Dynamic magnetic information storage or retrieval – General processing of a digital signal – Address coding
Reexamination Certificate
1999-12-20
2002-09-03
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Address coding
C360S031000
Reexamination Certificate
active
06445524
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a method of operating a disk drive for writing to an addressable location after detecting that a head is within a safe-to-write window.
2. Description of the Prior Art
A disk drive has a control system generally comprising an interface microprocessor, which directs the activities of the disk drive, and a servo microprocessor, which controls the position of a read/write head. The interface and servo functions may be embodied in a single microprocessor or in separate microprocessors. A disk controller or formatter circuit automates disk data transfer functions such as reading and writing data sectors under control of the interface microprocessor. An exemplary such disk drive is shown in commonly assigned U.S. Pat. No. 5,965,992 to Goretzki et al which is hereby incorporated by reference.
During a write operation initiated by a host computer, a disk drive receives a sequential series or “string” of data blocks from the host. The string of data blocks is stored in a disk memory buffer for writing to corresponding addressable locations on a data track of a disk. Each addressable location may be a structure on the track known as a data sector, conventionally referenced by a logical block address (LBA). The control system of the disk drive requires that the read/write head be positioned over the track and that the head follow the track to within a tolerance limit during the entire write operation. When the head is positioned within the tolerance limit, the head is said to be within a safe-to-write window. If the head wanders off-track or outside the tolerance limit for whatever reason during a write operation, the head is declared to be outside the safe-to-write window by the control system and the write operation must stop to avoid overwriting data on an adjacent track or tracks. One reason the head may wander off-track is that the drive may have been subjected to a shock impulse. Conventionally, to recover from such a shock event, the disk drive control system will wait until the head is once again following the track within the tolerance limits and the first addressable location corresponding to the string passes under the head on a subsequent revolution of the disk before attempting to re-write the string of data blocks. The control system will therefore wait until the appropriate servo wedge preceding the first data block to be written passes under the head to verify track following within tolerance levels before attempting the write operation again.
It should be understood for this discussion that the disk drive head conventionally comprises an integration of separate read/write elements in a fixed relationship such that the read element provides position information to the servo controller and the servo controller uses the position information to position the head to place the write element on track for writing.
FIG. 1
is a timing diagram of a write operation in a prior art disk drive in the presence of a condition causing the head to wander outside a safe-to-write window.
FIG. 1
is divided into an upper and a lower portion. The upper portion illustrates sequences of events occurring during a first pass of the addressable locations under the head, whereas the lower portion thereof illustrates the sequence of events occurring during a second pass of the addressable locations under the head. Bold arrows
102
and
104
indicate the length of time the write operation is pending during the first and second passes respectively. A disk track
150
, as shown in
FIG. 1
, includes a plurality of addressable locations D
1
-D
12
corresponding to a string of logical data blocks D
1
-D
12
, received from a host for writing, and embedded servo sectors or “wedges” S
1
-S
3
interspersed there between. The servo wedges are read by the head and used by the control system to determine the head's most recent position on the disk. As the head positioning system is a sampled system, the precise position of the head is unknown until a servo wedge is read and the position information stored therein is processed. As shown in
FIG. 1
, a disk controller command (Write D
1
-D
12
) is issued by a system control microprocessor to cause the head to write data blocks D
1
through D
12
on the track
150
from a buffer memory. As the media is rotating, the disk controller has an opportunity to write the data blocks D
1
-D
12
during a “pass” of the string of data blocks D
1
-D
12
under the head. The pass is initiated by the addressable location D
1
passing under the head. The pass is terminated when the addressable location D
12
passes under the head. In the illustration of
FIG. 1
, the shaded addressable locations have been written, whereas those that are not shaded have yet to be written to disk. During the writing of data block D
2
, a signal (safe-to-write) asserting a safe-to-write-condition is de-asserted, indicating that it is no longer safe to write to the disk. The safe-to-write signal is a signal that is transmitted by the servo controller and if de-asserted may cause the write operation to be immediately aborted. The safe-to-write signal may be de-asserted for a variety of reasons, and generally indicates a temporary condition that may disappear over time.
A shock event is one such temporary condition. During the shock event, the head may have wandered outside a safe-to-write window, increasing the likelihood that data on adjacent tracks may be inadvertently overwritten. After reading the servo wedge S
2
and determining that the head is now back on the desired track or within the tolerance limit, the safe-to-write signal is re-asserted. There is some latency between the reading of the servo wedge S
2
and the reassertion of the safe-to-write signal as the head passes over data sector D
6
, as some processing time is required to determine the position of the head. Although the diagram of
FIG. 1
shows the safe-to-write signal being re-asserted immediately following servo wedge S
2
for illustration of the concept, actual practice would dictate that the safe-to-write condition be tested repeatedly until some number of servo wedges have been read in succession to verify that the read/write head is staying within the safe-to-write window.
The writing of the data blocks, as shown in the upper portion of
FIG. 1
, stopped after writing D
2
. As shown in the lower portion of prior art
FIG. 1
, the disk drive control system refrains from writing any data blocks until another pass is initiated. In this case, the next pass is labeled as second pass. As whatever event caused the servo controller to de-assert a safe-to-write condition occurred at some indeterminate time prior to servo wedge S
1
, the servo controller (after the safe-to-write condition is restored at some time after S
2
during the first pass) backs up and re-writes the entire string of data blocks D
1
-D
12
, as shown in the lower portion of FIG.
1
. In practice, the head may be commanded to back up a predetermined number of blocks (as measured from the servo wedge at which it was determined that the head has wandered off-track) before rewriting all or a portion of the string of data blocks, as a precautionary measure. Therefore, according to the prior art disk drive operating method, at least two revolutions of the disk or one revolution plus the time for the complete string of blocks D
1
-D
12
to pass under the head during second pass
104
are necessary to complete the write operation. In this illustration, the summed length of arrowed lines labeled
102
and
104
indicates the relative length of time required to complete the operation.
Original Equipment Manufacturers (OEM's) of disk-drive-containing systems often specify disk drive performance requirements that must be met by disk drive manufacturers. Such requirements often specify the maximum data transfer performance degradation that is allowed as the drives are subjected to and recover from an event (such as
Codilian Raffi
Nazarian Ara W.
Hudspeth David
Kapadia Varsha
Shara, Esq. Milad G
Western Digital Technologies Inc.
LandOfFree
Method of operating a disk drive for writing to an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of operating a disk drive for writing to an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of operating a disk drive for writing to an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2829186