Title: Servo synchronization based on a servo synch mark that conflicts with self-clocking encoding algorithms
Abstract: Disclosed is a rotatable media storage device (RMSD) that performs servo synchronization based on a servo synch mark (SSM) that conflicts with self-clocking encoding algorithms. The RMSD includes a disk having a plurality of tracks wherein each track comprises a plurality of data regions interspersed between servo wedges. The servo wedges comprise a servo synch mark field including a servo synch mark (SSM) and a track identification field including a track identifier (TKID). The TKID is encoded in accordance with a self-clocking encoding algorithm whereas the SSM is encoded in accordance with a second algorithm that conflicts with the self-clocking encoding algorithm of the TKID. Thus, the SSM is prevented from being decoded as a portion of the TKID.
Patent Number: 6,934,104 Issued on 08/23/2005 to Kupferman
| Inventors:
|
Kupferman; Hanan (Diamond Bar, CA)
|
| Assignee:
|
Western Digital Technologies, Inc. (Lake Forest, CA)
|
| Appl. No.:
|
857553 |
| Filed:
|
May 28, 2004 |
| Current U.S. Class: |
360/51; 360/48 |
| Intern'l Class: |
G11B 005/09 |
| Field of Search: |
360/48,51
|
References Cited [Referenced By]
U.S. Patent Documents
| 5162791 | Nov., 1992 | Heegard.
| |
| 6178056 | Jan., 2001 | Cloke et al.
| |
| 6671115 | Dec., 2003 | Haraguchi et al.
| |
| Foreign Patent Documents |
| 0 553 409 | Aug., 1993 | EP.
| |
| 553409 | Aug., 1993 | EP.
| |
Primary Examiner: Hudspeth; David
Assistant Examiner: Mercedes; Dismery
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman
Claims
1. A rotating media storage device (RMSD) including a disk, the disk comprising:
a plurality of tracks, each track comprising a plurality of data regions interspersed
between servo wedges, the servo wedges comprising:
a servo synch mark field including a servo synch mark (SSM);
a track identification field including a track identifier (TKID);
wherein the TKID is encoded in accordance with a self-clocking encoding algorithm
and the SSM is encoded in accordance with a second algorithm that conflicts with
the self-clocking encoding algorithm; and
wherein the SSM is prevented from being decoded as a portion of the TKID.
2. The RMSD of claim 1, further comprising a head and a synch mark detection
circuit having a synch mark detection mode, wherein, in the synch mark detection
mode, the synch mark detection circuit validates a servo synchronization signal
based on the head detecting an encoded pattern of the SSM that conflicts with the
self-clocking encoding algorithm of the TKID.
3. The RMSD of claim 2, wherein the synch mark detection circuit further,
reads an encoded pattern of the SSM; and
decodes the encoded pattern of the SSM.
4. The RMSD of claim 3, wherein the synch mark detection circuit further comprises
a matched filter to match the encoded pattern of the SSM with a SSM validation
pattern in order to validate the servo synchronization signal.
5. The RMSD of claim 3, further comprising a read/write channel, wherein the
read/write channel decodes an encoded pattern of the TKID.
6. The RMSD of claim 1, wherein at least some of the servo wedges further include
a wedge identifier (ID) having an encoded pattern that is in accordance with the
self-clocking encoding algorithm of the TKID.
7. The RMSD of claim 1, wherein the SSM is located adjacent to the TKID.
8. The RMSD of claim 1, wherein the SSM is not located adjacent to the TKID.
9. The RMSD of claim 1, wherein the self-clocking encoding algorithm of the TKID
is compatible with a Manchester encoding scheme.
10. The RMSD of claim 1, wherein the encoding algorithm of the SSM conflicts
with a Manchester encoding scheme.
11. A method for performing servo synchronization in a rotating media storage
device (RMSD) including a disk having a plurality of tracks, each track comprising
a plurality of data regions interspersed between servo wedges, the servo wedges
including a servo synch mark field including a servo synch mark (SSM) and a track
identification field including a track identifier (TKID), wherein the TKID is encoded
in accordance with a self-clocking encoding algorithm and the SSM is encoded in
accordance with a second algorithm that conflicts with the self-clocking encoding
algorithm, the method comprising:
monitoring for an SSM; and
detecting a pattern of an SSM that conflicts with the self-clocking encoding
algorithm of the TKID.
