Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-01-26
2002-08-27
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S794000, C369S047270
Reexamination Certificate
active
06442730
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a method and apparatus for analyzing a disk drive, and more particularly to a method and apparatus for determining the location and severity of errors on a disk drive or other appropriate recording medium.
Traditionally, in order to determine whether an error is present on a disk drive, it was necessary for an oscilloscope to be connected to the recording medium, and for a signal to be read from the recording medium. A technician manually scrolled through the signal depicted on the oscilloscope for the entire recording medium and visually reviewed the signal, looking for portions of the waveform that did not follow a regular, predictable pattern, to determine if there were any errors. Thus, by way of example, a technician might look at a signal output from a disk drive in order to insure that each of the waveforms has a similar amplitude within a certain tolerance. This method may be most easily used when recording media are encoded using a format known as “peak-detect” in which a technician must confirm that the peaks of all waveforms have consistent amplitude. As is evident, this analysis can be very time consuming since the technician must look at each waveform of the signals reproduced from the entire medium to detect an error. Also it is very difficult for a technician to detect all errors on the recording medium because of the volume of data and subtleness of the error detection.
Recently, drive-encoding format has changed from a peak-detect format to a PRML format. PRML format allows a signal to be checked at various points therealong, and not merely at the peak amplitude position, and thus allows more efficient encoding schemes. In accordance with various PRML formats, there may be anywhere from three to nine or more checkpoints or possible amplitude levels that indicate different data within a signal waveform. With the transition of drive technology from peak-detect to PRML format, interpretation of signal quality through visual analysis of the head signal (i.e., the signal reproduced from the recording medium) has become much more difficult. Whereas peak-detect signals could be analyzed by visual inspection of the location, quality and amplitude of peaks, analysis of PRML signals is much more difficult because of the complexity of PRML wave shapes and because the determination of whether a signal is “bad” or “good” is based on sophisticated processing of the head signal.
For this reason, it is very difficult to manually check a disk drive for errors. Therefore, it would be beneficial to provide an automated disk analysis apparatus and method that determine errors on a disk drive without the need for manual review of the reproduced signal from the entire medium.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the invention to provide an improved, automated disk drive failure analysis apparatus and method.
Another object of the invention is to provide an improved automated disk drive analysis apparatus and method which allows a user to automatically analyze a PRML signal received from a disk drive to determine the location of any errors contained therein.
A further object of the invention is to provide an improved automated disk drive analysis apparatus and method in which the PRML signal can be analyzed at any point in the disk drive from the pre-amp stage through output channel.
Yet another object of the invention is to provide an improved automated disk drive analysis apparatus and method which automatically and rapidly finds errors in the head recording signal by determining errors in the Non Return to Zero (NRZ) signal.
A still further object of the invention is to provide an improved automated disk drive analysis apparatus and method which allows a user to view the head signals determined to have errors along with ideal sample values.
Still another object of the invention is to provide an improved automated disk drive analysis apparatus and method which displays the byte offset indicative of the location of a particular error, or allows a user to view a portion of the output head signal at a particular desired byte offset.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification and drawings.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, an improved automated disk drive analysis apparatus and method are provided for automatically determining, finding and displaying errors present in the generated head signal of a disk drive. Thus, this improved apparatus and method of the invention improve the user's ability to:
Analyze PRML signals from the pre-amp through the output channel;
Rapidly find the location of errors on the head or NRZ signals;
View the head signal after equalization (Disk Drive Filter emulation);
Visually compare the equalized head signal to ideal samples values;
Determine the margin available to the Viterbi detector;
View the NRZ data, the corresponding sample values, Viterbi margin, equalized head signal and the direct head signal; and
Analyze the head signal directly.
For the remarkable gains in disk drive capacity to continue, media and head performance improvements are no longer enough. Faced with equally impressive advances in semiconductor technology, disk drive engineers have been working to create a new read-channel architecture that will allow capacity to grow unimpeded.
The answer lies in the construction of the disk itself. The disk's magnetic poles, with two orientations possible along the track, store the bits as “0” and “1”.
When the drive is used in a read operation, the head detects the transition from one pole to another—as bit “1” to bit “1”, for instance. If such transitions are far apart, or low-density, the drive will see isolated pulses. But for greater density, the pulses can either be made shorter, and therefore be placed closer together, or kept wide (longer) but allowed to overlap, and therefore need not return to zero between each pulse.
While the first of these alternatives, represented by Peak Detect systems, is believed to have reached its limits, the second-Partial-Response, Maximum Likelihood (PRML)—is currently seen as the best way to continue to boost capacity. However, additional channel types having superior characteristics, including a number of different algorithms and methods of analyzation, such as Decision Feedback Equalization (DFE), have been proposed, and are currently being developed. While the PRML channel is employed in a preferred embodiment of the invention, the invention is equally applicable to DFE, or any other channel types, which may be employed recording data on a recording medium.
The overlapping pulses of partial-response systems allow much greater density than the shorter isolated pulses of a peak detect system. PRML systems have more samples per “pw50”, which is defined as the width of an isolated pulse at 50% of its amplitude. The more complex, or higher-order, the PRML system, the greater the density that can be obtained. As is shown
FIG. 1
, comparing typical values achieved by available PRML systems with the values achieved by Peak Detect systems, it will be observed that the PRML values allow far denser, and therefore faster and more efficient, encoding schemes, such as E2PR4. PRML encoding schemes may have a density of 2.31 times that of a peak detect encoding scheme. However, the higher-order PRML schemes need very complex circuits and decoders. While the PR4 system works with three vertical levels of samples (encoding levels which must be differentiated), E2PR4 has seven vertical levels which must be differentiated and therefore requires not only a higher resolution of ADC, but a complicated timing and gain recovery circuit and sophisticated Maximum Likelihood detector as well.
Another disadvantage of the more complex PRML schemes is that they are more sensitive to noise.
The process of taking the more-or-less Lorentzian-shaped head response to a magnetic transition and turning it into a correctly
Bradick John
Lavanchy Didier Jean-Daniel
Max David P.
Salant Lawrence S.
Schachner Joseph M.
De'cady Albert
Frommer William S.
Frommer & Lawrence & Haug LLP
Kessler Gordon
Lamarre Guy
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