Disc drive power-up process including head mapping

Details Disc drive power-up process including head mapping Disc drive power-up process including head mapping

2000-04-20

2003-10-21

Deb, Anjan K. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S527000, C714S006130, C360S069000

Reexamination Certificate

active

06636049

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a power-up process for a disc drive, and particularly to a power-up process that includes mapping a logical-to-physical head map upon each power-up of the disc drive.
BACKGROUND OF THE INVENTION
Disc drives employ one or more recording discs to which data are written and from which data are read. A read/write transducing head is arranged to fly a design distance from each recording surface. In the case of a magnetic disc drive, each disc has two recording surfaces, so the disc drive will contain twice as many read/write heads as there are recording discs. Thus, a magnetic disc drive containing a two discs will contain four read/write heads, one for each of the four recording surfaces.
During manufacture, a head/disc unit is assembled containing a stack of magnetic recording discs mounted to a spindle motor in a housing, with an E-block rotatably mounted in the housing for operation by an actuator motor. The read/write transducing heads are mounted at the distal ends of actuator arms of the E-block and are arranged to “fly” a design distance from the confronting surface of the respective magnetic disc as the spindle motor rotates the disc stack. Prior to the present invention, the head/disc unit was then tested by writing test data onto each disc surface and reading that test data with the respective read/write head. If one or more heads fail to properly read test data from the confronting disc surface, that head/disc was considered “bad” and not available for future use. A logical-to-physical map was built to correlate the good heads to logical heads. The map was stored in the disc drive controller for use during operation of the disc drive. The disc drive was assigned a serial number that reflected the number of “good” head/disc interfaces, and was supplied to the market as a disc drive with some lesser number of disc surfaces. For example, if the drive held two disc and one head was “bad”, the drive was assigned a serial number and marketed as a three-surface disc drive.
The map created during manufacture associated the good physical heads to a logical head number. The logical head number commenced with zero. Hence, for a disc drive with four heads, the logical heads were numbered
0
to
3
. If, during manufacture, one of the heads was identified as “bad”, the map would assign the highest logical head number as “idle” and assign a logical number between
0
and
2
to the three “good” heads. For example, if physical head
3
is “bad”, the logical-to-physical head map would correlate physical heads
1
,
2
and
4
to logical heads
0
,
1
and
2
, respectively.
The controller associated with prior disc drives would, upon start-up of the disc drive, default to the zero logical head, which is, in the example, “good” head
1
. As the controller sequenced through the head, the map would note logical head
3
as idle, instructing the controller to sequence directly from logical head
2
(physical head
4
) to logical head
0
(physical head
1
). Similarly, the controller will directly sequence from physical head
2
(logical head
1
) to physical head
4
(logical head
3
) without attempting to read from bad physical head
3
.
At start-up, the controller performs certain start-up routines, including testing and adjusting the bias currents for magnetoresistive (MR) read heads. If the controller detects that the physical head assigned logical head number
0
is not operating correctly, the controller would attempt corrective actions, such as adjusting the bias current for the head or the head position in relation to a data track. If those corrective actions are not effective to correct the head, the controller continues to retry corrective actions indefinitely, until the problem is solved. However, if the physical head assigned logical head zero is defective, the controller can become stalled on the “bad” head.
Hearn et al., in U.S. Pat. No. 5,216,655, attempts to overcome the problem of controller stall by copying the head map to a specific location on each disc surface, or at least the disc surfaces associated with the “good” heads. The redundancy of the information on each disc ensures that if the controller becomes stalled on a given head/disc interface, the head map table will be available for access by the controller. However, upon start-up of the disc drive, the controller must default to one of the logical heads. The Hearn et al. map assumes that all of the physical heads corresponding to logical heads are “good”, so that as the controller defaults to one of the heads, it is presumed “good” and the head map is presumed to be accessible. However, if that default head is not good, the controller can not read the head map table. As a result, the controller either stalls as in the prior art, or selects a different head to retrieve the head map table from a different disc surface. Even if the controller of the Hearn et al. disc drive retrieves the head/map table from a different disc, the retrieved table is inherently defective since it assigns a logical head number to the bad head. This means that when advancing through the logical head sequence, the controller necessarily wastes effort with the bad head every time on start-up.
One problem associated with the Hearn et al. approach is that the head map table is fixed at manufacture and cannot adjust to environmental conditions, including age, that might deteriorate head differently. Should the head associated with logical head zero of the Hearn et al. become defective, the Hearn et al. controller may stall on the defective head and be subject to the same problems as the prior art disc drives.
The present invention addresses these and other problems, and offers other advantages over the prior art. More particularly, the present invention provides a start-up process by which the heads are mapped on each start-up, assuring that all logical heads of the head map table relate to “good” physical heads. Consequently, as the controller defaults to logical head zero, the controller is assured that a “good” physical head is accessed.
SUMMARY OF THE INVENTION
The present invention is directed to a power-up process for a disc drive that has a plurality of disc surfaces and a plurality of read heads confronting respective ones of the disc surfaces. Power is supplied to the disc drive spindle motor to rotate the plurality of disc surfaces and to the controller. A bias current is supplied to each read head to derive a voltage across the respective read head based on the supplied bias current and a characteristic of the read head. A level of operability of each read head is identified based on the voltage. A logical-to-physical head table is created that correlates the physical read heads to logical read heads based on head operability. The table is then stored in the controller memory. The logical-to-physical table is then used to perform read operations with the read heads by addressing the logical read head addresses in the table.
In embodiment of the process, each read head is iteratively selected, with the bias current being supplied to the read head and the level of operability identified during the respective iteration.
In another embodiment of the process, a representation of the voltage across the head is stored in a fault register. The representation in the fault register is compared to a threshold, and the fault identification is based on the stored fault.
In another embodiment of the invention, a logical-to-physical head map is defined based on a number of logical heads in the disc drive. The fault identification is stored for each head during its respective iteration. Upon completion of the sequence of iterations, the head map is defined using the stored fault identifications.
In one form of the invention a logical-to-physical head map for a disc drive is built upon power up of the disc drive. Power to the disc drive operates the disc drive spindle motor to rotate the plurality of disc surfaces and operates the controller. The read heads are iteratively selected to supply a bias

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