Abstract:
An embodiment of the present invention is a head disk assembly (HDA) simulator that outputs a flexible, totally electronic simulation of an HDA. It outputs a programmable standard HDA signal. As such the HDA simulator generates the head signal that a functioning, already servo-written HDA would provide. This signal can be ideal, eliminating any anomalies and inconsistencies inherent in electromechanical devices. Quantifiable amounts of anomalies can be systematically introduced to allow design margin testing. The HDA simulator is controlled in two ways. First, by allowing a user to choose items from four menus. And second, by allowing the user to use a built-in text editor to edit ASCII files that control the servo patterns and simulator operation. Independent channels of repetitive signals are available to specify sync, servo and data patterns. For any given simulated head position, simulated adjacent tracks are generated and then mixed-in at an appropriate ratio. Signals that are unique to each track are also available, to accommodate special requirements such as Grey code.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to signal generators and specifically to instruments capable of simulating the complex signals that a servowritten head disk assembly (HDA) would produce during seek and read operations. 
     2. Description of the Prior Art 
     Traditionally, development of hard disk drive electronics has been delayed until after two critical phases were completed. First, the manufacture of the disk drive electromechanical assembly, and second, the development of a corresponding servowriter. The drive housing with actuator, head and media all had to exist, and the servowriter had to be able to write the respective servo patterns, on the disk(s) before the servo electronics could be tested and debugged. Designers of servo-based floppy, optical and Winchester drives must wait to develop the servo electronics until the actual head disk drive mechanism is built. Later in production, drive electronics are conventionally tested by connecting up a test HDA, or by testing with the target drive mechanics. This method depends on an assumed &#34;normalcy&#34; of the particular HDA, which actually has its own unique characteristics that are not readily controllable. 
     An instrument is needed that will permit test and debug of the drive electronics with the initial servo system design, to avoid the four to six month wait normally required. Such an instrument should also be able to be used in a manufacturing process to test electronic circuit boards safely before mating them with a costly HDA. The simulator should be programmable to simulate various conditions, including worst-case mechanical characteristics, to test the tolerance electronics and its capability to recover. By testing the boards under worst case conditions, the electronics design and production process can be optimized to result in higher product quality, reliability and yields. 
     SUMMARY OF THE PRESENT INVENTION 
     It is therefore an object of the present invention to provide a HDA simulator that can realistically simulate the composite servo signal output of a HDA as though the signal was actually derived from reading the servo pattern from a real disk surface. The creation of such a signal is unique because it simulates the real-world situation where a drive head reads two adjacent tracks simultaneously as if positioning between them. Each track channel is used for position reference. The channels exhibit a variability in the ratio of its constituents when &#34;moving&#34; that indicates head position and travel, thus the servo signal simulates the drive head both while staying on track and in seek mode. The HDA simulator is fully programmable to mimic a targeted, and perhaps not yet fully realized head disk assembly, including the head positioner, mechanical characteristics, and the movement of the read/write head across the media. The designer/user is able to program-in a seek profile, a repeatable runout, a set of media defects, gain, modulation, spindle variations, positioner characteristics and a set of servo patterns. The drive&#39;s servo patterns can be manipulated down to the single transition level. The designer can also simulate closed loop feedback operation. Mechanical phenomena, idiosyncrasies, and anomalies can also be simulated, observed and studied. 
     Briefly, an embodiment of the present invention is a head disk assembly (HDA) simulator that outputs a flexible, totally electronic simulation of a real, or soon to be real HDA. It outputs a programmable standard HDA signal. As such, the HDA simulator mimics the head signal that a functioning, already servo-written HDA would generate. The HDA simulator is controllable in two ways. First, by allowing a user to choose items from four menus; and second, by allowing the user to use a built-in text editor to edit ASCII files that control the servo patterns and simulator operation. Independent channels of repetitive signals are available to specify sync, servo and data patterns. For any given simulated head position, simulated adjacent tracks are chosen, and then mixed-in at an appropriate ratio. Signals that are unique to each track are also available to accommodate special requirements such as Grey code. 
     An advantage of the present invention is that an instrument is provided that can eliminate waiting for the HDA to be designed and fabricated, thus permitting the development and debug of associated boards prior to the .availability of the drive mechanics. The result is faster time-to-market. 
     Another advantage of the present invention is that an instrument is provided that can be used to help develop servo patterns. Servo patterns can be quickly tested and changed. The patterns may be tuned and optimized for best performance of the demodulator without having a working HDA or a working servowriter. This can be an important asset to small firms with limited funds. 
     Another advantage of the present invention is that an instrument is provided that can result in better designs. It may be used to quantifiably generate worst-case signals to test and specify performance of the subsystems of the disk drive. 
     Another advantage of the present invention is that an instrument is provided that can be used in production testing. It can be programmed to generate both ideal and worst-case signals to accurately test servo electronic assemblies through their range of performance specifications. 
     Another advantage of the present invention is that an instrument is provided such that a systems analysis capability can be used to make Bode and Nyquist plots of external devices. 
     These and many other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is block diagram of a head disk assembly (HDA) simulator according to a first embodiment of the present invention; 
     FIG. 2 is a perspective view of the connectors, display, and keyboard used in the simulator of FIG. 1; 
     FIG. 3 is a block diagram of a head disk assembly (HDA) simulator according to a second embodiment of the present invention; 
     FIG. 4 is a block diagram of the position pulse generator used in the simulator of FIG. 3; 
     FIG. 5 is a block diagram of the position simulation filter used in the simulator of FIG. 3; and 
     FIG. 6 is a block diagram of the analyzer used in the simulator of FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention, an HDA simulator 10, mimics an HDA with a head that can seek tracks, and is shown in FIG. 1. HDA simulator 10 comprises a system controller 12, a Bode and Nyquist analysis unit 14, a programmable filter 16, an up/down generator 18, a runout random access memory (RAM) 20, a radial position unit 22, a circumferential position unit 24, an &#34;n&#34; Grey code RAM 26, an &#34;n+1&#34; Grey code RAM 28, an &#34;n&#34; track generator 30, an eight-track definitions RAM 34, an &#34;n+1&#34; track generator 36, a modulation unit 38, a defects unit 40, a track mix unit 42, a pulse shaping filter 44, a head signal output 46, an input 48, a source 50, an analog or digital positioner input 52, an index output 54, an internal clock oscillator 55, an external clock input 56 and a clock switch 57. The radial position unit 22 keeps track of the radial position of the simulated head. The position information is used to select one of eight available tracks for &#34;n&#34; track generator 30 and &#34; n+1&#34; track generator 36. The head position information is also used to generate a mix signal to control the proportions of track &#34;n&#34; to track &#34;n+1&#34; that the simulated head sees. The circumferential position unit 24 keeps track of the circumferential position of the simulated head, and is used to continuously control such items as patterns, modulation, defects and runout, which are all described in more detail below. A fixed frequency internal clock is used to control circumferential position unit 24, but the external clock 56 (e.g., 100 KHz to 48 MHz) may also be used to allow more flexibility, such as is needed to simulate actual spindle velocities. Programmable analog circuits in filter 16 simulate the HDA head positioner&#39;s characteristics for closed-loop operation. VCM inputs can be an analog voltage of 0-5, 0-10, or ±5 volts, with a 20K ohm single-ended input impedance. Eight-bit digital parallel inputs are also preferably accepted on a connector. The pulse shaping filter 44 changes representations of synthesized signals digital pulse into analog signals with shapes typical of magnetic disk recording techniques. The output 46 is a variable differential signal with a 200 millivolt maximum peak-to-peak level. PW50 is nominally 100 nanoseconds and is variable. A pattern generator 60 is formed by the combination of the &#34;n&#34; Grey code RAM 26, the &#34;n+ 1&#34; Grey code RAM 28, the &#34;n&#34; track generator 30, the eight-track definitions RAM 34 and the &#34;n+1&#34; track generator 36. 
     Referring to FIG. 2, system controller 12 is preferably an IBM AT-type compatible personal computer (PC) with a disk operating system, a disk drive 62 that accepts a 1.2 megabyte floppy disk 64 and a twenty megabyte hard disk 65 with a plurality of disk files 66, a user keyboard 68, and a display 70 for the user to view. Disk files 66 may be transferred to and from floppy disk 64 between drives 62 and 65. Display 70 is preferably a EGA-type plasma display, and serial and parallel ports are preferably provided. Spare Industry Standard Architecture (ISA) bus slots are preferably made available for special applications. System controller 12 operates on DOS 3.3, or possibly other more recent versions as they become available, and a disk-resident text editor is provided for editing ASCII files 66 which control many of the operational parameters of HDA simulator 10. A comprehensive user interface is provided. Single level menus are displayed on display 70. Several different functionally organized menus provide complete control of all HDA simulator 10 operations. 
     Menus are selected by pressing one of the function keys of the left side of the keyboard. Such an interface is conventional. After the appropriate menu has been selected, single key menu entry selection provides actuation of the desired function. Servo-pattern type, content (including data field), positioner characteristics, and drive anomalies such as media defects and runout are fully programmable. A disk resident text editor is provided for convenient editing of ASCII files used by the HDA simulator 10. Commonly edited files include PATTERN, TRACK, DISK, and SETUP files. 
     In the form of files, the patterns can be edited by the user and supplemented by the supplier. 
     HDA simulator 10 uses either the internal clock oscillator 55, or the clock input 56 in the circumferential reference for generating servo-patterns. Radial positioning is generated by the system controller 12. HDA simulator 10 has the capability to generate embedded, dedicated or wedge type servo-patterns. The servo-patterns generated consist of frames or sub-frames, which are specified in a PATTERN.TYP file and stored in RAM. The basic servo frames are selected to make up the various servo track types, by a file labeled TRACK.TYP. After the required variations of track types have been established in the TRACK.TYP file (one of files 66), the DISK.TYP file is used to describe the servo pattern surface. System controller 12 examines the contents of the DISK.TYP file and then loads the appropriate TRACK.TYP track data into the eight track RAM 34, according to the theoretical position of the heads. The basic pattern elements (defined by the PATTERN.TYP file are preloaded into the pattern generator 60 (FIG. 1) during start-up and are called by the TRACK.TYP data as the track is being synthesized. The pattern generator provides the special circuitry required for generating the required servo-patterns in proper sequence, and outputs the patterns, synchronous with the positive transitions of the clock signal to the front panel head signal output 46. Since the entire setup pattern is dynamically defined by ASCII character strings, the content of the pattern is virtually limitless. Special encoding can be supported using mathematical expressions to define pattern content such as Grey codes. Track numbering and other disk parameters is determined by data in a SETUP file (one of files 66). 
     The pattern generator develops signals for two servo tracks. These tracks are referred to herein as &#34;n&#34; and &#34;n+1&#34;. The signals from these two tracks are added in the proper ratio, ,as determined by simulated head position relative to the tracks. The mix and amplitude of these signals is influenced by such factors as modulation, runout, and defects, which are all selected from a perturbations menu. 
     Radial head position information is used to select one of eight available tracks for the &#34;n&#34; track generator 30, and one for the &#34;n+1&#34; track generator 36. Head position information is used to generate a signal that controls the mix of track &#34;n&#34; and &#34;n+1&#34; to mimic what an actual head would see in the position simulated. For example, when the head is directly over a track &#34;n&#34; only the signal from track &#34;n&#34; need be used. When the head is halfway between tracks &#34;n&#34; and &#34;n+1&#34;, the mix should probably be equal amounts of &#34;n&#34; and &#34;n+1&#34; track signals. 
     The simulated circumferential position of the head on the disk is used continuously to control the response of HDA simulator 10. Simulation of the patterns, modulation, defects, and runout each require use of circumferential information. A clock is used to pace the circumferential position. An internal clock with several available rates is included. The external (TTL level) clock 56 can be used to allow more flexibility in the setting of the clock frequency, and can be frequency modulated (FM) to simulate instantaneous spindle velocity disturbances. 
     Pulse Filter 
     Filter 44 changes the digital pulse representation of the signal into a simulated analog readback signal. The output is a differential signal with a level of 200 mV p-p (adjustable). The pulse width known to those skilled in the art as &#34;PW50&#34; is normally set at 100 nanoseconds and can be varied as needed. 
     Five ASCII files 66, control HDA simulator 10. The PATTERN.TYP file stores a hex representation of frames used to construct simulated disk tracks. The TRACKNUM.TYP file stores a hex representation of frames that are unique to each track (including those reserved for Grey codes). The TRACK.TYP file specifies up to eight different tracks by building them up from frames that are stored in PATTERN.TYP and TRACKNUM.TYP files. DISK.TYP represents the surface of a disk as built up from tracks stored in TRACK.TYP. The SETUP.TYP file stores basic information about the HDA being simulated and the default values for a plurality of menu selections. 
     Frames are specified in the PATTERN.TYP and TRACKNUM.TYP files. Transitions are represented as hex numbers. Every frame is the same size, from one to sixteen bits. Up to 240 PATTERN.TYP frames are available for use in each track. Up to 2,048 TRACKNUM frames are available, with up to sixteen sectors in each track. The contents of the simulated tracks are contributed to TRACK.TYP file from frames of PATTERN.TYP and TRACKNUM.TYP. Up to eight tracks can be defined with 64,000 frames each. 
     The basic pattern elements, which are preferably stored in RAM, are program selectable and have eight variations. Four of the variations are the conventional sequencing of position and quadrature (P&amp;Q) pulses. The first group has both a sync and a data pulse in addition to the P&amp;Q pulses. It is referred to herein as a one (or mark) frame. The second group has an absent data pulse. It is referred to herein as a zero frame. The presence or absence of a data pulse is detected by a target drive module electronics, supplied by and probably being tested by the user. Unique combinations of zero and one frames allow the encoding of index, track types,. etc. The four basic type one frames are simply numbered one through four. The four basic type zero frames are simply numbered here as five through eight. Table I summarizes the encoding of these eight frames. 
     
                       TABLE I______________________________________Track Type Codes______________________________________Standard Data      11111 =Track Code         55555 66666 77777              or 88888Outer Guard        00011 =Band Track         11155 22266 33377Code               or 44488Track Zero         00110CodeInner Guard        01100 =Band Code          15511 26622 37733              or 48844Index Code         01010 =              15151 26262 37373              or 48484______________________________________ 
    
     Tracks 
     There are typically 5,000 frames per track: one five-frame index code sequence per track, and 4,995 other frames per track. These 4,995 frames are 999 repetitions of unique five-frame code sequences for the respective servo track type. Defining four sets (P&amp;Q variation) of each of the track zone types (outer, zero, data, inner) requires fourteen track types. Referring to Table II, four outer guard band track frame types are tracks 1-4; data track frames are tracks 5-8. Inner guard band track frames are tracks 9-12; and two servo tracks required for track zero are tracks 20-21. The complete set of track definitions are stored in the TRACK.TYP file. 
     
                       TABLE II______________________________________       Index Track Type Code______________________________________Track 1:      15151   999*(11155)Track 2:      26262   999*(22266)Track 3:      37373   999*(33377)Track 4:      48484   999*(44488)Track 5:      15151   999*(55555)Track 6:      26262   999*(66666)Track 7:      37373   999*(77777)Track 8:      48484   999*(88888)Track 9:      15151   999*(15511)Track 10:     26262   999*(26622)Track 11:     37373   999*(37733)Track 12:     48484   999*(45544)Track 20:     37373   999*(33773)Track 21:     48484   999*(44554)______________________________________ 
    
     PROGRAMMING PATTERNS 
     The disk surface is described by three general parameters: disk, track, and pattern. Each of the disk, track and pattern element (frame) parameters are defined in ASCII files 66. The DISK.TYP file is simply a sequential list of which track type is used when. Typically starting from the disk outside diameter to the disk inside diameter. Required pattern elements (patterns of ones and zeros) are read from PATTERN.TYP file and loaded into the pattern generator RAM 34. During HDA operation, system controller 12 uses DISK.TYP file to determine which track data (from TRACK.TYP file) to load into the pattern generator. The track data (from the TRACK.TYP file) is a sequential list of pattern elements, held in a shift register. The clock signal sequences through the track, which in turn calls all the appropriate pattern elements in proper sequence to generate the servo pattern. 
     Disk Parameters 
     The radial layout of the disk is defined (by track types) starting at the outermost track to be written, then working inward toward the spindle. Up to 2048 different track types can be defined. 
     Track Parameters 
     TRACK.TYP file defines the unique combination of available frame types that are used to make up different track types, such as outer guard band, track zero, etc.. Special sequences, such as index coding, are also included. Up to 240 different pattern types can be used to define a track type. Pattern elements can be from one up to sixteen clock cycles. 
     Pattern Element Parameters 
     PATTERN.TYP file contains basic pattern elements. A sequence of pattern elements is used to make up a servo track. These pattern elements are the lowest level of servo-pattern data, consisting of the actual pattern bit ones and zeros. Since most servo-patterns are made up of repeating subsections such as sync, preamble, track fill, etc., these can be defined as pattern elements and can be re-used. Unique track and/or sector numbering requirements are a special case, described below. Each pattern element is assigned a decimal number as an identifier, which is subsequently used in the track definitions contained in a TRACK.NP file (one of files 66). Every pattern element used in TRACK.TYP file must be previously defined in PATTERN.TYP file. 
     Dedicated Surface Servo-Writing 
     Available pattern types are used to make up the different elements which cover the dedicated servo surface(s), according to the design. Exactly the correct number/length of pattern elements are selected for one complete track with no overlap or shortfall. 
     Embedded Servo-Writing 
     Embedded servos require special considerations. Position bursts must be simulated one-half of a data track off from data track center. To accommodate this, every track is simulated twice. There are two special tracks for each embedded data track. For a given data track, the first simulation (one-half data track width) is with all normal on-track data such as sync preamble, track number, etc., followed by one of the position bursts. The second simulation is the same, one-half track further in, but contains the other position burst. 
     Track Numbers 
     Track numbers are handled as a special case and are held in file TRACKNUM.TYP file, which is a sequential list of all track numbers. For actual servo-writing, control of the write gate (WG) is required to prevent erasure of other data (such as marks, syncs, gaps, etc.) while the servo bursts are being inserted at their half track intervals. Control of the write gate is accommodated for in programming to achieve compatibility with the servowriter, but is not required for simulation. 
     DISK.TYP file specifies the usage of the different track types used to map out the entire written disk surface. Up to 240 different track types can be defined, in any order. An integer preceding the track type specifies a number of repetitions. Track types enclosed in brackets will sequentially alternate. 
     Example: DISK.TYP file 30*1 550*(1 2) 40*(3) 
     describes a disk with an outer band of thirty type one tracks, 1100 alternating type one and type two tracks, and forty inner type three tracks. Track types are defined in the following sections. 
     Servo Track Definition 
     The disk surface is made up of user definable tracks. These are used to provide areas such as Guard Bands, track Zero, Data Area, etc. Up to 240 different track types can be used in the TRACK.TYP file. Strings of up to 64K pattern types are listed (in any order) after the track type, identified by a numeric digit. One or more lines of ASCII characters are used for each track type. A hyphen at the end of a line indicates that the description is continued on the following line. 
     Example: TRACKN: 1 232* (4 1) 300 *3 
     Each track &#34;n&#34; will be made up of sections consisting of one &#34;type one&#34; pattern element, one &#34;type two&#34; pattern element, 32 alternating &#34;type four&#34; then &#34;type one&#34; pattern elements, and 300 &#34;type three&#34; pattern elements. Track types must be defined for all unique areas of the disk, such as inner and outer guard bands, data area, etc. These tracks will be used by the DISK.TYP file. 
     Special Considerations 
     Number of pattern elements-Quantity of frames specified in each TRACK.TYP file must be precise. Too few frames result in the remainder of the track containing random frames. Too many pattern elements cause overwriting (overlap) of the beginning elements; 
     Content-System logic requires that the pattern element at the beginning of a track must start with a positive transition, a one. If a negative transition is required at the beginning of a track, a dummy element starting with a one must be inserted. The actual desired first frame is then added at the end of the track as one extra element, which will overwrite the dummy element; and 
     Embedded Servo-Each data track is constructed from two special tracks. Each special track contains one or the other position bursts. 
     PATTERN ELEMENT DEFINITION 
     Tracks are made up of pattern elements. All pattern elements are the same length (defined in the SETUP.TYP file, selectable from one to sixteen bits). This frame content is the lowest level element in the pattern. They define the individual ones and zeros that generate the pulses in the signal. The PATTERN.TYP file contains six columns of hexadecimal characters. Only the first column is used by HDA simulator 10. (The other five columns are used by the servowriter, and are kept in the file for compatibility). Each pattern element is identified by a decimal number. Those numbers are used in TRACK.TYP file to call the pattern elements. 
     Pattern elements may be any combination of ones and zeros, from one to sixteen clock pulses in length. Up to 240 types of pattern elements can be defined. When required, more complex pattern element types can be supported. Because of the inherent flexibility in the pattern elements, track, and disk content can also be defined by mathematical expressions. This supports Grey code embedding and other special considerations. 
     Regardless of their content, pattern elements are identified by a number from zero to 239. They may be combined in any sequence. A sequence of frames can be repeated by enclosing it in parenthesis following the repetition factor and an asterisk. 
     PATTERN.TYP File Format 
     All servo-pattern files 66, including PATTERN.TYP file, must start with a header line. This line is for user convenience only, and is not read by the program. The main program will ignore the first line in the file, thus the header are present as a place holder for the proper file read. 
     Channel 1,2,3 Pattern Data 
     There are three channels in the pattern generator of some commercially available servo-writers. This allows up to three surfaces to be simultaneously written with different data. HDA simulator 10 mimics only use of the first channel (column). The channel (CH1, etc.) columns provide the table of all required pattern elements for all servo tracks. The lines of data in the table can be in any vertical sequence, but the horizontal format of each line are exactly as stated herein. All pattern elements called for in the TRACK.TYP file are listed in this table, or an error will be reported. Unused (extra) pattern elements can be included. 
     The content of each pattern element contains four hexadecimal numbers which together represent sixteen bit positions. Each positive, zero-to-one transition will generate one pulse (not one di-pulse) of the opposite polarity of the previous pulse. 
     The pulse width can be controlled by having adjacent bit positions of the same value, such as. . . 0110 . . . (HEX 6) would provide twice the pulse width of. . . 0010 . . . (HEX 2). The same applies to spacing between pulses. The duration of each pulse is one clock cycle. 
     If, for example, the clock is ten MHz, each pattern element bit position is 100 nanoseconds long. 
     For programming convenience, the pattern element length can be set from one to sixteen bits, although all pattern elements are the same length. The length of the pattern element is defined in the SETUP.TXT file as frame length in clock cycles. For example, (all) pattern elements can be defined to be seven clock cycles long, in which case the least significant nine bit positions will be ignored. Each pulse position requires a positive edge from the clock, therefore there will be one (potential) pulse excursion per two clock cycles. 
     The following information is offered for servowriter compatibility concerns only, and does not necessarily limit the present invention. 
     Write Gate Control 
     There is a write gate control bit for each pattern element bit position. Therefore, a pattern element write gate HEX code of OOOO will turn the write gate on for all bit positions of that element, and FFFF will conversely turn it off for all bit positions. Turning the write gate off can prevent unwanted over writing of previous data. This feature can also be useful for establishing proper track end splice, by turning the write gate off at the required point to prevent overwriting the beginning of the track. 
     Verification Control 
     Like write gate control, above, each bit position can have verification enabled or disabled in the identical manner listed above. Turning verification off for &#34;don&#39;t care&#34; areas, such as fill between sector headers, or guard bands, improves throughput and reduces unnecessary drive rejection. 
     Head Selection 
     Head switching is required when different data are written to different surfaces of the same cylinder simultaneously, or to head switch at the end of a servo track for serial (rather than parallel) writing. When used, it will route the appropriate servo-data to the appropriate head. Each bit position, when set to (binary) one, will cause a head switch to the next sequential head. Random head addressing is not supported. Generally, it is best to define a unique pattern element for head switching only, with the write gate turned off. Head switching can then be done in the data area of the track, then being ready for the next header on the next track. 
     Track and Sector Numbering 
     Track and sector numbering is provided for embedded servos. It is handled as a variation of the pattern element technique, described above. The track and sector numbering mode are enabled by an entry in the SETUP.TXT file. Then the TRACKNUM.TYP file is searched for the first pattern element number in the required sequence which encodes the track or sector code. Subsequent pattern elements required to complete the code are sequentially stored (horizontally) in the TRACKNUM.TYP file. Any coding scheme can be supported, but the required codes are separately listed in the table. Like the DISK, TRACK, and PATTERN.TYP files 66, the TRACKNUM.TYP file is a structured ASCII text file (one of files 66). One may use a word processor (which does not embed control codes other than carriage return or line feed) or write a program to generate the (appropriately formatted) table. HDA simulator 10 can provide a sample program for generating track numbers. 
     TRACKNUM.TYP file pattern element entries can have supporting dummy (zero channel data) entries in the PATTERN.TYP file to provide write gate, verification, and head select control for each pattern element, included for servowriter compatibility. All pattern element positions can contain a number, although actual frame length is set in the SETUP.TXT file. Pattern elements are read from MSB (left) to LSB (right). When less than all sixteen bits (four HEX numbers) of a pattern element are actually used, the LSB can be binary zeroes. All embedded servo tracks are generated twice to accommodate burst offset and provide proper track width. The DISK.TYP and TRACK.TYP files can take this into consideration. Consideration is given to several areas for embedded servos. Each track is generated twice, to accommodate position bursts located one-half track offset from the data track center. The first can contain the track headers information plus one type of position burst. The second can again contain the same track headers information plus the other type of position burst. The next sequential generated track would contain new track header information for the next data track, but the position burst data would remain the same, since it is generating the second pass of that burst for the previous track. All embedded data is generated twice, but position data changes between data track centers, whereas headers change on track centers, and the data (non-header) area of the servo track may be filled with any data, or left unwritten. When the pattern is to be actually used for servowriting, due consideration are given to control of the Write Gate to prevent overwriting adjacent track bursts. Also it is preferable to turn verification off for data frames. Separate control of write gate and verification is provided for each pattern element used. These control fields may be available in the HDA for compatibility with commercially available servo-writers, but are not used during simulation. 
     HDA simulator 10 is operated by a user from computer 60 displaying readily accessible menus, which are functionally organized, and are selected using the function keys. Keyboard 68 is a conventional keyboard that includes these function keys. A key directory menu is available to the user, and is accessed by function key F9. The function keys are summarized in Table III. 
     
                       TABLE III______________________________________F1      Fundamental  Allows a wide range of   Positioning  control of the simulated head                position to read the servo                pattern. Position can be                selected by track number, or                repositioned from its current                location by a specified                increment. Also provides                access to seek operations and                characteristics.F2      Perturbations                Allows input of multiple                drive anomalies such as                modulation (overall media                variation), defects                (scratches across all                tracks), and spindle runout.                A master gain control is also                preferably included.F3      Closed Loop  Provides access to Bode and   Positioning  Nyquist plotting functions,                which can be used internally                or externally. Resonances can                be specified for simulations.                A three pole programmable                filter (see FIG. 5) is also                preferably included to                emulate HDA positioner                performance. Plots of head                trajectory are also provided                in this menu.F4      Low Level    Gives access and control to   Control      utilities and special                functions: editing                configuration files 66,                diagnostics, re-loading files                66 and HDA simulator 10 re-                initialization, low level                port and memory access                commandsF5-     not assignedF9F9      Key Directory                Provide a convenient listing                of menu and Special function                selection keys.F10     Exit to DOS______________________________________ Note: low level port and memory access commands are displayed only in debug mode. 
    
     Clock Source 
     The default clock source is the internal clock. There will be a prompt at the lower left corner of display 70 indicating the clock frequency. To use an external clock source, a TTL clock source is connected to the clock input 56. A clock source entry in the SETUP.TXT file is edited via the F4 menu to enable the external input. Different internal clock frequencies may be obtained by changing the clock divider value in the SETUP.TXT file. The internal crystal may be exchanged for a different (albeit fixed) frequency. 
     Computer Reset 
     By simultaneously pressing the CTRL, ALT, and DEL keys on keyboard 68 momentarily, and then releasing them, computer 60 will reset and the main control program will be re-loaded. 
     Re-Initialize Simulator 
     From keyboard 68, pressing function key F4, and then selecting Re-initialize Simulator, will cause all HDA simulator 10 circuitry to be reset and files 66 to be reloaded. 
     Exiting to DOS 
     From any menu, by pressing F10, then answering Y (yes), the user can then rerun the HDA simulator program by entering MAIN at the DOS prompt. To temporarily exit the HDA simulator 10 main program, but still leave it in memory (to save re-load time), ALT-Z is typed to shell to DOS. EXIT is typed in to return to the main program. 
     Clearing Error Conditions 
     When HDA simulator 10 encounters an abnormal condition, an error is reported on display 70. Subsequent operation is halted until the error is cleared by pressing the escape (ESC) key on keyboard 68. In instances where further operation is impossible or hazardous, the error condition will continue to be displayed and operation halted until the condition causing the error is corrected. 
     User Interface 
     The user interface is menu driven. Most entries only require a single key input of the menu selection. Pressing [RETURN] or [ENTER] is not required for these menu selections. When additional information is needed by the HDA simulator to execute the user&#39;s command, a prompt will appear at the bottom of display 70. In many instances, a default value is presented. It may be accepted by pressing [ENTER], or cleared by the backspace key. When cleared, the new value is entered and [ENTER] is pressed. Menu displays F1 through F4 access track number and microstep position of the head, at the top of display 70. 
     Fundamental Positioning-F1 
     Tracks can be selected by special or user track number. For embedded servos, all user tracks consist of two special (half) tracks, in order to accommodate half track offsets for positioning bursts, while keeping other header information on user (data) track centers. This can also be considered when programming embedded servo patterns. Default micro-steps are sized to be 1/512 the distance between adjacent simulation tracks. Larger values can also be selected (e.g., 256=one-half, etc.). In all cases, head position implies generating the signal that would exist if the drive head were moved to that physical position. Table IV summarizes the above. 
     
                       TABLE IV______________________________________A     Step In -     Each press of this key will Special       change the head position by Track(s)      the number of tracks               specified. Number can be               specified with the L command,               below. Signal will represent               head positioned directly over               a servo track.B     Step In .sub.--               Each press of this key will User track(s) change the head position by               the number of tracks               specified. Number can be               specified with the L command,               below. Signal will represent               head positioned directly over               a data track center.C     Change Micro- Pressing the C key causes the Step          HDA simulator to request a               new value, in micro-steps, to               move when the + or - key is               pressed in this menu. The               default value is specified in               the SETUP file (one of files               66), and is typically 1/512               special track space value.               Range one to 512.D     Seek to First Head will be positioned at Special Track the first HDA simulator 10 ×               track; as specified in the               DISK.TYP file (one of files               66).E     Seek to       When selected, HDA simulator Special Track 10 will ask for a track &#34;n&#34;           number for &#34;n&#34;, and then move               the head to that position.F     Seek to Last  Head will be positioned at Special track the last servo track, as               specified in the DISK.TYP               file (one of files 66).G     Bounce Between               Moves the head continuously Tracks        between two user track               numbers, which are prompted               for. Press the ESC key to               abort the operation.               Movements are controlled by               velocity and acceleration               values.H     Set Velocity  Specifies the rate of change               for head movement in tracks               per milliseconds. Range zero               to 10.sup.38.J     Step Out -    Each press of this key will Special       change the head position by Track(s)      the number of tracks               specified. Number can be               specified with the L command,               below.K     Step Out n#   Each press of this key will User Track(s) change the head position by               the number of tracks               specified. Number can be               specified with the L command,               below.L     Change Step   Changes the number of tracks               moved when the A, B, J, or K               command is issued, in integer               values. Specified in special               tracks. When embedded servo               is used, user track step               increment will be two times               this value.M     Seek to First Head will be positioned at User Track    the first user data track; as               specified in the DISK.TYP               file (one of files 66).N     Seek to User  When selected, the HDA Track         simulator will ask for a               track number for &#34;n&#34;, and               then move the head to that               data track position.O     Seek to Last  Head will be positioned at User Track    the last user track, as               specified in the DISK.TYP               file.P     Execute Seek  Causes seeks to special track File          numbers contained in the               SEEK.TXT file (one of files               66). The SEEK.TXT file may be               altered using the Editor               available in the F4 menu.               Select O (Other) for file to               edit, then enter SEEK.TXT for               the file name.Q     Set           Specifies the Acceleration  acceleration/deceleration               rate to be used during head               moves, in tracks per               milliseconds squared. Range               zero to ten.+     Move In       Pressing the + key causes the               head signal to change as if               the pattern head moved in               toward the spindle by a               specified amount, in micro-               steps. The amount is               specified by the &#34;C&#34; menu               selection, listed above.-     Move Out      Pressing the key causes the               head signal to change as If               the pattern head moved out               from the swindle by a               specified amount, in micro-               steps. The amount is               specified by the &#34;C&#34; menu               selection, listed above.______________________________________ 
    
     Perturbation Menu-F2 
     Three general types of perturbations are possible: modulation, media defects, and spindle runout. All three types amplitude modulate the synthesized head signal: 
     MODULATION causes a sinusoidal modulation typical of media coating variations; 
     DEFECTS cause a once-per-revolution drop in amplitude, programmable in width, position and amplitude. Only scratches across all tracks are selectable, although a special track type could be used to drop out specific pulses on specific tracks; and 
     SPINDLE RUNOUT differentially modulates only the position pulses, to emulate tracks moving side-to-side under the head. 
     Reload commands are used to cause specified perturbations to take affect. Settings are canceled (zeroed) by selecting the menu item, entering zero for the amplitude and then pressing [RETURN]. 
     
                       TABLE V______________________________________A       Modulation One                 Selects a sinusoidal                 amplitude modulation                 which can be specified in                 percent of total                 amplitude and how many                 (integer) cycles per                 revolution. R - Reload                 Gain and Mods causes                 modulations to be                 implemented. Select the                 modulation, enter zero                 for the amplitude and                 press [RETURN] to cancel,                 then reload.B-E     Modulation (&#34;n&#34;)                 See A., above. These                 values are summed with                 all other perturbations.F       Runout One    Selects a differential                 sinusoidal amplitude                 modulation which is                 applied to position                 pulses only. specified in                 percent of total                 amplitude and how many                 cycles per revolution. R -                 Reload Runout to cause                 perturbations to be                 implemented. Select the                 runout, enter zero for                 the amplitude and press                 [RETURN] to cancel, then                 reload.G-I     Modulation (&#34;n&#34;)                 See A, above. These                 values are summed with                 all other perturbations.L       Defect One    Selects an amplitude                 modulation which can be                 specified in percent of                 total amplitude, location                 in respect to Index and                 length in frames (pattern                 elements). Use the S -                 Reload defects to cause                 modulations to be                 implemented. Select the                 modulation, enter zero                 for the amplitude and                 press [RETURN] to cancel                 then reload.M-P     Defect (&#34;n&#34;)  See L, above. These                 values are summed with                 all other perturbations.Q       Gain          Selects overall gain.                 Default value is 100%.                 Specified in percent of                 full output. R - Reload                 gain and mods to cause                 gain setting to be                 implemented. Select gain,                 enter 100 for the                 amplitude and press                 [RETURN] to return to                 full output, then reload.R       Reload Gain,  Causes system controller   Mods and Defects                 12 to read new gain,                 modulation and media                 Defect values and apply                 their summed values to                 the head output signal.S       Reload Runout Causes system controller                 12 to read new runout                 values and apply their                 summed values to the head                 output signal.______________________________________ 
    
     Closed Loop Positioning-F3 
     This menu is used for four general applications: 
     to provide a stand-alone analyzer which will generate Bode plots and Nyquist diagrams of external equipment, such as a real HDA; 
     to plot Bode an Nyquist diagrams showing the response of the internal filter which simulates an HDA, either actual or under design; 
     to provide a closed loop, setting the programmable filter to HDA response characteristics; and 
     to plot the simulated trajectory of the head in closed loop mode. 
     Filter Plot Mode 
     Filter parameters are set to emulate the positioner performance for the target HDA. Where possible, the plotted results are compared with a plot from a similar HDA to verify filter settings. 
     External Loop Mode 
     Filter parameters are set to emulate the target HDA. Where possible, the plotted results are compared with a plot from a similar HDA to verify filter settings. The differential head signal is fed from HDA simulator 10 by a TWINAX BNC connector to the (external) drive electronics. The drive electronics positioner signal is fed into HDA simulator 10. Either an (eight-bit) TTL digital signal is input, or an analog differential signal is input. 
     Analyzer Mode 
     Bode and Nyquist plotting functions can be used on external circuitry. None of the filtering, positioning or perturbation settings affect the analysis operation. See items I-L, below, for controls and operations. Output amplitude is preferably automatically scaled to generate the required input signal. 
     A-Resonance One 
     One of two available resonant points is set in the HDA simulation filter and is specified by frequency and amplitude. (The hardware is discussed in more detail below in connection with FIG. 5.) 
     
                       TABLE VI______________________________________Term            Units   Range______________________________________Frequency       Hz      5Hz-3KHzAmplitude       None    0-100______________________________________ 
    
     Values are cleared by selecting the menu item, entering zero for amplitude, then [RETURN]. 
     B-Resonance Two 
     See item A, above 
     C-Pole One 
     One of three available poles is determined for the HDA simulation filter. (Pole zero is fixed, at zero Hz). It is specified by frequency. The input range is typically five Hz to three KHz. Values are cleared by selecting the menu item, entering zero for the amplitude, then pressing [RETURN]. (The hardware is discussed below in connection with FIG. 5.) 
     D-Pole Two 
     See item C, above. (The hardware is discussed below in connection with FIG. 5.) 
     E-Zero 
     Determines a zero point for the HDA simulation filter. It is specified by frequency. The input range 0-5K Hz. Values are cleared by selecting the menu item, entering zero, then pressing [RETURN]. (The hardware is discussed below in connection with FIG. 5.) 
     F-Filter Gain 
     Sets gain of HDA simulation filter. Range zero to 100. (The hardware is discussed below in connection with FIG. 5.) 
     I-Signal Source 
     Toggles the input signal source (internal to HDA simulator 10, or external) for plotting functions. Internal is default. (The hardware is discussed below in connection with FIG. 5.) 
     J-Frequency Range 
     Selects the range of frequencies used as stimuli when generating plots. Range one Hz to 3000 Hz. Select a lower and upper value. Analyzer automatically steps through a range of points within that range. Eliminating frequencies below ten Hz significantly speeds plot time. 
     K-Generate Bode Plot 
     Causes the analyzer to generate two automatically scaled plots, one amplitude vs. frequency, the other (lagging) phase vs. frequency. Data from this plot is also saved in a file BODE.OUT. 
     L-Nyquist Diagram Half-Size 
     Sets vertical and horizontal scale factors for Nyquist diagrams. This value may be re-selected followed by the generate Nyquist command below, to re-plot the same data at the new scale. Range 0.1 to 10K. 
     M-Generate Nyquist Diagram 
     Causes analyzer to generate an automatically scaled Nyquist diagram. This function may take minutes depending on number of points selected. See also I and J, above, &#34;n&#34; below Data from this plot is also saved in a file (one of files 66): Nyquist.OUT. 
     N-Number of Plot Points 
     Specifies number of samplers to be taken in the frequency range specified above. Interpolation occurs between points. Time to generate a plot increases as number of points increase. Range three to 200 (integer). 
     T-Capture Trajectory 
     When an external position input is fed to front panel J1, this command captures several revolutions of head movement information, relative to time. Vertical (movement) is auto-scaled in tracks. 
     U-Plot Trajectory 
     See T, above. This command causes the head trajectory information captured to be plotted. While the plot is displayed, press F1 to display a list of output options. Data from this plot is also saved in a file (one of files 66): TRAJ.OUT 
     LOW LEVEL CONTROL-F4 
     A-Read Memory Block 
     This menu item is only displayed when debug mode (ALT+D) is active. This function allows inspection of special memory segments used by HDA simulator 10 for various functions. When selected, HDA simulator 10 will request a memory segment (type): 
     P Pattern Memory; 
     F Frame Memory; 
     S Sync Delay (di-pulse Width); 
     I Position Delay (di-pulse Width); 
     R RAM (When optional Frame RAM is installed); and 
     O Other. 
     After the memory has been selected, HDA simulator 10 presents the segment location and the default starting address. This address can be accepted by pressing [ENTER]; or edited by backspacing and entering the desired address, followed by [ENTER]. Next, HDA simulator 10 will specify the ending address, which can be accepted or modified as above. After [ENTER] is pressed, a hex display 70 dump will begin, one display 70 at a time. The dump can be paged down with the space bar and terminated with the escape (ESC) key. 
     D-Reload DISK.TYP File 
     The DISK.TYP file will be reloaded from disk into memory and any edits to it will now affect operation of the HDA. 
     E-Edit File 
     This command will allow the user to edit ASCII files 66 with a text editor. ASCII File types available for editing are: 
     S Setup-General programmable operational parameters; 
     P Pattern-Definition of servo pattern types; 
     T Track-Definition of servo track types; 
     N Track Numbers-Table of track numbers (typically Grey codes) 
     D Disk-Definition of the servo disk(s); and 
     O Other-HDA simulator 10 will request a filename. 
     F-Fill Memory 
     This menu item is only displayed when debug mode (ALT+D) is active. This command will allow the user to fill a contiguous range of memory locations with one hex value. This function allows alteration of special memory segments used by the HDA simulator for various functions. When selected, the HDA simulator will request a memory segment (type): 
     P-pattern memory 
     F-frame memory 
     S-Sync delay (di-pulse width) -position delay (di-pulse width) 
     R-RAM (When optional frame RAM is installed) 
     O-Other. 
     After the memory has been selected, HDA simulator 10 presents the segment location and the default address. This address can be accepted by pressing [ENTER]; or edited by backspacing and entering the desired address, followed by [ENTER]. Changing this type of memory location affects subsequent HDA simulator 10 operation immediately, but is not saved to disk. 
     I-Input Port 
     This menu item is only displayed when debug mode (ALT+D) is active. This function allows the user to read registers. HDA simulator 10 will request the port address and after [ENTER] is pressed, will return the hex contents of that location. 
     O-Output Port 
     This menu item is only displayed when debug mode (ALT+D) is active. This function allows the user to write registers. The HDA simulator will request the port address and after [ENTER] is pressed, will change the hex contents of that location. 
     P-Reload PATTERN.TYP file 
     The PATTERN.TYP file will be reloaded from HDA simulator disk into memory and any edits to it will now affect operation of the HDA. 
     R-Read Memory 
     This menu item is only displayed when debug mode (ALT+D) is active. This command allows the user to read a single memory location. This function allows inspection of special memory segments used by the HDA simulator for various functions. When selected, the HDA simulator will request a memory segment (type): 
     P-pattern memory 
     F-Frame Memory 
     S-sync delay (di-pulse width) -position delay (di-pulse width) 
     R-RAM (When optional frame RAM is installed) 
     O-Other 
     After the memory has been selected, HDA simulator 10 presents the segment location and the default address. This address can be accepted by pressing [ENTER]; or edited by backspacing and entering the desired address, followed by [ENTER]. 
     S-Reload the SETUP.TXT File 
     The SETUP.TXT file will be reloaded from HDA simulator 10 disk into memory and any edits to it will now affect operation of the HDA. 
     T-Reload TRACK.TYP File 
     The TRACK.TYP file will be reloaded from HDA simulator 10 disk into memory and any edits to it will now affect operation of the HDA. 
     W-Write Memory 
     This menu item is only displayed when debug mode (ALT+D) is active. This command allows the user to write a single memory location. This function allows alteration of special memory segments used by HDA simulator 10 for various functions. When selected, HDA simulator 10 will request a memory segment (type): 
     P-pattern memory 
     F-frame memory 
     S-sync delay (di-pulse width) -position delay (di-pulse width) 
     R-RAM (When optional frame RAM is installed) 
     O-other 
     After the memory has been selected, HDA simulator 10 presents the segment location and the default address. This address can be accepted by pressing [ENTER], or by edited by backspacing and entering the desired address, followed by [ENTER]. Changing this type of memory location affects subsequent HDA simulator 10 operation immediately, but is not saved to disk. 
     X-Run Diagnostics 
     This command causes diagnostics to be run. If an error condition is detected, an error code is shown on display 70. The error code will remain until the escape (ESC) key is pressed. The diagnostic will halt at the error and will not proceed until the first error is cleared, since that error may cause other apparent errors which are a result of the first error. Press [ESC] to abort the diagnostic. F5 is pressed to clear the message from the display 70. 
     Z-SAVE SETUP Parameters 
     Execution of this command will cause variables used in the other menus to be saved and used as default values for later use. 
     Special Function Keys 
     Special functions can preferably be accessed from any menu by holding down the ALT key and pressing the appropriate alphabetical key. When the selected function is enabled, an indicator will appear at the lower right corner of display 70 in reverse video. These are summarized in the following table. In the table, &#34;toggle&#34; means that each time the key is depressed, the controlled function will change state from enabled to disabled, or disabled to enabled. 
     
                       TABLE VII______________________________________ALT C   Set-Reset   Activating this function   Continuous  causes certain functions to   Flag        repeat on a continuing basis,               within certain timing and               logic condition intervals.               Pressing the escape (ESC) key               will terminate the particular               continuing function. This is               a toggle activate/deactivate               function. When set ON,               selecting it again will turn               the function OFF. A C status               message is presented at the               bottom line of the current               menu when this function is               active.ALT D   Set-Reset   Activating this function   Debug Flag  causes additional information               to be presented on-display 70               when certain functions are               active. It can be useful in               setup and problem solving.               When operating in debug mode,               some operations may halt               after display of results.               Pressing [ESC] continues               operations. This is a toggle               activate/deactivate function.               When set ON, selecting it               again will turn the function               OFF. A D status message is               presented at the bottom line               of the current menu when this               function is active.ALT L   Select      This function selects either   Positioner  the analog (default) or   Input       digital positioner input at               J1 on the front panel.               Pressing these keys also               causes the current mode to be               displayed.ALT R   Activate-   This mode provides user   Terminate   programming for a sequence of   Record      operations. A special test   Sequence    sequence can be recorded and               then executed once or               repetitively until               interrupted. When this mode               is activated, every               subsequent keyboard 68 entry               is stored, including menu               function (F1, etc.) keys.               Variables such as track               numbers, etc. (prompted for               at the lower center of the               display 70) can not be               included in the recorded               sequence. When the desired               sequence has been entered,               press ALT R a second time to               terminate recording. At this               time the user will be               prompted for a (DOS) file               name into which the user&#39;s               key sequence will be stored.ALT S   Start-Stop  This command allows execution   Sequence    of a recorded sequence of key               presses which were stored               using the ALT R command,               above. HDA simulator 10 will               prompt the user for the (DOS)               filename containing the               stored sequence. The user can               know the filename prior to               activating this function. If               needed, use the F10 key to               exit to DOS, then use the DOS               Dir command to retrieve the               filename. If the user used               the &#34;.SEQ&#34; extension,               entering *.SEQ will display               the list of the user&#39;s               sequence files 66. After the               file has been retrieved it               will continue to execute               until ALT S is again input.               If commands were stored which               require a variable to be               entered (such as track               Number, the programmed               sequence will halt until the               variable is keyed in,               followed by pressing [ENTER].               Then the sequence will               resume. See ALT R for               additional information.ALT T   Set-Reset   This function disables   Test Flag   protective features to allow               fuller control of functions,               particularly for HDA               simulator 10 testing and               troubleshooting. This is a               toggle activate/deactivate               function. When set ON,               selecting it again will turn               the function OFF. A &#39;T status               message is presented at the               bottom line of the current               menu when this function is               active. Reboot after using               this feature.ALT X   Exit to     Terminates HDA simulator 10   DOS         program and exits to MS-DOS.ALT Z   Shell Exit  Terminates HDA simulator 10   to DOS      program, but leaves it in               memory. Exits via DOS Shell               to MS-DOS. To return to HDA               simulator 10 program, type               EXIT [RETURN].______________________________________ 
    
     PROGRAMMING OPERATIONAL PARAMETERS 
     These parameters are used to establish application-unique factors which can be modified to meet specific requirements. The text editor can be used to edit one of files 66, including the servo-pattern description files DISK.TYP file, TRACK.TYP file and PATTERN.TYP file, described herein. 
     Parameter File 
     An ASCII file called SETUP.TYP file is used to hold these parameters. It is easily edited using the text editor provided in the low level control menu accessed by the F4 function key. Parameters controlled by this file include: 
     track numbering; 
     clock data; 
     head trajectory data; 
     default perturbation values; and 
     default closed loop operations values. 
     A feature in the F4 menu, SAVE SETUP, saves variables entered in other menus to the SETUP.TXT file as default values. 
     A text editor is provided with HDA simulator 10 on hard disk 65. The editor is accessed under the low level control engineering mode menu F4. 
     OPERATIONAL PARAMETERS 
     These operational parameters are listed in Table VIII in the sequence they are positioned in the SETUP.TXT file. Some items may not be listed in the user&#39;s SETUP file if they are not applicable to the user&#39;s configuration. 
     
                       TABLE VIII______________________________________Initial   Sets the default value in n, where oneMicrostep microstep is defined as one 512.sup.th of aIncrement full special track change. Integer.     Example: entering 256 would make each     microstep one-half(256/512) of a special     track. Range 1-512 (integer).Initial   Sets the default nurber of specialHDA       tracks moved when a Step IN/OUT nSimulator special tracks command is issued. Range10 Step   1-20,000 (integer).IncrementNumber of Sets ratio of special tracks to clientSpecial   tracks. Normally set to 1 for dedicatedTracks    surface; 2 for embedded, to support halfPer       track offsets for position bursts. RangeClient    1-8 (integer).TrackNumber of Provides an offset for specialSpecial   applications. Range 0-1K (integer).TracksBeforeFirst(User)DataTrackHDA       Sets starting special track number.Simulator Range -99 to +99.10 FirstTrackNumberClient    Sets track numbering display method forFirst     Client Tracks. Range -99 to +99. DoesTrack     not affect Grey code values.NumberClocks    Each pattern element location in memoryper Frame is sixteen bits. For some patterns it is     more convenient to use less than all 16     locations. This parameter defines how     many of the sixteen bits are used,     starting at the left-most (MSB) bit.     Range 1-16.Clock     Informs the HDA simulator 10 program ofFrequency the frequency of the Internal Clock     crystal. This Crystal can be changed to     a different value than that originally     installed, to obtain special clock     frequencies. See Clock Divider, below.     Theoretical range 1-80 MHz.Clock     Specifies a divider value for theDivider   internal clock frequency (above). Range     two through 255, integer. Does not     affect external clock input.Track     When set to T (True), instructs theNumbers   program to use the contents of theRequired  TRACKNUM.TYP file for track numbering.     Typically for embedded servos.Head      Sets the open loop seek rate, in specialMovement  tracks per millisecond. Range 1-1038.VelocityHead      Sets the open loop acceleration andMovement  deceleration rates emulated during seeksAccel.    in Tracks per milliseconds squared.     Range 1-10.sup.38.Number of Sets maximum number allowed, up to five.Mod.Perturb.Number of Sets default values for up to fiveModulation     selections.Cyclesper Rev.Modulation     Sets default amplitude values in percentAmount    of total amplitude. Up to five     selections. Range 0-100%.Gain      Sets default value for overall gainAmount    setting, in percent of maximum. Range 0-     100%.Number of Sets default number of defects, maximumDefects   five.Defect    Sets default values for defect locationsFrame     referenced to index, in frames (patternLocation  elements). Range 1K-64K (integer).Defect    Sets default values for lengths ofSpan      defects, in frames (pattern elements).     Range 1K-64K (integer).Defect    Sets default values for up to fiveAmplitude defects amplitudes, in percent of     maximum. Range 0-100%.Runout    Sets the allowable number of runouts, upFreqs.    to five.Runout    Sets default values for up to fiveCycles    runouts, in cycles per revolutionper Rev.Runout    Sets default values for up to fiveAmount    runout amplitudes in percent of maximum.     Range 0-100%.Digital   Sets the default source for the filter.Filter    T = Digital input, 8 bit. F = AnalogInput     input, -5 to +5 volts.SourceFirst,    Sets whether resonances will beSecond    displayed as menu items T YES, F = NOResonanceEnabledFirst,    Sets whether filter pole menu items willSecond    be displayed. T = YES, F = NOPoleEnabledZero      Sets whether the zero filter functionEnabled   menu selection will be displayed. T =     YES, F = NOFirst,    Sets default values for resonanceSecond    amplitudes. Range zero to 100.ResonanceAmplitudeFirst,    Sets default values for resonanceSecond    frequencies. Range 5Hz to 3K Hz.ResonanceFrequencyFirst     Sets default values for pole frequency.Pole      Range 1 Hz to 256 Hz.FrequencySecond    Sets default values for pole frequency.Pole      Range 5Hz to 3K Hz.FrequencyZero      Sets the default value for the filterFrequency Zero frequency. Range 5 Hz to 3K Hz.Filter    Sets the default gain value for theGain      filter. Range zero to 100.Closed    Sets the default value for closed loopLoop      runout, in cycles per revolution rangeRunout    1K-32K (integer).CyclesPer Rev.Closed    Sets the default value for closed loopLoop      amplitude. Range zero to 100. Units notRunout    defined.Amplitude______________________________________ 
    
     FIG. 3 illustrates a second embodiment of the present invention which is an HDA simulator 80 comprising a positioner simulation filter 82, a position pulse generator 84, a radial position counter 86, an analyzer measurement input 88, an analyzer stimulus generator 90, a microcomputer (PC/AT CPU) 92, a pattern element RAM 94, an eight track RAM 96, an open loop input 98, an interconnect bus 99, a digital-to-analog converter (DAC) 100, an internal crystal (XTAL) clock 102, an internal variable clock 104, a clock select and divider 106, a circumferential position counter 108, a track &#34;n&#34; generator 1107 a track &#34;n+1&#34; generator 112, a position proportioning and summing stage 114, a signal shaper 116, a write data acquisition unit 118, a spindle motor simulator 120, a drive board interface controller 122, a modulation-defect-gain RAM 124, a DAC 126, a noise generator 128, a multi-board I/O multiplexer 130, a head output signal 132, a drive position input signal 134, a digital input signal 136, a data input 138, a write gate input 140 and an external clock input signal 142. HDA simulator 80 is similar in function and purpose to HDA simulator 10 and the above described menus, files 66, patterns and programming are also applicable to HDA simulator 80, so their description will not be repeated here. 
     In FIG. 4, position pulse generator 84 comprises a reference frequency source 150, a position pulse voltage controlled oscillator (VCO) 152, a rate comparator 154 that produces up and down pulse outputs, a feedback DAC 156, and a feedback counter 158 to net the up and down pulse outputs. CPU 92 controls radial position counter 86 over bus 99 for the signal to the position proportional summing stage 114 based on the action of position pulse generator 84. 
     To simulate disk read/write, HDA simulator 80 generates a clock to synchronize circumferential movement and uses position counter 86 to track radial (in/out) head movement. HDA simulator 80 will operate either closed loop with drive board 122 receiving an input or open loop with a synthesized radial position. 
     For an open loop operation mode, radial position counter 86 is controlled directly by PC/AT CPU 92 (which is equivalent to system controller 12 in the first embodiment). Micro-track positions are loaded in accordance with an open loop positioning menu. The output of radial position counter 86 is used to determine the appropriate track types to load from eight-track RAM 96 into track generators 110 and 112 and the proportions of &#34;n&#34; and &#34;n+1&#34; to be summed for a simulation of the head position (e.g., on/off track). Circumferential tracking is derived through clock selector and divider 106 from one of three possible clocks: external clock 142, internal high precision clock 102 or internal variable clock 104. Varying the clock rate allows simulation of an HDA spin-up/spin-down and spindle speed variations. The selected clock is divided according to the desired rate and the length of each pattern element used to build up the tracks. The chosen signal clocks the track data (that has been pre-loaded into the track generator 110 and 112) to the position-proportional summing stage 114. Quantified track-to-track phase incoherence can be mimicked. This is done by delaying the output of one track, &#34;n&#34; or &#34;n+1&#34;, with respect to the other. The position-proportional summing stage 114 selects the amplitudes for the track &#34;n&#34; and track &#34;n+1&#34; data to be proportionally related to the radial position counter/runout input from DAC 100. Signals &#34;n&#34; and &#34;n+1&#34; are then summed. The amplitudes are also influenced by perturbation generator signal input from DAC 126. The perturbation generation supports modulation, media defect and overall gain artifact selections from a perturbation menu accessible by the user. PC/AT CPU 92 (under program control, of course) loads a shift register similar to the track generators 110 and 112 with a summation of the three types of perturbations. The shift register is clocked by the track data and so the summation will be in sync with the track data. The output arrives at the position-proportional summing stage 114 to affect the summed amplitude as had been directed by the user. Using selectable resistor-inductor-capacitor (RLC) values or a programmable filter unit, shaper 116 contours pulses in such a way that they appear to be typical of conventional magnetic disk readback circuits. The pulse width (PW50) value is controlled by PC/AT CPU 92. The signal amplitude of head output 132 is typically 100 millivolts peak-to-peak differential. Head output 132 represents the simulated output of a targeted HDA and its pre-amp. Grey codes are held in a separate RAM and are loaded from the TRACKNUM file for embedded servo track data generation. They are substituted for the specially coded dummy pattern elements in the TRACK.TYP file. 
     For a closed loop operation mode, either an analog or digital position input from a drive electronics board is needed at inputs 134 or 136, respectively. If the digital input 136 is used, it is externally latched between examples. The eight bit digital signal is converted to analog. Filter 82 has characteristics that are selected via menus presented to the user to match the characteristics of the target HDA positioner mechanism. Two resonances, two poles plus a flexed pole at zero, one zero and filter gain are selectable. The conditioned analog position signal is fed to the position pulse generator 84, which produces up/down pulses proportional to the magnitude, direction and rate of change of the incoming positioner signal. The output of the position pulse generator 84 goes to the radial position counter 86. The remainder of the operation is about the same as in the open loop case, above. 
     In FIG. 5, filter 82 is seen to comprise an analog positioner input buffer 170, an input source selector 172, a digital positioner input DAC 174, a resonance one unit 176, a resonance two unit 178, a pole one unit 180, a pole two unit 182, a pole three unit 184, a zero unit 186, and a summing and filter gain stage 188 that produces signal 160. