# Patent

## Title
Data storage device writing a multi-sector codeword in segments over multiple disk revolutions

## Abstract

A data storage device is disclosed comprising a head actuated over a disk comprising a plurality of data sectors. During a first revolution of the disk, write data is first encoded into a codeword spanning at least a first data sector and a second data sector and a first part of the codeword is written to the first data sector. During a second revolution of the disk, the write data is second encoded into the codeword and a second part of the codeword is written to the second data sector.

## Background
CROSS REFERENCE TO RELATED APPLICATION(S)
This application claims the benefit of U.S. Provisional Application No. 61/931,805, filed on Jan. 27, 2014, which is hereby incorporated by reference in its entirety.


BACKGROUND
Data storage devices such as disk drives may comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
FIG. 1 shows a prior art disk format 2 as comprising a number of servo tracks 4 defined by servo sectors 60-6N recorded around the circumference of each servo track. Each servo sector 6i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6i further comprises groups of servo bursts 14 (e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts 14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a prior art disk format comprising a plurality of servo tracks defined by servo sectors.
FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head actuated over a disk.
FIG. 2B is a flow diagram according to an embodiment wherein during a first revolution of the disk a codeword spanning multiple data sectors is encoded and a first part written to the disk, and during a second revolution of the disk the codeword is encoded and a second part written to the disk.
FIG. 2C shows an example embodiment wherein a codeword is encoded three times and written to the disk over three revolutions.
FIG. 3A shows an embodiment wherein write data received from a host is stored in a buffer and then transferred to an encoder each time the codeword is encoded.
FIG. 3B shows an embodiment wherein a write gate is disabled during the write operation due to a detected off-track condition.



