WO1991000594A1

WO1991000594A1 - Method for compensating for the unique mechanical and electrical characteristics of a disc drive

Info

Publication number: WO1991000594A1
Application number: PCT/US1990/003588
Authority: WO
Inventors: Don Michael Robinson
Original assignee: Seagate Technology, Inc.
Priority date: 1989-06-30
Filing date: 1990-06-29
Publication date: 1991-01-10

Abstract

A disc drive wherein at least two outer tracks of the disc in a region (15) beyond the defined track 0 are used to store the drive operating microprogram, and/or manufacturing test program, and/or specific electrical, mechanical and magnetic parameters and media defect information. This data can be read from these outer tracks of the disc during initialization of the disc drive, or during seek operations of the drive to immediately adjust the positioning of the read/write head. It allows the disc drive to react to microprogram problems without changing either the mask ROM or an EPROM supplied. The microprogram is read onto the drive over the I/O interface.

Description

METHOD FOR COMPENSATING FOR THE UNIQUE MECHANICAL AND ELECTRICAL CHARACTERISTICS OF λ DISC DRIVE

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of appli¬ cation Serial No. 800,062 filed November 20, 1985.

FIELD OF THE INVENTION This invention relates generally to magnetic disc memory apparatus and more particularly to means for improving performance of a disc drive by improved management of characteristics unique to an individual disc drive.

BACKGROUND OF THE INVENTION Disc drive systems record and reproduce data stored on concentric circular tracks recorded on magnetic discs. The tracks are written and read by a magnetic transducer that cooperates with the surface of the disc. The transducer is positioned over a selected track or cylinder on the disc by an actuator mechanism. Detailed disclosure of disc drive machines, and especially a typical linear actuator for positioning the transducers in alignment with a selected cylinder or track on the surface of a disc, is found in U.S.Patent 4,323,939; a rotary actuator incorporating a stepper motor for positioning a transducer is found in U.S. Application Serial No. 115,691, filed November 2, 1987. Both are incorporated herein by reference.

Disc drives, and especially the positioning devices, are microprocessor controlled. The microprograms typically provided for disc drive controllers are reguired to meet strict customer and 10 interface requirements. The inter¬ face requirements and the size of the programs require long development and test cycles before the programs can be committed to ROM or EPROM for production. Once the com- mitment has been made to put a program in ROM, it is difficult to correct any problems. Thus, products manu¬ factured in high volume, with microprograms stored in ROM memory, have high cost per engineering change which affect the ROMs, i.e., require scrapping the ROMs which have been previously manufactured.

Further, ROM/EPROM based products are difficult to cus¬ tomize for specific customer requirements, as each modi¬ fication to the program requires a new ROM or EPROM.

Another major problem with storing all the control infor¬ mation for a disc drive in ROM, is that manufacturing testing of such a product is difficult as all the test programs must be held within the ROM. Further, it makes defect management difficult and inefficient.

SUMMARY OF THE INVENTION It is em objective of this invention to provide improved means for storing some of the controlling operating data in a microprocessor controlled disc drive.

A further objective of this invention is to improve the system for controlling the data transducer in rotating disc data storage equipment.

Another objective herein is to improve the performance and reliability of rotating disc data storage devices while reducing its complexity and cost of manufacture.

A further objective is to increase the capacity of the rotating disc data storage device without increasing its complexity or cost of manufacture. Yet another objective is to provide an efficient approach to storing unique, magnetic, mechanical and electrical characteristics of a disc drive.

In known disc drive systems, any defective block on a track will cause the entire track to be flagged as defective. This results in a considerable loss of capacity. There¬ fore, a further objective herein is to bypass defects at a track sector level rather than a track level.

Yet another objective herein is to provide a rotating disc data storage device with internal means for dynamically storing a defect list at a sector level to enhance updating of the defective sector list of the device.

Another objective of this invention is to provide a means for storing a data list which may be comprised of both the manufacturer generated data defect list and a user supplied defect list. Such storage of a manufacturer's defect list in dynamic memory will allow it to be generated by special test equipment, saved on disc in a specially protected area, and accessed by the controller to directly bypass defects without unnecessary seeking steps. Such defect management approach also allows for a user supplied defect list to be added to the manufacturer's defect list, saved on the disc for future format operations and if necessary, removed on command.

Yet another objective herein is to provide a method for storing the electrical, mechanical and magnetic character¬ istics of a disc drive in dynamic memory on the drive, so that the performance of the drive is essentially customized to its individual characteristics.

