Error detection/correction and fault detection/recovery – Pulse or data error handling – Data formatting to improve error detection correction...
Reexamination Certificate
1999-12-06
2003-07-01
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Data formatting to improve error detection correction...
C714S769000, C341S059000
Reexamination Certificate
active
06587977
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for encoding data to be recorded in a data storage device (e.g. a disk drive) according to a run length limited (RLL) code. More particularly, the present invention relates to a method and apparatus for encoding data using a 0,k,m/m recording code. The present invention is particularly well suited for disk drives and other digital data storage devices, but is not necessarily limited to such devices (e.g. it might be used for digital data transmission).
BACKGROUND OF THE INVENTION
Background for the invention will be provided in connection with a disk drive system. It should be noted, however, that the present invention is not intended to be limited to such systems.
FIG. 1
illustrates a conventional disk drive system
100
. The disk drive system
100
is operative for performing data storage and retrieval functions for an external host computer
102
. The disk drive system
100
includes: a disk
104
, a transducer
106
, an actuator assembly
108
, a voice coil motor (VCM)
110
, a read/write channel
112
, an encoder/decoder (ENDEC)
114
, an error correction coding (ECC) unit
116
, a data buffer memory
118
, an interface unit
120
, a servo unit
122
, and a disk controller/microprocessor
124
.
In general, disk
104
includes a pair of disk surfaces (not shown) which are coated with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field. Data is stored digitally in the form of magnetic polarity transitions (frequently referred to as pulses) within concentric tracks on one or more of the disk surfaces. The disk
104
is rotated at a substantially constant spin rate by a spin motor (not shown) that is speed-controlled by a closed loop feedback system. Instead of the single disk
104
shown in
FIG. 1
, the system
100
can include a plurality of disks all mounted on a single spindle and each serviced by one or more separate transducers.
The transducer
106
is a device that transfers information from/to the disk
104
during read and write operations. The transducer
106
is positioned over the disk
104
, typically, by a rotary actuator assembly
108
that pivots about an axis under the power of the VCM
110
. During a write operation, a polarity-switchable write current is delivered to the transducer
106
from the read/write channel
112
to induce magnetic polarity transitions onto a desired track of the disk
104
. During a read operation, the transducer
106
senses magnetic polarity transitions on a desired track of the disk
104
to create an analog read signal that is indicative of the data stored thereon. Commonly, the transducer
106
is a dual element head having a magnetoresistive read element and an inductive write element.
The VCM
110
receives movement commands from the servo unit
122
for properly positioning the transducer
106
above a desired track of the disk
104
during read and write operations. The servo unit
122
is part of a feedback loop that uses servo information from the surface of the disk
104
to control the movement of the transducer
106
and the actuator assembly
108
in response to commands from the controller/microprocessor
124
.
During a read operation, the channel
112
receives the analog read signal from the transducer
106
and processes the signal to create a digital read signal representative of the data stored on the disk
104
. Typically, detection circuitry is included in the channel
112
. The channel
112
may also include means for deriving timing information, such as a read clock, from the analog signal.
The ENDEC
114
is operative for: (1) encoding data being transferred from the host
102
to the disk
104
, and (2) decoding data being transferred from the disk
104
to the host
102
. Data being written to the disk
104
is encoded for a number of reasons, including those relating to timing and detection concerns. The ENDEC generally imparts a run length limited (RLL) code on the data being written to the disk
104
to ensure that the frequency of transitions in the bit stream does not exceed or fall below predetermined limits. Such coding ensures that, among other things, enough transitions exist in the read data to maintain an accurate read clock. Other coding schemes may also be employed in the ENDEC
114
.
The ECC unit
116
is operative for adding redundant information to the data from the host
102
before that data is encoded in the ENDEC
114
and written to the disk
104
. This redundant information is used during subsequent read operations to permit discovery of error locations and values within the decoded read data. Errors in the read data detected by the ECC unit
116
can result from any number of mechanisms, such as: (1) media noise due to media anomalies, (2) random noise from the transducer, cabling and electronics, (3) poor transducer placement reducing signal amplitude and/or increasing adjacent track noise during the read operation, (4) poorly written data due to media defects or poor transducer placement, and/or (5) foreign matter on the media or media damage. ECC units are generally capable of correcting up to a predetermined number of errors in a data block. If more that the predetermined number of errors exist, then the code will not be able to correct the errors but may still be able to identify that errors exist within the block. ECC functionality is generally implemented in a combination of hardware and software.
The data buffer memory
118
is used to temporarily store data for several purposes:
(1) to permit data rates that are different between the disk drive and the host interface bus,
(2) to allow time for the ECC system to correct data errors before data is sent to the host
102
,
(3) temporary parameter storage for the controller/microprocessor
124
, and (4) for data caching.
The interface
120
is used to establish and maintain communication between the host
102
and the disk drive system
100
. In this regard, all transfer of information into and out of the disk drive
100
takes place through the interface
120
.
The disk controller/microprocessor
124
is operative for controlling the operation and timing of the other elements of the system
100
. In addition, the controller/microprocessor
124
may perform the functions of some of the elements of the system. For example, the controller/microprocessor
124
may perform the correction computation function of the ECC unit
116
if errors exceed the capability of the hardware based unit.
With this background, certain drawbacks associated with conventional disk drive encoding and decoding schemes may now be considered.
As alluded to above, clock information is typically embedded into data stored onto the disk
104
. In order to ensure that an adequate and timely supply of clock information is provided for the clock extraction process (which is performed by the channel
112
), and perhaps for other reasons, run length limited (RLL) codes are employed. As is understood by those skilled in the art (and therefore will not be described herein), detected data includes clock phase error information that is used in the clock extraction process.
RLL codes are traditionally described as d,k codes, where d is the minimum run length and k is the maximum run length between magnetic transitions. Note that two data representation conventions are frequently used, NRZ (non-return to zero) and NRZI (non-return to zero, change on ones). If NRZ, a magnetic polarity transition occurs when a sequence (one or more) of 0's changes to a sequence of 1's, or vice versa. If NRZI, a magnetic polarity transition occurs each time a 1 appears and 0's appear otherwise. While either convention is acceptable and supportable by this invention, NRZ will be used herein to describe the encode and decode processes. Using either convention, d represents the minimum number of bits that must exist between magnetic polarity transitions, while k represents the maximum number bits that may exist between magnetic polarity
Riggle C. M. (Mike)
VanLaanen John W.
De'cady Albert
Dooley Matthew C.
Hansra Tejpal S.
Maxtor Corporation
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