), Purvis
patent: 5031054 (1991-07-01), Lewis
patent: 5563746 (1996-10-01), Bliss
patent: 6151180 (2000-11-01), Bang
patent: 6175459 (2001-01-01), Tomita
Chong Fong Kheon
Lim Tuang Liang Bernard
Ngwe Myint
Teo Hwee Peng
Kapadia Varsha A.
McCarthy Mitchell K.
Seagate Technology LLC
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