These and other objectives are achieved in a disc drive wherein at least two outer tracks of the disc in a regio beyond the defined track 0 are used to store the drive operating microprogram, and/or manufacturing test program, and/or specific electrical, mechanical and magnetic para¬ meters and media defect information. This data can be read from these outer tracks of the disc during initiali¬ zation of the disc drive, or during seek operations of the drive to immediately adjust the positioning of the read/ write head. It allows the disc drive to react to micro¬ program problems without changing either the mask ROM or an EPROM supplied. The microprogram is read onto the drive over the I/O interface.

The product yield is also improved by this process as specific mechanical yield on electrical parameters can be adapted to by including these in the drive microprogram.

In a specific embodiment of this invention, the sector defect list is stored as supplied by the manufacturer on the outer track of the drive. If desired, it is merged with the user supplied defect during formatting and used during formatting to flag defective sectors. During initialization of the disc drive, the defect list is loaded into a section of dynamic memory so that it is quickly accessible during seeking of a particular address.

Thus, when a seek command is received, the defect list can be accessed, and the positioning command is modified to avoid accessing of a defective block, instead directly accessing the next effective block.

Further enhancements of the embodiment allow for reading data stored on disc and peculiar to a given drive as write current; thermal characteristics, i.e., expansion, incurred at differing operating temperatures; and trajectory and force constants of the servo systems, to produce more accurate positioning of the transducer over the target track. Such increased accuracy will allow reduction of the bandwidth separating adjacent tracks, and increase storage capacity.

As an example of modifying the mechanical characteristics of a disc drive, it is desirable to modify the write current depending on the target position of the transducer relative to given sectors or cylinders on the disc. Therefore, a table of write current values related to disc sector" locations^' may be stored on non-user accessible tracks on the disc surface and accessed in response to a command to write data at a particular cylinder or sector so that the most effective write current is used at all locations on a disc.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention can be better understood by reference to the following figures:

FIG 1 is a plan view of a disc drive with which this invention is useful; FIG 2 is a block diagram of the sequence of steps t be followed in addressing a particular sector on a dis drive track;

FIG 3 illustrates the arrangement of particula cylinders heads and sectors on a disc drive as in FIG 1. FIG 4 comprises a flow chart of a program for selec tively modifying the write current based on the location t be written.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A typical disc drive, as shown in FIG 1, includes a plural ity of discs 12 stacked on a spindle 25 for rotation by spindle motor. A transducer 10 is positioned over any o the tracks 0-685 for reading or writing data on the select ed track. The positioning occurs under control of a moto 30 (which may be a stepper or voice coil type) in respons to commands from a microprocessor 40. In this exemplar embodiment which uses a stepper motor, rotation of th stepper motor 30 and its spindle 36 causes a band 38 which is connected to the head 19 of the arm 32 to wind and unwind on the spindle 36, moving the arm 20 and associated transducer 10 to the selected track.

As an aid to understanding this invention that involves reading and writing on a specific track location, it should be understood that the following physical characteristics are typical of a disc drive and will be referred to in the explanation below: 615 cylinders (numbered 0-614) , four heads (tracks per cylinder, numbered 0-3) , 17 sectors per track (numbered 0-16), 512 data bytes per sector, 41,820 sectors per head (numbered 0-41819) .

Once the microprocessor is given the information as to the desired track sector which is to be accessed, it commands motor 30 to move the transducer 10 to the target cylinder. The proper head is then selected to access the targeted track and sector.

In addition, the drive has at least two additional cylinders which include some of the outermost tracks on the disc but which are non-user accessible and identified as the -1 and -2 .cylinders. In this example, where four transducers are provided, the cylinders include four tracks each, formatted 256 bytes per sector, 32 sectors per track and with a 1 to 1 interleave factor.

The object of this invention is to minimize the time spent in mechanically seeking for the correct track and sector, as well as maximizing positioning accuracy over that track. In general, this is accomplished by storing electrical, magnetic and mechanical characteristics as veil as a sector defect list on the non-user accessible tracks (tracks -1 and -2, discussed above). These characteristics and/or the defect list can be accessed either when the unit is first turned on, or when a seek is made, as desired. A specific example to be described below is how a defect list can be accessed for each seek. Other examples will then be considered, including modification of the write current on the basis of the data location to be accessed.

