Abstract:
A servo controller includes a first device that determines an adjusted servo-to-servo skew value. A servo field timer increments a timer value between consecutive servo fields, receives the adjusted servo-to-servo skew value, and adjusts an incremented timer value between the consecutive servo fields based on the adjusted servo-to-servo skew value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/384,992 filed Mar. 10, 2003. The disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     This is application is related to the following U.S. patent applications, filed on even date herewith and incorporated herein by reference in their entirety: “METHOD AND SYSTEM FOR SUPPORTING MULTIPLE EXTERNAL SERIAL PORT DEVICES USING A SERIAL PORT CONTROLLER IN EMBEDDED DISK CONTROLLERS”, U.S. patent application Ser. No. 10/385,039 (now U.S. Pat. No. 7,039,771), filed Mar. 10, 2003, with Michael Spaur and Ihn Kim as inventors. 
     “METHOD AND SYSTEM FOR EMBEDDED DISK CONTROLLERS”, U.S. patent application Ser. No. 10/385,022 (now U.S. Pat. No. 7,080,188), filed Mar. 10, 2003, with Larry L. Byers, Paul B. Ricci, Joesph G. Kriscunas, Joseba M. Desubijana, Gary R. Robeck Michael R. Spaur and David M. Purdham, as inventors. 
     “METHOD AND SYSTEM FOR USING AN EXTERNAL BUS CONTROLLER IN EMBEDDED DISK CONTROLLERS” U.S. patent application Ser. No. 10/385,056 (now U.S. Pat. No. 7,219,182), filed Mar. 10, 2003, with Gary R. Robeck, Larry L. Byers, Joseba M. Desubijana, and Fredarico E. Dutton as inventors. 
     “METHOD AND SYSTEM FOR USING AN INTERRUPT CONTROLLER IN EMBEDDED DISK CONTROLLERS”, U.S. application Ser. No. 10/384,991 (now U.S. Pat. No. 7,457,903), filed Mar. 10, 2003, with David M. Purdham, Larry L. Byers and Andrew Artz as inventors. 
     “METHOD AND SYSTEM FOR MONITORING EMBEDDED DISK CONTROLLER COMPONENTS”, U.S. patent application Ser. No. 10/385,042 (now U.S. Pat. No. 7,099,963), filed Mar. 10, 2003, with Larry L. Byers, Joseba M. Desubijana, Gary R. Robeck, and William W. Dennin as inventors. 
     “METHOD AND SYSTEM FOR COLLECTING SERVO FIELD DATA FROM PROGRAMMABLE DEVICES IN EMBEDDED DISK CONTROLLERS”, U.S. patent application Ser. No. 10/385,405 (now U.S. Pat. No. 7,064,915), filed Mar. 10, 2003, with Michael R. Spaur and Raymond A. Sandoval as inventors. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to storage systems, and more particularly to disk drive servo controllers. 
     2. Background 
     Conventional computer systems typically include several functional components. These components may include a central processing unit (CPU), main memory, input/output (“I/O”) devices, and disk drives. In conventional systems, the main memory is coupled to the CPU via a system bus or a local memory bus. The main memory is used to provide the CPU access to data and/or program information that is stored in main memory at execution time. Typically, the main memory is composed of random access memory (RAM) circuits. A computer system with the CPU and main memory is often referred to as a host system. 
     The main memory is typically smaller than disk drives and may be volatile. Programming data is often stored on the disk drive and read into main memory as needed. The disk drives are coupled to the host system via a disk controller that handles complex details of interfacing the disk drives to the host system. Communications between the host system and the disk controller is usually provided using one of a variety of standard I/O bus interfaces. 
     Typically, a disk drive includes one or more magnetic disks. Each disk (or platter) typically has a number of concentric rings or tracks (platter) on which data is stored. The tracks themselves may be divided into sectors, which are the smallest accessible data units. A positioning head above the appropriate track accesses a sector. An index pulse typically identifies the first sector of a track. The start of each sector is identified with a sector pulse. Typically, the disk drive waits until a desired sector rotates beneath the head before proceeding with a read or writes operation. Data is accessed serially, one bit at a time and typically, each disk has its own read/write head. 
       FIG. 1A  shows a disk drive system  100  with platters  101 A and  101 B, an actuator  102  and read/write head  103 . Typically, multiple platters/read and write heads are used (see  FIG. 1C , heads  108 - 111 ). Platters  101 A- 101 B have assigned tracks for storing system information, servo data and user data. 
     The disk drive is connected to the disk controller that performs numerous functions, for example, converting digital data to analog head signals, disk formatting, error checking and fixing, logical to physical address mapping and data buffering. To perform the various functions for transferring data, the disk controller includes numerous components. 