DETAILED DESCRIPTION
FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head 16 actuated over a disk 18 comprising a plurality of data sectors. The disk drive further comprises control circuitry 20 operable to execute the flow diagram of FIG. 2B, wherein a need to write data is triggered (e.g., write data is received from a host, a background process of the drive initiates a write), and during a first revolution of the disk (block 22), the write data is first encoded (block 24) into a codeword spanning at least a first data sector and a second data sector (e.g., FIG. 2C) and a first part of the codeword is written to the first data sector (block 26). During a second revolution of the disk (block 28), the write data is second encoded (block 30) into the codeword and a second part of the codeword is written to the second data sector (block 32).
In the embodiment of FIG. 2A, the disk 18 comprises servo tracks 34 defined by servo sectors 360-36N, wherein data tracks are defined relative to the servo tracks 34 at the same or different radial density. Each data track comprises a plurality of data sectors, wherein each data sector may store one or more host blocks of write data. The control circuitry 20 processes a read signal 38 emanating from the head 16 to demodulate the servo sectors 360-36N and generate a position error signal (PES) representing an error between the actual position of the head and a target position relative to a target track. The control circuitry 20 filters the PES using a suitable compensation filter to generate a control signal 40 applied to a voice coil motor (VCM) 42 which rotates an actuator arm 44 about a pivot in order to actuate the head 16 radially over the disk 18 in a direction that reduces the PES. The servo sectors 360-36N may comprise any suitable head position information, such as a track address for coarse positioning and servo bursts for fine positioning. The servo bursts may comprise any suitable pattern, such as an amplitude based servo pattern or a phase based servo pattern (FIG. 1).
In one embodiment, the write data received from the host is encoded using any suitable error correction code (ECC) capable of detecting and correcting errors during a read operation. The ECC may generate redundancy data over the write data, wherein the redundancy data may be stored with the write data during the write operation. Examples of a suitable ECC include an iterative code such as a low density parity check (LDPC) code which may be decoded using an iterative type decoder, or a polynomial code such as a Reed-Solomon (RS) code which may be decoded using a polynomial type decoder, or a combination of ECCs may be employed.
In one embodiment, an ECC codeword may be generated over multiple data sectors of a data track. For example, in one embodiment the ECC may employ interleaving wherein every nth data sector of a data track may be encoded into a corresponding codeword. Consider the example of a three-interleave encoder where every 3rd data sector may be encoded into a corresponding codeword, a first codeword may be generated over data sectors 1, 4, 7, a second codeword may be generated over data sectors 2, 5, 8, and a third codeword may be generated over data sectors 3, 6, 9. In one embodiment, interleaving the data sectors into multiple codewords improves the correction power of the ECC by spreading a long defect into two or more codewords. That is, each codeword may be capable of detecting and correcting a section of a long defect, whereas the same long defect may exceed the correction power of a single (non-interleaved) codeword. In the example shown in FIG. 2C, the codeword is shown as spanning multiple consecutive data sectors; however, the data sectors of a codeword may not be consecutive as in the above-described interleaving embodiment.
When writing the data sectors of a codeword to the data track during a write operation, the write operation may need to be interrupted due, for example, to a detected off-track condition, a sagging power supply, an accelerometer detecting a free-fall condition, or any other suitable reason. For example, the control circuitry 20 may include a vibration sensor capable of sensing a vibration that may cause the head 16 to deviate from the data track. In another embodiment, the control circuitry 20 may detect an off-track condition by evaluating the PES generated when reading the servo sectors in the data track. When an off-track condition is detected, the write operation may be aborted for the current revolution, or the write operation may be paused until the control circuitry 20 detects that the head 16 is again on-track. Whether the write operation is aborted or paused during a first revolution of the disk, at least one data sector of a codeword may be skipped during the first revolution (e.g., data sectors 2, 3 and 5 of FIG. 2C). During a second revolution of the disk, the control circuitry 20 may skip the previously written data sectors and attempt to write the previously skipped data sectors (e.g., attempt to write data sectors 2, 3 and 5 of FIG. 2C). In the example of FIG. 2C, the control circuitry 20 skips writing data sector 3 during the second revolution (e.g., due to a detected off-track condition) and then writes data sector 3 during a third revolution of the disk.
In order to simplify the complexity of the control circuitry 20, in one embodiment the write data is re-encoded into the full codeword in connection with each retry revolution of the disk even though only part of the full codeword may be written during each retry revolution. FIG. 3A shows example control circuitry 20 according to an embodiment wherein the write data received from the host is stored in a buffer 46. During a first revolution of the disk, the write data for multiple data sectors (five data sectors in the example of FIG. 3A) is transferred from the buffer 46 to an encoder 48 which generates the codeword to be written to the disk 18. In one embodiment, a data sector of the codeword is written to the disk 18 only if a write gate 50 is enabled. This is illustrated in FIG. 3B wherein during a first revolution of the disk data sectors 1 and 4 are written since the write gate is enabled (data sectors 2, 3 and 5 are skipped due to a detected off-track condition). During a second revolution of the disk, the same write data is transferred form the buffer 48 to the encoder 50 in order to regenerate the full codeword, and then the control circuitry 20 attempts to write the previously skipped data sectors by enabling the write gate 50 when the head reaches a previously skipped data sector. Accordingly in this embodiment, the write channel of the control circuitry 20 may operate essentially the same during each retry revolution of the disk except for enabling/disabling the write gate 50 as needed.
Operating the write channel as if the entire codeword were written during each revolution of the disk simplifies the implementation of the write channel. In addition, in one embodiment the write channel operates in real time meaning the encoder 50 is able to encode each codeword on-the-fly during each revolution of the disk. Accordingly, regenerating each codeword during each retry revolution may not decrease the throughput of the disk drive since the write channel operates essentially the same as during the first revolution. Still further, operating the write channel essentially the same during the retry revolutions (by regenerating each codeword) avoids the additional memory that may otherwise be required if each full codeword were buffered by the write channel (rather than regenerated). That is, in one embodiment each codeword may be encoded and written to the disk on-the-fly such that only a small amount of the encoded data for a codeword may be buffered by the write channel as the codeword is written to the disk.
Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
While the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, solid state drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.

## Claims

1. A data storage device comprising:
a disk comprising a plurality of data sectors;
a head actuated over the disk; and
control circuitry configured to:
during a first revolution of the disk, first encode write data into a codeword spanning at least a first data sector and a second data sector and write a first part of the codeword to the first data sector; and
during a second revolution of the disk, second encode the write data into the codeword and write a second part of the codeword to the second data sector.

2. The data storage device as recited in claim 1, wherein during the first revolution of the disk the control circuitry is configured to disable writing the second part of the codeword to the second data sector.