What shall be termed "improper seeking" herein can occur if the original seek of a transducer to a read/write location is carried out to a block or track which is defective. Such disc media block or track defects fall into two categories. One category comprises defects identified by the manufacturer during the course of testing, using stress enlarging techniques. These defects are supplied in a list in cylinder, head, and bytes from index formats. An example of the numbering scheme appears in FIG 3. The cylinder 0 is a reference to the fact that in a disc drive having multiple data storage surfaces on discs, track 0 on each disc is defined as lying on a single cylinder 0. A separate head or transducer 10 reads and writes the data on each disc surface. Therefore, a particular location in any disc surface may be particularly identified by defining the cylinder and the head number (these two together combining to identify a particular track on a particular disc surface) followed by identifying a particular sector.

Other defects which must be taken into account are those identified by the user over a period of time. These defects are supplied in a list in logical block address format. The defect information and operating systems and the like may be stored on a disc drive for ready access in the disc drive on tracts -1 and -2 identified above.

In order to make best use of the defect list, the follow¬ ing steps are taken:

First, the manufacturer generated defect list is converted into a physical cylinder, head, sector format to make up the known defect list. Second, the defective sectors are flagged so that they are functionally bypassed.

Third, a method is provided for the user to add de¬ fects to the known defect list using logical block address format. (It is well known in the disc drive field to convert logical block addresses into cylinder head and sector addresses as most seek commands are initially input as logical block addresses) .

Fourth, the added de ects are^~ converted t©^~ physical cylinder head sector format, taking into account previous defects and the interleave factor in the discs.

Fifth, the added defects are merged into the known defect list.

Finally, the logical block address is translated into cylinder head and sector addresses and adjusted for defects to avoid performance hits during seek.

Considering these steps in detail, the first step is the conversion of the manufacturer's defect list into a physi- cal cylinder, head, sector format. This becomes the Icnown defect list. This is done by taking the entry in the manufacturer's defect list and inserting cylinder and head into the known defect list and looking at the sector defect map to find the sector number(β) that contain a comparable range for the bytes from index number. When a sector number match is found, that number is added as an entry into the known defect list. The last number in the known defect list is a relative defect in the list with the first entry being 1, the second entry being 2, the third being 3, and so on. All of this technique is well known in this technology.

The entries in the sector defect map overlap to account for gaps and speed variations, so it is possible for one manufacturer's defect entry to become two entries in the known defect list. Basically, the objective is to provide a list of defects defined in terms of cylinder head and sector on the disc of a particular disc drive.

Next, the defective sectors are flagged so that they are functionally bypassed. During format unit operation, the disc is incrementally formatted a track at a time, start¬ ing at cylinder 0, track 0, to cylinder 614, track 3. The first sector on cylinder 0, track 0 is formatted as logical block 0. The logical block address is incremented across the entire disc and not reset to 0 on track or cylinder boundaries. Before formatting each track, a table with an entry for each physical sector on the track is generated. Referencing the known defect list, any defective sectors are marked defective. The remaining sectors are numbered taking into account the interleave factor. The defective sector does not get a logical block address and does not cause a logical block address to be skipped. It merely means one less logical block for each defect encountered. Thus, this step is basically an extension of known format- ting and sector addressing techniques, with the only modification being in the numbering scheme to take into account the defects which have been identified so that they are not given addresses and are not addressed during any data access command.

Next, the user can add defects to the Icnown defect list using logical block address format, simply by using the standard manual format commands which are well known in the disc drive industry.

Next, the added defects are converted to cylinder heads and sector format taking into account previous defects and the interleave factor. Thus, these are simply eliminated as possible addresses for data storage so that they are not reaccessed. Next, the added defects are merged with the known defect list into a scratch pad area, in the microprocessor 40, then copied back into the known defect list so that a single merged list is generated.

Now, when a read command that comprises a logical block address as in FIG 2 is received, it is converted into a cylinder head and sector address and adjusted for defects to avoid performance hits during seek time. In order to accomplish this, when the disc drive 15 is powered on, the known defect list is loaded into a RAM 41 which is part of MPU 40. (This way, when new defects are added by a format command by the user, the new known defect list is written back to the -2 cylinder, so the latest updated defect list is always available to upload at power on, and during operation is always available in the RAM 41.)

Read/write and seek commands are presented in logical block format to the microprocessor 40. In order to correctly position the actuator 32. and select the correct head 10, the logical block address is converted to target cylinder head and sector address at step 50. This alone would be enough information to correctly position the actuator head and select the correct head if there were no defects. The average seek time for such an operation is 65 milliseconds, with track time being 20 milliseconds. Be¬ cause the known defect list is available in RAM at all times, the computed cylinder head and sector can be accu¬ rately corrected for defects as shown in the following steps in approximately 70 microseconds. This avoids a 60 ms seek to a wrong track and a subsequent 20 ms to 65 ms reseek to the correct track and sector. Thus, by simply converting the incoming block address to cylinder head and sector address, and adjusting for defects, at 52, a seek to a correct cylinder and head is immediately achieved. For example, looking at the defective sector in FIG 3, without the benefits of this invention, a command to read sector 67 would have initially called for a βeek-to-cylin- der stroke; then, because the defective sector 67 is now on cylinder 1, a reseek would have had to occur to the correct cylinder. The time needed to carry out the reseek would have been list. Instead, an automatic adjustment is made to the correct seek address with no loss in performance.

Thus, following step 52, a seek to the correct cylinder and head position is immediately done and a read operation conducted at 56. If more blocks are to be transferred as shown at the decision block 58, the next block is converted to cylinder-head-sector format at step 60; the necessary cylinder or head switch is carried out at step 62; and a branch is carried out to select the correct head. Then the program returns to step 54 to cause the actuator to seek to the correct track address. If no cylinder or head switch is re-quired at step 62, the next block is immediately read at step 64 followed by a return to the command to wait for the end of the sector at 66 and then branching to the finish of the program.

In summary, by providing for an adjustment for defects on receipt of a block address from a user as part of a seek command, considerable time and performance is saved.

Further, an improvement is achieved over prior art methods in which an entire track had to be flagged as defective, with alternate data tracks being provided for storage of the data intended to be stored in the defective blocks on the now unused tracks. This alternative approach resulted in a considerable loss in capacity.

A similar approach to that described at length above can be used to store the basic electrical, mechanical and magnetic characteristics of the HDA on non-user accessible tracks -1 and -2 to facilitate the positioning of the transducer over a desired track. For example, by storing the magnetic characteristics, the disc media can be optimally matched with the read/write head in a given -disc.

The write current could be defined during testing of the HDA and stored on the non-accessible tracks. It could be accessed by the controller 40 which would then use that write current to set up the drive electronics for a par- ticular read/write head and surface in a disc drive. In an even more particular application, because of the storage capacity, the disc could be divided into bands each com¬ prising a plurality of cylinders with the write current stored on a per cylinder or per zone basis. An example of implementation of such a selective write current modifica¬ tion scheme is discussed below with reference to FIG 4.

The mechanical characteristics could also be adapted for an individual drive by storing trajectory and force con- stants of the servo system to create optimum trajectories for access to a given track. The disc drive would be divided into bands of cylinders, and the microprocessor 40 would access the trajectory and force data for optimally positioning the transducer over the desired track. This would increase yield on drives, and optimize spacing between adjacent tracks, maximizing the capacity of the disc drive.

To adapt a particular HDA to the stepper motor incorpo- rated therein, the stepper motor algorithm comprising the timing information for driving the stepper motor to perform the seek to a given track could also be stored on the non-user accessible tracks.

To adapt each disc drive for its unique thermal compensa¬ tion characteristics, the cold start characteristics and start-up modifications to the thermal characteristics could be stored, read and used to modify track positioning on the basis of the in-housing ambient temperature of the drive. That is, as the HDA heats up, it is known to go through a certain amount of distortion. This distortion can be ascertained during factory testing, and stored on the disc to be accessible during drive operation.

This approach could be implemented by storing a serial number for each drive on the disc as it moves through the assembly process. The defect map resulting from testing and the other characterization data realized during manu¬ facturing would be applied to that disc drive and stored on the non-user accessible tracks at the conclusion of the test process. Once this data is stored on tracks of the disc, it can be accessed and moved into random access memory each time the drive is started up or each time data is to be accessed. The write current could then be defined by setting bytes in a register controlling the current for the read/write heads. Thereafter, for each seek, the write current register could be read and updated based on the track or zone to be accessed.

The process of modifying the write current on the basis of the sector to be accessed can be better understood by reference to the flow chart of FIG 4.

The following terms should be understood in reviewing the flow chart. "Cylinder factor" means the cylinders per write current zone; "physical sector" means the number of data sectors from index in a given cylinder. The "sector factor" is the data sectors per track divided by the write current sectors per track. The "write current sector" is the sector boundary for write current switching. The write current zone is the cylinder range for write current values. The subroutine shown in FIG 4 is initiated with the receipt of each seek command. The subroutine begins with a calcu¬ lation at step 80 of the cylinder, head and physical sector at which the write is to be performed. This information is essentially contained in the seek instruction. Given this information, the calculation 82 can be performed which calculates the write current zone i.e., the cylinder divid¬ ed by the cylinder factor, the cylinder factor being a pre¬ determined constant. As a next step 84, the write current sector is calculated as the physical sector (calculated at step 80) divided by the sector factor which is also a pre- established constant.

Based on this information, the write current table index, which has been predefined for the disc drive and stored in memory (which may be a permanent memory such as a read-only memory) is accessed at step 86. This table is accessed as a function of the write current zone calculated at step 82, the head which is designated to access the data is a part of the seek instruction, step 80, and the write current sector which is calculated at step 84. The result of accessing this table index is to provide a write current value, step 88, which will be used to control the write current level used to write data at the defined cylinder and sector with a given head. Typically, it is stored in a defined section of RAM 41 which may be designated as a write current memory. The data to be written is then loaded in the drive register at step 90 and the information is written. The microprocessor 40, after writing each sector, queries to see if all sectors have now been written, step 92. If all sectors have been written, the subroutine ends, step 94. If further information remains to be written, the sector to be written is incremented, step 96, and the program returns to step 82 to recalculate the write current zone and write current sector values so that a new write current table index 86 can be generated. Alternatives to this invention may become apparent to a person of skill in the art who studies this invention disclosure. Therefore, the scope of this invention is to be limited only by the following claims.

Claims

WHAT IS CLAIMED:

1. In a disc drive with at least one disc, a trans¬ ducer for reading and writing data on said disc, and means for positioning said transducer relative to said disc, said positioning means being responsive to position commands to position said head relative to said disc, the improvement comprising means for storing disc drive characterization information on tracks of said disc outside the user accessible list of tracks, means for accessing said stored information and means for establishing operating charac- teristics of said drive based on said stored information.

2. A disc drive as in Claim 1 wherein said means for storing characterization information includes means for storing a defined write current level, and means for acces¬ sing said defined current level and using said stored defined write current to control the write current for writing data on said disc.

3. In a disc drive, a method of adjusting for the unique electrical, mechanical and/or magnetic characteris¬ tics of said disc drive assembly, said assembly including at least one disc having a plurality of storage tracks for storing information, a transducer for accessing said trans¬ ducer and driven by a motor for positioning said transducer over said disc, said disc having a user accessible list of tracks comprising less than all of the tracks on said disc for storing said information, and a non-user accessible list of tracks that are capable of storing said informa¬ tion, testing the disc drive assembly to define said unique characteristics, storing said characteristics on said non-user access- ible tracks, accessing said information prior to activating said motor to move said transducer to one of said user acces- βible tracks, whereby said transducer is accurately posi¬ tioned over one of said tracks.

4. A method as in Claim 3 wherein said disc surface is divided into a plurality of circumferential bands, εaid method including storing said characteristics for each of said bands, and accessing said stored characteristics before performing a seek into one of said bands.

5. λ method as in Claim 3 wherein said step of storing characteristic data includes storing a write current defined by the c-haracteristics of said transducer and said disc surface.

6. A method as in Claim 5 wherein said accessing step includes the step of moving said write current charac¬ teristic from said disc surface into a register, and acces¬ sing said register prior to each seek.

7. A method as in Claim 4 wherein said step of stor¬ ing characteristic data includes storing a write current defined by the characteristics of said transducer and said disc surface for each cylinder on said surface, and acces- sing the write current data prior to each seek on the basis of the cylinder to be accessed.

8. A method as in Claim 7 wherein said accessing step includes the step of moving said write current charac¬ teristic from said disc surface into a register, and acces¬ sing said register prior to each seek.

9. A method as in Claim 4 wherein said stored char¬ acteristics comprise storing trajectory and force constants relative of servo system for positioning said transducer over each of sand bands of tracks, and accessing said con- stant prior to positioning said transducer whereby differ- ent trajectories for seeks to different bands of tracks may be adopted.

10. A method as in Claim 4 wherein said step of storing characteristics comprises assigning a reference number to each disc drive during assembly, testing said disc drive to establish the characteristics of that drive, and storing an assigned mrite current value to reflect the construction of said drive.