     To access data from a disk drive (or to write data), the host system must know where to read (or write data to) the data from the disk drive. A driver typically performs this task. Once the disk drive address is known, the address is translated to cylinder, head and sector based on platter geometry and sent to the disk controller. Logic on the hard disk looks at the number of cylinders requested. Servo controller firmware instructs motor control hardware to move read/write heads  103  to the appropriate track. When the head is in the correct position, it reads the data from the correct track. 
     Typically, read and write head  103  has a write core for writing data in a data region, and a read core for magnetically detecting the data written in the data region of a track and a servo pattern recorded on a servo region. 
     A servo system  104  detects the position of head  103  on platter  101 A according to a phase of a servo pattern detected by the read core of head  103 . Servo system  104  then moves head  103  to the target position. 
     Servo system  104  servo-controls head  103  while receiving feedback for a detected position obtained from a servo pattern so that any positional error between the detected position and the target position is negated. 
     Typically, servo data is stored on the same surface that stores user data to provide the signals for operating servo system  104 .  FIG. 1B  shows how servo data may be located on a disk platter. Region  106  that stores servo data is typically interspersed between user-data regions  105 . Each user-data region  105  has user-data track segments, and each servo-data region  106  has servo-data track segments. The servo data includes track-identification data used during track-seeking operations, and burst data used during track-following operations. 
     Recorded servo information is shifted (or skewed) from one head to the next. This is referred to as “staggered embedded servo fields”.  FIG. 1C  shows an example of staggered servo fields (“SF”) for a two-platter system using four heads ( 108 - 111 ) on tracks  108 A- 111 A, respectively. It is noteworthy that Heads  108 - 111  is similar to head  103  and throughout the specification are used interchangeably. For example, SF DATA  106 , 106 A,  106 C and  106 E are staggered with respect to each other, as head change occurs from  108  over track  108 A to head  111  over track  111 A. 
     Typically, servo information is coded at the time a disk is manufactured. During disk manufacturing, all servo fields have a controlled time based relationship from one platter surface to another surface. However, due to shock, vibration, thermal expansion, contraction, or any other factors, the angular distance as specified in the servo fields varies from one surface to another. Because the angular distance varies, the amount of time that elapses between the servo fields also varies. During head change (for example, from head  108  to  109 ), servo field timer must be adjusted to control proper capture of servo data to control head position when the selected head for reading transitions from one platter surface to another. 
     Conventional techniques, only during disk calibration, require the servo processor to measure skew between each heads, record actual skew in a table and when head  103  change occurs, adjust the servo timer by the appropriate amount. 
     This technique has disadvantages. For example, during calibration, servo processor resources are used for measuring and recording the values. In addition, the amount of time required by the servo processor to record and recall skew during calibration is not constant. Hence, conventional techniques are not desirable to adjust the time base based on recorded/recalled skew servo information. 
     Therefore, what is desired is an efficient and accurate system for time adjusting based on real time and measured, skew values. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a servo controller (SC) system used in an embedded disk controller is provided. The system includes, a servo timing controller, wherein the servo timing controller includes a first register that stores measured servo skew values at a given time; a first set of registers that receive stored skew values and the measured skew values; and logic that adjusts the skew values based on the measured skew values measured by a reference timer. 
     In another aspect of the present invention, a method for adjusting stored servo skew values based on measured skew values is provided. The process includes, measuring actual skew values during a head change in a read operation; comparing the measured skew values with the stored skew values; adjusting the skew value based on the comparison; and adjusting a servo field timer based on the adjusted skew value. 
     In one aspect of the present invention, time adjustment is based on actual measured values, rather than estimates. This is accurate, real-time, and hence desirable in today&#39;s high-end storage systems. 
     In another aspect of the present invention, measured values may be stored and used to update the estimated skew values stored during manufacturing. 
     This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing features and other features of the present invention will now be described. In the drawings, the same components have the same reference numerals. The illustrated embodiment is intended to illustrate, but not to limit the invention. The drawings include the following Figures: 
         FIG. 1A  shows a block diagram of a disk drive; 
         FIG. 1B  shows an example of how servo data is recorded on a disk platter; 
         FIG. 1C  shows an example of embedded staggered servo fields, used according to one aspect of the present invention; 
         FIG. 2  is a block diagram of an embedded disk controller system, according to one aspect of the present invention; 
         FIG. 3  is a block diagram showing the various components of the  FIG. 3  system and a two-platter, four-head disk drive, according to one aspect of the present invention; 
         FIG. 4  is a block diagram of a servo controller, according to one aspect of the present invention; 
         FIG. 5  is a schematic of a servo timing controller, according to one aspect of the present invention; 
         FIG. 6  is a timing diagram using the servo timing controller, according to one aspect of the present invention; 
         FIG. 7  is a flow diagram of a process for adjusting time base based on measured skew values, according to one aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To facilitate an understanding of the preferred embodiment, the general architecture and operation of an embedded disk controller will be described initially. The specific architecture and operation of the preferred embodiment will then be described. 
       FIG. 2  shows a block diagram of an embedded disk controller system  200  according to one aspect of the present invention. System  200  may be an application specific integrated circuit (“ASIC”). 
     System  200  includes a microprocessor (“MP)  201  that performs various functions described below. MP  201  may be a Pentium® Class processor designed and developed by Intel Corporation® or an ARM processor. MP  201  is operationally coupled to various system  200  components via buses  222  and  223 . Bus  222  may be an Advance High performance (AHB) bus as specified by ARM Inc. Bus  223  may an Advance Peripheral Bus (“APB”) as specified by ARM Inc. The specifications for AHB and APB are incorporated herein by reference in their entirety. 
     System  200  is also provided with a random access memory (RAM) or static RAM (SRAM)  202  that stores programs and instructions, which allows MP  201  to execute computer instructions. MP  201  may execute code instructions (also referred to as “firmware”) out of RAM  202 . 
     System  200  is also provided with read only memory (ROM)  203  that stores invariant instructions, including basic input/output instructions. 
       200  is also provided with a digital signal processor (“DSP”)  206  that controls and monitors various servo functions through DSP interface module (“DSPIM”)  208  and servo controller interface  210  operationally coupled to a servo controller (“SC”)  211 . 
       208  interfaces DSP  206  with MP  201  and allows DSP  206  to update a tightly coupled memory module (TCM)  205  (also referred to as “memory module”  205 ) with servo related information. MP  201  can access TCM  205  via DSPIM  208 . 
     Servo controller interface (“SCI”)  210  includes an APB interface  213  that allows SCI  210  to interface with APB bus  223  and allows SC  211  to interface with MP  201  and DSP  206 . 
     SCI  210  also includes DSPAHB interface  214  that allows access to DSPAHB bus  209 . SCI  210  is provided with an analog to digital and a digital to analog converter  212  that converts data from analog to digital domain and vice-versa. Analog data  220  enters module  212  and leaves as analog data  220 A to a servo drive  221 . 
     SC  211  has a read channel device (RDC) serial port  217 , a motor control (“SVC”) serial port  218  for a “combo” motor controller device, a head integrated circuit (HDIC) serial port  219  and a servo data (“SVD”) interface  216  for communicating with various devices. 
       FIG. 3  shows a block diagram with disk  100  coupled to system  200 , according to one aspect of the present invention.  FIG. 3  shows a read channel device  303  that receives signals from a pre-amplifier  302  (also referred to as a Head Integrated Circuit (“HDIC”)) coupled to disk  100 . One example of a read channel device  303  is manufactured by Marvell Semiconductor Inc.®, Part Number 88C7500, while pre-amplifier  302  may be a Texas instrument, Part Number SR1790. Servo data (“SVD”)  305  is sent to SC  211  and processed, as discussed below. 
     A motor controller  307 , (for example, a motor controller manufactured by Texas Instruments®, Part Number SH6764) sends control signals  308  to control actuator movement using motor  307 A. It is noteworthy that spindle  101 C is controlled by a spindle motor (not shown) for rotating platters  101 A and  101 B. SC  211  transmits certain control commands to motor controller  307 . An example is provided, SV_SEN (enables motor controller  307 ), SV_SCLK (clock signal) and SV_SDAT (servo data). 
       FIG. 4  shows a block diagram of SC  211 , according to one aspect of the present invention.  FIG. 4  shows a servo timing controller (“STC”)  401  that automatically adjusts the time base when a head change occurs, according to one aspect of the present invention, as discussed below. 
     Servo controller  211  includes an interrupt controller  411  that can generate an interrupt to DSP  206  and MP  201 . Interrupts may be generated when a servo field is found (or not found) and for other reasons. 
     SC  211  includes a servo monitoring port  412  that monitors various signals to SC  211 . 
     Once STC  401  completes the start sequence, track follow controller  402  may be used to track head position and perform the correction calculations to control head position. 
     SC  211  also uses multi rate timer  403  that allows correction of position multiple times per servo data sample. This allows data to move from DSP  206  to motor controller  307 . 
