Control of servo timing mark detection windows

Details Control of servo timing mark detection windows Control of servo timing mark detection windows

1998-12-29

2001-01-16

Kim, W. Chris (Department: 2753)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data clocking

C360S053000, C360S063000, C360S077080

Reexamination Certificate

active

06175458

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to the field of disk systems, and in particular, to a system that controls a servo timing mark detection window.
2. Statement of the Problem
FIG. 1
depicts a current disk drive that includes a disk device
100
and a disk drive processing system
130
. Those skilled in the art are aware that numerous conventional aspects of the disk drive are not shown for clarity. The center of the disks
101
-
102
are each attached to a perpendicular spindle
107
. A spin motor
108
spins the spindle
107
and the disks
101
-
102
at a constant rate. The heads
103
-
106
read information that is stored on the disks
101
-
102
. The heads
103
-
106
pass signals containing this information to a pre-amp
120
. The pre-amp
120
passes only one of the signals from a selected head to the read channel
121
where the signal is processed into a format suitable for a processor
131
. The processed signal (or signals) is then passed to the processor
131
in the disk drive processing system
130
. The processor
131
executes firmware stored in the memory
134
to control the operation of the disk drive. This includes positioning the heads
103
-
106
relative to the disks
101
-
102
and exchanging user information with the disks
101
-
102
. The processor
131
and memory
134
could be a single integrated circuit or a group of integrated circuits.
The disks
101
-
102
each contain circular tracks that store both servo data and user data. The servo data includes position information that allows the disk drive processing system
130
to identify locations on the disks
101
-
102
. The servo data is uniformly spaced around the tracks of the disk, so that the heads
103
-
106
regularly encounter servo data as the disks
101
-
102
spin. Thus, the servo data is read at regularly spaced time intervals based on the constant spinning rate and uniform placement around the disk.
The servo data contains servo timing marks (STMs). STMs are used to locate and identify the corresponding servo data. An example of an STM may be no magnetic transitions on the disk for 350 nanoseconds followed by one magnetic transition followed by no magnetic transitions for another 350 nanoseconds. Each STM must be detected during a period of time known as a STM detection window that is generated by the disk drive processing system
130
. The STM detection window prevents false STM detection in cases where user data has similar characteristics to the STM. False STM detection can cause a catastrophic failure of the disk drive. The processor
131
may be used to detect the STM during the STM detection window, or additional circuitry (hardware) may be used for STM detection.
The processor
131
opens and closes the STM detection window by using the hardware timers
132
-
133
.
FIG. 2
illustrates this process. The processor
131
starts the hardware timer
132
when the first STM is detected in the signal. When the hardware timer
132
expires, the STM detection window opens for detection of the second STM. The false STM located before the STM detection window opens is ignored. The second STM is used by the disk drive processing system
130
since it is detected while the STM detection window is open. The processor
131
starts the hardware timer
133
at the opening of the STM detection window, and the STM detection window closes when the hardware timer
133
expires. The false STM located after the STM detection window closes is ignored.
Head switch operations add complexity to STM detection. During a head switch operation, the pre-amplifier
120
switches the signal that it passes to the disk drive processing system
130
. For example, the pre-amplifier
120
might pass a signal from the head
103
before the head switch and pass a signal from the head
106
after the head switch. It should be appreciated that during a head switch operation, the processor
131
must detect successive STMs in two different signals.
FIG. 3
depicts the head switch problem. The first STM may come from the head
103
signal, and after a head switch, the second STM may come from the head
106
signal. Physical mis-alignment between the heads
103
and
106
can cause timing misalignment between the first and second STMs as shown in FIG.
3
. In this case, the hardware timers
132
-
133
may fail to keep the STM detection window open until the second STM is detected. On
FIG. 3
, the legitimate second STM would be ignored since it is detected after the STM detection window closes. A failure to detect the STM requires a recovery procedure before normal operation can resume.
Mis-alignment is caused by thermal warping in mechanical assemblies or disk slippage from physical shock or handling. Removable media drives pose additional alignment problems. The servo data on removable disks is written by equipment that has different mechanical alignment than the actual disk drive used to read and write to the removable disks.
The current solution to this problem is to simultaneously reduce the length of the hardware timer
132
and increase the length of the hardware timer
133
during a head switch operation. This lengthens the STM detection window during a head switch operation to account for some mis-alignment. Unfortunately, the maximum length of the increase for hardware timer
133
must be estimated and fixed during the design of the hardware in the disk drive processing system
130
. If this design does not provide the proper amount of additional time, STM detection might fail during head switch operations where severe misalignment is present.
The normal duration of an STM detection window is 2-6 microseconds. This is typically increased to 20 microseconds during a head switch operation. Since the STM detection window is centered around the expected moment of STM detection, the STM detection window has 10 microseconds before and after the expected detection time point. Unfortunately, STM shifts of 50 microseconds or more can occur due to severe misalignment during head switch operations, especially with removable media drives. Redesigning the disk drive processing system
130
to increase the length of hardware timer
133
would be costly and impractical.
SUMMARY OF THE SOLUTION
The invention solves the above problem with a disk drive processing system that controls a Servo Timing Mark (STM) detection window during a head switch operation. In response to the head switch operation, the system disables the hardware timer that closes the STM detection window during normal operation, and the system tracks the elapsed time from a time point. The system compares the elapsed time to a programmable limit value. The system resumes normal operation if an STM is detected before the elapsed time reaches the programmable limit value and initiates a recovery procedure if the elapsed time reaches the programmable limit value.
The invention is advantageous because the limit value is programmable and is not limited by hardware since measurement of elapsed time is typically implemented in software and can span times much longer than the 50 microsecond or more STM timing mis-alignment during head switch operations. If severe mis-alignment is encountered during head switch operations, then the limit value can be increased to provide an STM detection window of the appropriate length. In contrast, the prior art system might be able to re-program hardware timers with new values, but these values would be unacceptably limited because of the fixed hardware design. A replacement of hardware would be required or the timers would need to be designed with numerous timer length selections. Both of these solutions are more complex and expensive than the present invention.


REFERENCES:
patent: 6067206 (2000-05-01), Hull et al.

Affiliated with

Also associated with

Rating

Control of servo timing mark detection windows does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Control of servo timing mark detection windows, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control of servo timing mark detection windows will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2461959