12. The method of claim 11, wherein detecting a pattern of an SSM that conflicts
with the self-clocking encoding algorithm of the TKID further comprises:
reading an encoded pattern of the SSM; and
decoding the encoded pattern of the SSM.
13. The method of claim 12, wherein detecting a pattern of an SSM that conflicts
with the self-clocking encoding algorithm of the TKID further comprises matching
the encoded pattern of the SSM with a SSM validation pattern.
14. The method of claim 11, wherein at least some of the servo wedges further
include a wedge identifier (ID) having an encoded pattern that is in accordance
with the self-clocking encoding algorithm of the TKID.
15. The method of claim 11, wherein the SSM is located adjacent to the TKID.
16. The method of claim 11, wherein the SSM is not located adjacent to the TKID.
17. The method of claim 11, wherein the self-clocking encoding algorithm of the
TKID is compatible with a Manchester encoding scheme.
18. The method of claim 11, wherein the encoding algorithm of the SSM conflicts
with a Manchester encoding scheme.
19. A computer system comprising a host computer and a rotating media storage
device (RMSD) connected to the host computer, the RMSD comprising:
a disk having a plurality of tracks, each track comprising a plurality of data
regions interspersed between servo wedges, the servo wedges comprising:
a servo synch mark field including a servo synch mark (SSM);
a track identification field including a track identifier (TKID);
wherein the TKID is encoded in accordance with a self-clocking encoding algorithm
and the SSM is encoded in accordance with a second algorithm that conflicts with
the self-clocking encoding algorithm; and
wherein the SSM is prevented from being decoded as a portion of the TKID.
20. The computer system of claim 19, further comprising a head and a synch mark
detection circuit having a synch mark detection mode, wherein, in the synch mark
detection mode, the synch mark detection circuit validates a servo synchronization
signal based on the head detecting an encoded pattern of the SSM that conflicts
with the self-clocking encoding algorithm of the TKID.
21. The computer system of claim 20, wherein the synch mark detection circuit
further, reads an encoded pattern of the SSM; and
decodes the encoded pattern of the SSM.
22. The computer system of claim 21, wherein the synch mark detection circuit
further comprises a matched filter to match the encoded pattern of the SSM with
a SSM validation pattern in order to validate the servo synchronization signal.
23. The computer system of claim 21, further comprising a read/write channel,
wherein the read/write channel decodes an encoded pattern of the TKID.
24. The computer system of claim 19, wherein at least some of the servo wedges
further include a wedge identifier (ID) having an encoded pattern that is in accordance
with the self-clocking encoding algorithm of the TKID.
25. The computer system of claim 19, wherein the SSM is located adjacent to the TKID.
26. The computer system of claim 19, wherein the SSM is not located adjacent
to the TKID.
27. The computer system of claim 19, wherein the self-clocking encoding algorithm
of the TKID is compatible with a Manchester encoding scheme.
28. The computer system of claim 20, wherein the encoding algorithm of the SSM
conflicts with a Manchester encoding scheme.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to rotating media storage devices (RMSDs). More
particularly, the present invention relates to an RMSD that performs servo synchronization
based on a servo synch mark (SSM) that conflicts with self-clocking encoding algorithms.
2. Description of the Prior Art and Related Information
Computer systems rely on rotating media storage devices (RMSDs), which often
employ a moveable head actuator to frequently access large amounts of data stored
on the media. One example of an RMSD is a hard disk drive. A conventional hard
disk drive has a head disk assembly ("HDA") including at least one magnetic disk
("disk"), a spindle motor for rapidly rotating the disk, and a head stack assembly
("HSA") that includes a head gimbal assembly (HGA) with a moveable transducer head
for reading and writing data. The HSA forms part of a servo control system that
positions the transducer head over a particular track on the disk to read or write
information from and to that track, respectively.
With reference to FIG. 1, FIG. 1 shows an example of a prior art disk
10
having a plurality of concentric tracks
12. Each surface of each disk
10
conventionally contains a plurality of concentric data tracks
12 angularly
divided into a plurality of data sectors
15. In addition, special servo
information is provided on each disk to determine the position of the moveable
transducer head.
The most popular form of servo is called "embedded servo" wherein the servo information
is written in a plurality of servo wedges
14a,
14b,
etc. that are angularly spaced from one another and are interspersed between data
sectors
15 around each track of each disk.
Each servo wedge
14 typically includes a phase lock loop (PLL) field
20, a servo synch mark (SSM) field
22, a track identification (TKID)
field
24, a wedge ID field
26 having a binary encoded wedge ID number
to identify the wedge, and a group of servo bursts (e.g. ABCD)
26 (e.g.
an alternating pattern of magnetic transitions) which the servo control system
samples to align the moveable transducer head with or relative to a particular track.
Typically, the servo control system moves the transducer head toward a
desired track during a coarse "seek" mode using the TKID field as a control input.
However, in processing information, it is necessary to ensure consistency in the
detection of bits composing a block of bits. One common approach directed to ensuring
such consistency employs multiple stored fields including a phase lock loop (PLL)
field
20 to facilitate bit synchronization and a synch field to facilitate
block synchronization. The synch mark field facilitates block synchronization by
holding a special marker that is detected to "frame" data, i.e., to identify a
boundary of a block. In contemporary hard disk drives employing embedded servos,
it is well known to provide framing of servo data via a servo synch mark (SSM)
field
22.
Generally, in hard disk drives, a servo synchronization signal based on
the head reading a servo synchronization mark (SSM) results in a read/write channel
of the disk drive establishing a precise timing reference point for read/write operations.
Once the transducer head is generally over the desired track, the servo control
system uses the servo bursts (e.g. ABCD)
28 to keep the transducer head
over that track in a fine "track follow" mode. During track following mode, the
moveable transducer head repeatedly reads the wedge ID field
26 of each
successive servo wedge
14 to obtain the binary encoded wedge ID number that
identifies each wedge of the track. In this way, the servo control system continuously
knows where the moveable head is relative to the disk.
As previously discussed, a servo synchronization signal based on the head reading
a servo synchronization mark (SSM)
22 typically causes a read/write channel
of a disk drive to establish a precise timing reference point for any read/write
operations. Thus, it is important that the servo synchronization signal be robust
and timely. To that end, the SSM pattern should be unique such that it will not
be identified in other areas of the servo wedge. Particularly, it is important
that the SSM pattern not be mistakenly identified as the TKID field
24,
the wedge ID field
26, the servo bursts (e.g. ABCD)
28, etc.
Typically in most disk drives, the SSM
22, the TKID
24, and
the wedge ID
26 are all recorded and encoded in accordance with a self-clocking
encoding algorithm on the disk. Self-clocking encoding algorithms provide an encoding
method in which data as well as clocking is integrated into one encoded pattern.
One of the most commonly used types of self-clocking encoding algorithms is Manchester encoding.
Turning now to FIG. 2, FIG. 2 illustrates an example 2 of Manchester encoding.
As can be seen in FIG. 2, Manchester encoding defines the time required to define
a bit into two cycles. In one example 3, an up-going pulse, defines a data value
of "1" by having a first cycle of positive bits (1, 1) followed by a down-cycle
of zero bits (0,0). A series of all data "1's" in accordance with Manchester encoding
can be seen in pattern
5. The dashed lines represent the read-back signal
generated by the head of the disk drive as it reads the encoded pattern. Conversely,
as shown in example 4, a data value of "0" in Manchester encoding can be defined
as a down-going pulse having a first cycle of two zero bits (0,0) followed by an
up-cycle of positive bits (1, 1). A series of all data "0's" in accordance with
Manchester encoding can be seen in pattern
6. The dashed lines represent
the read-back signal generated by the head of the disk drive as it reads the encoded
pattern. Further, an example pattern of data bits, e.g. 1, 0, 1, 1, 1 in accordance
with Manchester encoding, as recorded on the disk, can be seen as example pattern
7. Again, the dashed lines represent the read-back signal generated by the
head of the disk drive as it reads the encoded pattern. It should be appreciated
that this is one example of Manchester encoding and other variations are possible.
In current disk drives, this type of self-clocking Manchester encoding is typically
used in encoding the SSM
22, the TKID
24, and the wedge ID
26.
Because the SSM, the TKID, and the wedge ID all utilize the same self-clocking
Manchester encoding algorithm, they are more likely to be misrecognized as one another.