     SC  211  uses a pulse width modulation unit (“PWM”)  413  for supporting control of motor  307 A PWM, and a spindle motor PWM  409  and a piezo PWM  408 . 
     SC  211  also has a serial port controller  404  for controlling various serial ports  405 - 407 . 
     MP  201  and DSP  206  use read channel device  303  for transferring configuration data and operational commands through SC  211  (via read channel serial port interface  406 ,  FIG. 4 ). 
       FIG. 5  shows a detailed block diagram of STC  401 . STC  401  includes a skew timer register  525  that stores measured skew values when a head change occurs, for example, from head  108  to  109 , as shown in  FIG. 1C . At servo detection, timer control logic  500  captures the value of reference timer  524  in skew value register  525 . Firmware retrieves register  525  contents and transfers the same to register  523  for adjusting skew and the associated time base. In one aspect, register  525  may have six actual measured skew values to accommodate various head movements in a four-head, two-platter system (See  FIG. 1C ). 
     Measured skew values  526  are sent to a set of register  523  and are used for the time base adjustment, in one aspect of the present invention. Registers  523  send measured skew values  514  to multiplexor (“Mux”)  511  when timer control logic  500  sends a sel_skew signal  503  to logic  511 . Signal  503  is sent to Mux  511  that generates the amount of skew  514  and sends that value to logic  512 . In one aspect, logic  512  may be an arithmetic logic unit. 
     Logic  512  also receives signal  502  from SF timer control logic  500 . Signal  502  instructs logic  512  whether to add or subtract the amount of skew from the recorded skew values. Based on signal  502 , logic  512  generates the adjusted skew value  512 A, which is then sent to Mux  509  that also receives a reset value from register  508 . Mux  509  generates the adjusted value  513  and sends it to SF timer  510 . SF timer  510  then generates the adjusted time base value  510 A, which is sent to a decoder  516 . Based on signal  510 A, a skew/time adjustment signal  518  is generated. Signal  510 A provides the current time base for the entire system of  FIG. 5 . 
     It is noteworthy that signal  512 A may be sent directly to SF timer  510  instead of register  508 . 
     SF timer  510  may be adjusted at any particular time by specific amounts. 
     Signal  505  is used to control Mux  509 , while signal  504  is used to control SF timer  510 . 
     Signals  517  (max_cnt) indicates the time to reset reference timer  524 . 
     SF timer  510  is used to control the generation of signal  518  that provides the pointer to one of the skew adjustment values. In addition, Signal  518  indicates the time to use one of the skew values (in register  523 ). 
       FIG. 6  graphically illustrates the foregoing adaptive aspects of the present invention of adjusting skew based on real-time measured values.  FIG. 6  shows two heads  611  and  612  (similar to heads  108 - 111 ) with staggered servo fields  602 ,  607 ,  604  and  609 . Original servo field adjustment values (as set during manufacturing and stored in register set  523 ) are not shown.  FIG. 6  shows the estimated skew adjustment  617  when head change occurs from  611  to  612 . 
     Servo field counter value  614  is stored in a servo field counter register (not shown) located in STC  401 . 
     Reference timer  524  value  615  is not adjusted for skew. Skew measurement  618  is based on actual measured skew value, while data is being read from a platter after a head change occurs. 
       FIG. 7  shows a flow diagram of executable-process steps for adjusting SF timer based on real-time measured skew values. 
     In step S 700 , the process stores the skew values. This is done during manufacturing of the disk drive. 
     In step S 701 , the estimated skew values (either manufacturing values or adjusted previously, at any given time) are recalled from register  523  and used to adjust timer  510 . This adjustment is based on the output of logic  512  and register  523  values. 
     In step S 702 , the actual skew is measured after a head change. Reference timer  524  measures the actual skew. Measured skew values are loaded into registers  523 . This may be performed by system firmware. 
     In step S 703 , the measured skew value is compared to the stored skew values in step S 701 . This task is performed by DSP  206 . 
     In step S 704 , skew values are adjusted based on the comparison. The adjusted value is then sent to register  523  for future use. The process then moves back to step S 701  and the loop continues. Hence, the estimated skew values are adjusted real time based on the measured values. 
     In one aspect of the present invention, SF timer  510  controls skew adjustment based on actual measured values, rather than estimates. This is accurate, real-time, and hence desirable in today&#39;s high-end storage systems. 
     In another aspect of the present invention, measured values may be stored and used to update the estimated skew values stored during manufacturing. 
     Although the present invention has been described with reference to specific embodiments, these embodiments are illustrative only and not limiting. Many other applications and embodiments of the present invention will be apparent in light of this disclosure and the following claims.