3. The data storage device as recited in claim 2, wherein the control circuitry is further configured to disable the writing due to a detected off-track condition.

4. The data storage device as recited in claim 2, wherein the control circuitry is further configured to disable the writing by disabling a write gate.

5. The data storage device as recited in claim 1, wherein during the first revolution of the disk the control circuitry is further configured to:
first encode the write data into the codeword spanning at least the first data sector, the second data sector, a third data sector and a fourth data sector; and
write a third part of the codeword to the third data sector following the second data sector.

6. The data storage device as recited in claim 5, wherein during a third revolution of the disk the control circuitry is further configured to:
third encode the write data into the codeword; and
write a fourth part of the codeword to the fourth data sector.

7. The data storage device as recited in claim 1, wherein the control circuitry is further configured to:
store the write data in a buffer, including the write data for the first and second data sector;
during the first revolution of the disk, transfer the write data for the first and second data sector from the buffer to an encoder configured to encode the write data into the codeword; and
during the second revolution of the disk, transfer the write data for the first and second data sector from the buffer to the encoder configured to encode the write data into the codeword.

8. A method of operating a data storage device, the method comprising:
during a first revolution of a disk, first encoding write data into a codeword spanning at least a first data sector and a second data sector and writing a first part of the codeword to the first data sector; and
during a second revolution of the disk, second encoding the write data into the codeword and writing a second part of the codeword to the second data sector.

9. The method as recited in claim 8, wherein during the first revolution of the disk further comprising disabling the writing of the second part of the codeword to the second data sector.

10. The method as recited in claim 9, further comprising disabling the writing due to a detected off-track condition.

11. The method as recited in claim 9, further comprising disabling the writing by disabling a write gate.

12. The method as recited in claim 8, wherein during the first revolution of the disk further comprising:
first encoding the write data into the codeword spanning at least the first data sector, the second data sector, a third data sector and a fourth data sector; and
writing a third part of the codeword to the third data sector following the second data sector.

13. The method as recited in claim 12, wherein during a third revolution of the disk further comprising:
third encoding the write data into the codeword; and
writing a fourth part of the codeword to the fourth data sector.

14. The method as recited in claim 8, further comprising:
storing the write data in a buffer, including the write data for the first and second data sector;
during the first revolution of the disk, transferring the write data for the first and second data sector from the buffer to an encoder configured to encode the write data into the codeword; and
during the second revolution of the disk, transferring the write data for the first and second data sector from the buffer to the encoder configured to encode the write data into the codeword.

15. Control circuitry configured to:
during a first revolution of a disk comprising a plurality of data sectors, first encode write data into a codeword spanning at least a first data sector and a second data sector and cause a head for the disk to write a first part of the codeword to the first data sector; and
during a second revolution of the disk, second encode the write data into the codeword and cause a head for the disk to write a second part of the codeword to the second data sector.

16. The control circuitry as recited in claim 15, wherein during the first revolution of the disk the control circuitry is configured to disable writing the second part of the codeword to the second data sector.

17. The control circuitry as recited in claim 16, wherein the control circuitry is further configured to disable the writing due to a detected off-track condition.

18. The control circuitry as recited in claim 16, wherein the control circuitry is further configured to disable the writing by disabling a write gate.

19. The control circuitry as recited in claim 15, wherein during the first revolution of the disk the control circuitry is further configured to:
first encode the write data into the codeword spanning at least the first data sector, the second data sector, a third data sector and a fourth data sector; and
cause the head to write a third part of the codeword to the third data sector following the second data sector.

20. The control circuitry as recited in claim 19, wherein during a third revolution of the disk the control circuitry is further configured to:
third encode the write data into the codeword; and
cause the head to write a fourth part of the codeword to the fourth data sector.

21. The control circuitry as recited in claim 15, wherein the control circuitry is further configured to:
store the write data in a buffer, including the write data for the first and second data sector;
during the first revolution of the disk, transfer the write data for the first and second data sector from the buffer to an encoder configured to encode the write data into the codeword; and
during the second revolution of the disk, transfer the write data for the first and second data sector from the buffer to the encoder configured to encode the write data into the codeword.