Error checking in a disk drive system using a modulo code

Details Error checking in a disk drive system using a modulo code Error checking in a disk drive system using a modulo code

2000-03-03

2004-03-16

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data verification

C360S039000

Reexamination Certificate

active

06707627

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to the field of disk drive systems, and in particular to disk drive systems and circuitry that encode and decode data using a modulo code for error checking.
2. Statement of the Problem
FIG. 1
shows a conventional disk drive system
100
. The disk drive system
100
includes a disk device
102
connected to control circuitry
106
. The disk device
102
includes storage media
104
that stores data. Some examples of the storage media
104
are magnetic and optical disks. The control circuitry
106
includes a read channel circuit
120
and a write channel circuit
140
. The write channel circuit
140
transfers signals to the disk device
102
to store data. The read channel circuit
120
processes signals from the disk device
102
to reproduce the stored data. The write channel circuit
140
includes an encoder
142
, a write compensation circuit
144
, and an interface
146
all connected in series. The read channel circuit
120
includes a sampling circuit
122
, an adaptive filter
124
, an interpolated timing recovery (I.T.R.) circuit
126
, a detector
128
, and a decoder
130
all connected in series.
If the storage media
104
is a magnetic disk, then the data is exchanged with the magnetic disk as follows. The write channel circuit
140
generates a write signal
111
representing user data
141
. The write signal
111
drives a magnetic head in the disk device
102
. The magnetic head alters a magnetic field to create magnetic transitions on the magnetic disk. These magnetic transitions represent the data. The head subsequently detects the magnetic transitions to generate a read signal
110
that represents the magnetic transitions. The read channel circuit
120
processes the read signal
110
to produce a data signal
131
that represents the data.
If the storage media
104
is an optical disk, then the data is exchanged with the optical disk as follows. The write channel circuit
140
generates a write signal
111
representing the user data
141
. The write signal
111
drives a device that creates pits in the surface of the optical disk. The pits create physical transitions that represent the data. An optical pick-up projects a laser onto the surface of the disk and detects the reflection to generate the read signal
110
that represents the physical transitions. The read channel circuit
120
processes the read signal
110
to produce the data signal
131
that represents the data.
To read or write the data, the magnetic head or optical pick-up must first be positioned over a certain track. To facilitate this positioning, servo information that identifies various locations on the disk is stored on the disk at the corresponding locations. The read signal
110
includes this servo information. The control circuitry
106
processes the servo information to control the positioning of the disk device
102
.
The write channel circuit
140
operates as follows to store data on the disk device
102
. The encoder
142
receives the user data
141
. The encoder
142
encodes the user data
141
so that error-checking functions can be performed on the user data
141
when it is subsequently decoded. The encoder
142
transfers a digital signal
143
representing the encoded user data
141
to the write compensation circuit
144
. The write compensation circuit
144
receives the digital signal
143
and adjusts the timing of the transitions in the digital signal
143
. The write compensation circuit
144
transfers the digital signal
143
to the interface
146
. The interface
146
receives the digital signal
143
and converts from digital to analog to form the write signal
111
. The interface
146
transfers the write signal
111
to the disk device
102
.
The read channel circuit
120
operates as follows to convert the read signal
110
into the data signal
131
. The sampling circuit
122
converts the read signal
110
from analog to digital by sampling the read signal
110
to generate read samples
123
for the adaptive filter
124
. The adaptive filter
124
removes distortion by shaping the read samples
123
to generate equalized samples
125
for the I.T.R. circuit
126
. The J.T.R. circuit
126
synchronizes the equalized samples
125
with the detector
128
clock by interpolating the equalized samples
125
at the detector
128
clock pulses to generate interpolated samples
127
. The detector
128
converts the interpolated samples
127
into an encoded bit stream
129
by processing the interpolated samples
127
with a detection algorithm, such as a Viterbi state machine. The decoder
130
decodes the encoded bit stream
129
into the data signal
131
by applying a decoding technique, such as PR4 with D=1 constraints. The decoder
130
also performs error-checking functions on the data signal
131
.
FIG. 2
illustrates how the encoder
142
encodes the user data
141
. The encoder
142
separates the user data
141
into blocks, including a first data block
210
, and a second data block
220
. The encoder
142
inserts first stuff bits
231
-
232
between the first data block
210
and the second data block
220
. The first stuff bits
231
-
232
are stripped out when the user data
141
is later decoded.
FIG. 3
shows a logical table that illustrates how the encoder
142
determines the values to insert into the first stuff bits
231
-
232
. The encoder
142
utilizes non-return to zero invertive (NRZI) transition encoding, meaning that the presence or absence of a transition in the data signifies a bit. The encoder
142
maintains a D=1 constraint when encoding, meaning that at least one zero is required between consecutive ones. The encoder
142
looks at the last bit
211
of the first data block
210
and the first bit
221
of the second data block
220
when determining the values to insert into the first stuff bits
231
-
232
. When the last bit
211
is a “0” and the first bit
221
is a “0”, the encoder
142
inserts a “0” or “1” for the first stuff bits
231
-
232
so as to maintain the D=1 constraint. When the last bit
211
is a “1” and the first bit
221
is a “0”, the encoder
142
inserts a “0” for stuff bit
231
. The encoder
142
inserts a parity value for stuff bit
232
. The parity value is commonly the parity of either the even or odd NRZI bits of the first data block
210
. Parity checking such as this is well known in the art. When the last bit
211
is a “0” and the first bit
221
is a “1”, the encoder
142
inserts a parity value for stuff bit
231
. The parity value is commonly the parity of either the even or odd NRZI bits of the first data block
210
. The encoder
142
inserts a “0” for stuff bit
232
.
The decoder
130
checks for errors in the encoded bit stream
129
by using a parity check. The encoded bit stream
129
represents a third data block and second stuff bits. The decoder
130
starts by checking the parity of the third data block. The parity check commonly takes place over the even or odd NRZI bits of the third data block. The decoder
130
detects errors by comparing the parity of the third data block with the parity value inserted in the second stuff bits. If the parity values are the same, then no error is detected. If the parity values are different, then an error is detected. The same parity check takes place over all data blocks.
The problem with the current disk drive system
100
is that it provides insufficient error detection. The current detector
128
commonly produces bit shift errors in the process of converting the read signal
110
into the data signal
131
. The error-checking method in the prior art often does not detect the bit-shift errors and fails to detect other types of errors. Reliability of the disk drive system
100
needs to be improved.
SUMMARY OF THE SOLUTION
The invention solves the above problem by providing error detection using a modulo code. The modulo code allows the disk drive system to detect bit shifts and other errors that may not be detected by the prior systems.

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