However, if the SSM pattern is mistakenly identified in one of the other
areas of the servo wedge, read/write operations may be compromised resulting in
the wrong data being read, or, data being written to areas of the disk that is
not supposed to be. Unfortunately, due to the fact that all of these various servo
wedge components utilize the same self-clocking Manchester encoding algorithm,
there is a greater likelihood that the SSM pattern will be misrecognized in other
areas of the servo wedge.
SUMMARY OF THE INVENTION
The present invention relates to servo synchronization based on a servo synch
mark (SSM) that conflicts with self-clocking encoding algorithms in a rotating
media storage device (RMSD).
In one aspect, the invention may be regarded as an RMSD including a disk. The
disk includes a plurality of tracks wherein each track comprises a plurality of
data regions interspersed between servo wedges. The servo wedges comprise a servo
synch mark field including a servo synch mark (SSM) and a track identification
field including a track identifier (TKID). The TKID is encoded in accordance with
a self-clocking encoding algorithm whereas the SSM is encoded in accordance with
a second algorithm that conflicts with the self-clocking encoding algorithm of
the TKID. Thus, the SSM is prevented from being decoded as a portion of the TKID.
In one embodiment, the RMSD may further include a head and a synch mark detection
circuit. The synch mark detection circuit includes a synch mark detection mode
in which the synch mark detection circuit validates a servo synchronization signal
based on the head detecting an encoded pattern of the SSM that conflicts with the
self-clocking encoding algorithm of the TKID. The synch mark detection circuit
typically reads an encoded pattern of the SSM and decodes the encoded pattern of
the SSM. In one embodiment, the synch mark detection circuit further comprises
a matched filter to match the encoded pattern of the SSM with a SSM validation
pattern in order to validate the servo synchronization signal. Further, a read/write
channel may decode an encoded pattern of the TKID.
In one embodiment, at least some of the servo wedges may include a wedge identifier
(ID) having an encoded pattern that is in accordance with the self-clocking encoding
algorithm of the TKID. The SSM may or may not be located adjacent to the TKID.
In one embodiment, the self-clocking encoding algorithm of the TKID is compatible
with a Manchester encoding scheme. Further, in one embodiment, the encoding algorithm
of the SSM conflicts with the Manchester encoding scheme.
In a further aspect, the invention may be regarded as a method for performing
servo synchronization in a RMSD including a disk having a plurality of tracks wherein
each track comprises a plurality of data regions interspersed between servo wedges.
The servo wedges may include a servo synch mark field including a servo synch mark
(SSM) and a track identification field including a track identifier (TKID). The
TKID is encoded in accordance with a self-clocking encoding algorithm and the SSM
is encoded in accordance with a second algorithm that conflicts with the self-clocking
encoding algorithm. The method includes monitoring for the SSM. The method further
includes detecting a pattern of an SSM that conflicts with the self-clocking encoding
algorithm of the TKID.
In yet another aspect, the invention may be regarded as a computer system including
a host computer and an RMSD, in which the RMSD includes a disk having a plurality
of tracks, wherein each track includes a plurality of data regions interspersed
between servo wedges. The servo wedges include a servo synch mark field including
a servo synch mark (SSM) and a track identification field including a track identifier
(TKID). The TKID is encoded in accordance with a self-clocking encoding algorithm
whereas the SSM is encoded in accordance with a second algorithm that conflicts
with the self-clocking encoding algorithm of the TKID. Thus, the SSM is prevented
from being decoded as a portion of the TKID.
The foregoing and other features of the invention are described in detail in
the Detailed Description and are set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an example of a prior art disk having a plurality of concentric tracks.
FIG. 2 illustrates an example of Manchester encoding.
FIG. 3 shows a block diagram of a rotating media storage device (RMSD), such
as a disk drive 30, in which embodiments of the invention may be practiced.
FIG. 4 shows a disk of a disk drive having a plurality of concentric tracks,
and more particularly, illustrates a servo synch mark (SSM) that conflicts with
the self-clocking encoding algorithm of the other components of the servo wedge,
according to one embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of an SSM pattern that conflicts
with self-clocking encoding algorithms.
FIG. 6 is a flow chart of a method, according to one embodiment of the invention,
for implementing servo synchronization techniques based on a servo synch mark (SSM)
that conflicts with self-clocking encoding algorithms.
FIG. 7 is a block diagram of an example of a circuit that may be used in the
synch mark detection circuit to validate a SSM, according to one embodiment of
the present invention.
DETAILED DESCRIPTION
In the following description, the various embodiments of the invention will be
described in detail. However, such details are included to facilitate understanding
of the invention and to describe exemplary embodiments for employing the invention.
Such details should not be used to limit the invention to the particular embodiments
described because other variations and embodiments are possible while staying within
the scope of the invention. Furthermore, although numerous details are set forth
in order to provide a thorough understanding of the embodiments of the invention,
it will be apparent to one skilled in the art that these specific details are not
required in order to practice the embodiments of the invention. In other instances
details such as, well-known methods, types of data, protocols, procedures, components,
electrical structures and circuits, are not described in detail, or are shown in
block diagram form, in order not to obscure the invention. Moreover, embodiments
of the invention will be described in particular embodiments but may be implemented
in hardware, software, firmware, middleware, or a combination thereof.
FIG. 3 shows a block diagram of a rotating media storage device (RMSD), such
as a disk drive
30, in which embodiments of the invention may be practiced.
One suitable standard for such connection is the Advance Technology Attachment
(ATA) standard presently favored for desktop personal computers. Disk drive
30
comprises a Head/Disk Assembly, HDA
34, and a controller printed circuit
board assembly, PCBA
32.
The HDA
34 comprises: one or more disks
46 for data storage; a
spindle motor
50 for rapidly spinning each disk
46 (four shown) on
a spindle
48; and an actuator assembly
40 for moving a plurality
of heads
64 in unison over each disk
46. The heads
64 are
connected to a preamplifier
42 via a cable assembly
65 for reading
and writing data on disks
46. Preamplifier
42 is connected to channel
circuitry in controller PCBA
32 via read data line
92 and write data
line
90.
Controller PCBA
32 comprises a read/write channel
68, servo
controller
98, host interface and disk controller HIDC
74, voice
coil motor driver VCM
102, spindle motor driver SMD
103, microprocessor
84, and several memory arrays-buffer or cache memory
82, RAM
108,
and non-volatile memory
106.
Read/write channel
68 may include a servo synch mark detection
circuit
69, which under the control of a program or routine, may execute
methods or processes in accordance with embodiments of the invention to perform
servo synchronization based on a servo synch mark that conflicts with self-clocking
encoding algorithms used for other components of the servo wedge as will be discussed.
For example, servo synch mark detection circuit
69 may be an application
specific integrated circuit (ASIC) or other suitable type of circuit. Further,
microprocessor
84 may pre-program the servo synch mark detection circuit
69 and/or initialize the servo synch mark detection circuit with initial
and operational values to perform servo synchronization validation techniques based
on servo synch marks that conflict with self-clocking encoding algorithms. Although
the servo synch mark detection circuit
69 is shown as part of the read/write
channel
68, it should be appreciated that it may be located elsewhere in
the disk drive
30.
Host initiated operations for reading and writing data in disk drive
30
are executed under control of microprocessor
84 connected to the controllers
and memory arrays via a bus
86. Program code executed by microprocessor
84 is stored in non-volatile memory
106 and random access memory
RAM
108. Program overlay code stored on reserved tracks of disks
46
may also be loaded into RAM
108 as required for execution.
During disk read and write operations, data transferred by preamplifier
42
is encoded and decoded by read/write channel
68. During read operations,
channel
68 decodes data into digital bits transferred on an NRZ bus
96
to HIDC
74. During write operations, HIDC provides digital data over the
NRZ bus to channel
68 which encodes the data prior to its transmittal to
preamplifier
42. Preferably, channel
68 employs PRML (partial response
maximum likelihood) coding techniques, although the invention may be practiced
with equal advantage using other coding processes.
HIDC
74 comprises a disk controller
80 for formatting and providing
error detection and correction of disk data, a host interface controller
76
for responding to commands from host
36, and a buffer controller
78
for storing data which is transferred between disks
46 and host
36.
Collectively the controllers in HIDC
74 provide automated functions which
assist microprocessor
84 in controlling disk operations.
A servo controller
98 provides an interface between microprocessor
84
and actuator assembly
40 and spindle motor
50. Microprocessor
84
commands logic in servo controller
98 to position actuator
40 using
a VCM driver
102 and to precisely control the rotation of spindle motor
50 with a spindle motor driver
103.
Preferably, disk drive
30 employs a sampled servo system in which
equally spaced servo wedge sectors (sometimes termed "servo wedges") are recorded
on each track of each disk
46. Data sectors are recorded in the intervals
between servo sectors on each track. Servo sectors are sampled at regular intervals
to provide servo position information to microprocessor
84. Servo sectors
are received by channel
68, and are processed by servo controller
98
to provide position information to microprocessor
84 via bus
86.
Further, as previously discussed, read/write channel
68 may include a servo
synch mark detection circuit
69, which under the control of a program or
routine, may execute methods or processes in accordance with embodiments of the
invention to perform servo synchronization.
With reference also to FIG. 4, FIG. 4 shows a disk
402 of a disk drive
having a plurality of concentric tracks, and more particularly, illustrates a servo
synch mark (SSM) that conflicts with the self-clocking encoding algorithm of the
other components of the servo wedge, according to one embodiment of the present
invention. The disk
402 includes a plurality of concentric circumferential
tracks
422. Each circumferential track
422 includes a plurality of
embedded servo wedges
424 utilized in track following. The plurality of
servo wedges
424 are spaced sequentially around a circumference of the circumferential
track
422. For example, the embedded servo wedges
424a,
424b,
etc., contain servo information utilized in track following and are interspersed
between data regions
425 of the disk
402. Data is conventionally
written in the data regions
425 in a plurality of discrete data sectors.
Each data region
425 is typically preceded by a servo wedge
424.
Each servo wedge
424 includes a phase lock loop (PLL) field
428,
a servo synch mark (SSM) field
430 having an SSM that includes a pattern
that conflicts with self-clocking encoding algorithms, a track identification (TKID)
field
432, a wedge identifier (ID)
436, and a group of servo bursts
(e.g. ABCD)
438 (e.g. an alternating pattern of magnetic transitions) that
the servo control system samples to align the moveable transducer head with, and
relative to, a particular track.
The TKID
432, wedge ID
436, and servo bursts
438, in one
embodiment, have encoded patterns in accordance with a self-clocking encoding algorithm,
such as Manchester encoding, whereas the pattern of the SSM
430 is encoded
with an algorithm that conflicts with self-clocking encoding algorithms, such as
Manchester encoding.
Typically, the servo controller
98 moves the transducer head
64
toward a desired track during a coarse "seek" mode using the TKID field
432
as a control input. However, in processing information, it is necessary to ensure
consistency in the detection of bits composing a block of bits. In order to ensure
such consistency, the phase lock loop (PLL) field
428 is first read in order
to facilitate bit synchronization. Next, the servo synch mark
430 is read
to facilitate block synchronization. The SSM
430 facilitates block synchronization
by acting as a special marker that is detected to "frame" data, i.e., to identify
a boundary of a block. A valid servo synchronization signal results in the read/write
channel
68 of the disk drive
30 establishing a precise timing reference
point for read/write operations. It is well known to provide framing of servo data
via a SSM
430. The wedge ID
436 is a binary encoded wedge ID number
to identify the wedge.
Further, it should be noted that once the transducer head
64 is generally
over a desired track
422, the servo controller
98 uses the servo
bursts (e.g. ABCD)
438 to keep the transducer head
64 over the track
in a find "track follow" mode. During track following mode, the moveable transducer
head
64 repeatedly reads the wedge ID
436 of each successive servo
wedge
427 to obtain the binary encoded wedge ID (e.g. encoded in accordance
with Manchester encoding) number that identifies each wedge of the track. In this
way, the servo controller
98 continuously knows where the head
64
is relative to the disk
402. In one example, a disk track
422 may
have 256 wedges (e.g. 0-255) and may have a corresponding binary encoded wedge
ID number (e.g. 00000000-11111111). Of course, it should be appreciated, that the
disk may have any number of servo wedges and may utilize a wide variety of different
encoding schemes.
As previously discussed, a valid servo synchronization signal, based on the head
reading a SSM, typically causes the read/write channel
68 to establish a
precise timing reference point for read/write operations. Thus, it is important
that the servo synchronization signal be robust and timely.
In one embodiment, the present invention relates to servo synchronization techniques
based on an SSM having a pattern which conflicts with patterns utilizing self-clocking
encoding algorithms that are used by other components of the servo wedge. For example,
the TKID
432, wedge ID
436, and servo bursts
438 may have
patterns that are encoded in accordance with Manchester encoding, a type of self-clocking
encoding algorithm.
In one particular embodiment, the TKID
432 is encoded in accordance with
a self-clocking encoding algorithm whereas the SSM
430 is encoded in accordance
with a second algorithm that conflicts with the self-clocking encoding algorithm
of the TKID. In this way, the SSM
430 is prevented from being decoded as
a portion of the TKID
432.
More particularly, in one embodiment, the read/write channel
68 may include
a synch mark detection circuit
69. The synch mark detection circuit
69
may include a synch mark detection mode in which the synch mark detection circuit
69 validates a servo synchronization signal based on the head
64
detecting an encoded pattern of the SSM
430 that conflicts with the self-clocking
encoding algorithm of the TKID
432. The synch mark detection circuit
69
typically reads an encoded pattern of the SSM
430 and decodes the encoded
pattern of the SSM.
However, in one embodiment, the encoded pattern of the SSM
430 does
not comply with a self-clocking encoding algorithm, such as Manchester encoding,
whereas the rest of the components of the servo wedge such as the TKID
432,
wedge ID
436, and servo bursts
438 comply with a self-clocking encoding
algorithm, such as Manchester encoding.
For example, the servo synch mark detection circuit
69, under the control
of a program or routine, may execute methods or processes in accordance with the
embodiments of the invention to perform servo synchronization based on the detection
of SSM's
430 that conflict with self-clocking encoding algorithms, such
as Manchester encoding.
As will be discussed, in one embodiment, the synch mark detection circuit
69
may include a matched filter to match the encoded pattern of an SSM
430
with a SSM validation pattern in order to validate the servo synchronization signal.
Further, the read/write channel
68 may decode encoded patterns of the TKID
432, wedge ID
436, servo bursts
438, which are encoded with
self-clocking encoding algorithms, such as Manchester encoding.
Thus, in one embodiment, the self-clocking encoding algorithm of the TKID
432
is compatible with a Manchester encoding scheme whereas the encoding algorithm
of the SSM
430 conflicts with the Manchester encoding scheme. Moreover,
as previously discussed, other components of the servo wedge such as the wedge
ID
436 and the servo bursts
438, as well as other components, may
also utilize a self-clocking Manchester encoding algorithm. Also, it should be
appreciated that the SSM
430 may or may not be located adjacent to the TKID
432 and that other arrangements of the components of the servo wedge may
be utilized.
Turning now to FIG. 5, FIG. 5 is a diagram illustrating an example of an
SSM pattern that conflicts with self-clocking encoding algorithms, such as the
self-clocking Manchester encoding algorithm, typically used in RMSD's. Particularly,
FIG. 5 illustrates a pattern
502 recorded on the disk mainly in accordance
with the Manchester encoding algorithm representing values that may be received
by the read/write channel from reading servo wedges and data wedges, but in the
midst of this pattern
502, is a SSM pattern that conflicts with the self-clocking
Manchester encoding algorithm.
More particularly, pattern
504, as seen in FIG. 5, may consist of a plurality
of all "0's", (e.g. 0 0 0 0) or a plurality of all "1's" (e.g. 1 1 1 1). This SSM
pattern
504 recorded on the disk is not self-clocking and therefore conflicts
with self-clocking encoding algorithms. The dashed lines represent the read-back
signal generated by the head of the disk drive, which is fed to the read-write
channel, as it reads the encoded pattern.
For example, the read/write channel may decode a data pattern
506 that
it receives including a pre-qualifier, and primarily Manchester encoded data
508.
However, in the middle of the Manchester encoded data
508, is an SSM having
a pattern
510, that conflicts with the self-clocking Manchester encoding algorithm.
Based on this, as previously discussed, the synch mark detection circuit will
validate a servo synchronization signal based on the head detecting the encoded
pattern
510 of the SSM that conflicts with the self-clocking Manchester
encoding algorithm of the rest of the pattern
508, which may also include
the TKID, the wedge ID, servo bursts, etc. The synch mark detection circuit typically
reads the encoded pattern of the SSM and decodes the encoded pattern of the SSM
and verifies that it conflicts with the self-clocking encoding algorithm (e.g.
Manchester) of the other components of the servo wedge.
Now turning to FIG. 6, FIG. 6 is a flow chart of a method
600 of the invention
for implementing servo synchronization techniques based on a servo synch mark (SSM)
that conflicts with self-clocking encoding algorithms. At step
610, the
method
600, implementable, for example, by a synch mark detection circuit,
monitors for an SSM that conflicts with a self-clocking encoding algorithm (e.g.
a Manchester encoding algorithm). Next, at step
615, it is determined whether
a conflicting SSM pattern has been detected. If not, continued monitoring (step
620) is performed.
However, if an SSM that conflicts with a self-clocking encoding algorithm
is detected, then the SSM pattern is validated (block
630) and it is declared
that a valid SSM has been found (block
635). Thus, the servo synchronization
signal has been validated.
Turning now to FIG. 7, an example of a circuit that may be used in the synch
mark detection circuit is illustrated. In one embodiment, the circuit
700
of the synch mark detection circuit may be utilized to detect an encoded pattern
of the SSM that conflicts with a self-clocking encoding algorithm, and further
may match the SSM with an SSM validation pattern, in order to further validate
the SSM.
For example, a stream of data including SSM
430, TKID
432, wedge
ID
436, and other data is fed through the circuit
700. The stream
of data may first be processed by an analog-to-digital converter (ADC)
701
to digitize the signal. Next, the stream of data is fed through a Manchester decoding
circuit
702. The Manchester decoding circuit
702 decodes patterns
that are encoded in accordance with a Manchester encoding algorithm (i.e. a self-clocking
encoding algorithm). If the patterns are Manchester encoded, then they are decoded
by the Manchester decoding circuit, and continue on through the read/write channel
and to the rest of the RMSD for further processing. As shown in FIG. 7, the TKID
432, wedge ID
436, along with other data, are decoded by the Manchester
decoding circuit
702 and are passed on for further processing.
However, because SSM
430 conflicts with the self-clocking Manchester
encoding algorithm, it cannot be decoded by the Manchester decoding circuit. The
SSM
430 is therefore detected as not complying with the Manchester encoding
algorithm and may be further passed on to a matched filter
704 for further
validation. In this way, the SSM is prevented from being decoded as a portion of
the TKID.
In one embodiment, the matched filter
704 may be utilized to match the
encoded pattern of the SSM with a SSM validation pattern in order to further validate
the SSM. If the encoded pattern of the SSM is matched by the matched filter with
a pre-defined SSM validation pattern, then the SSM is validated and declared as
a valid SSM. In this way, the servo synchronization signal is verified. If the
SSM is not validated, it may be discarded as an invalid pattern.
For example, it should be appreciated that a series of 0's or 1's, as previously
discussed, may be utilized as the SSM validation pattern in the matched filter.
The SSM pattern may be of any suitable length so long as it conflicts with self-clocking
encoding algorithms, such as Manchester encoding. Additionally, it should be appreciated
that a wide variety of other different types of circuits to achieve this purpose
should be apparent to those of skill in this art.
By performing servo synchronization based on detecting an SSM that conflicts
with
self-clocking encoding algorithms, such as Manchester encoding, which is utilized
by the other components of the servo wedge, the chance of incorrectly validating
a servo synchronization signal due to it being misrecognized as one of the other
components of the servo wedge is significantly reduced. This is important because
if an SSM pattern is misrecognized as another area of the servo wedge, read/write
operations may be compromised resulting in the wrong data being read or data being
written to areas of the disk that is not supposed to be.
The methods previously discussed can be employed for disk drives with an embedded
servo system. However, numerous alternatives for RMSD's with similar or other media
format characteristics can be employed by those skilled in the art to use the invention
with equal advantage to implement these servo synchronization techniques. Further,
although the embodiments have been described in the context of a disk drive with
embedded servo sectors, the invention can be employed in many different types of
RMSD's having a head actuator that scans the media.
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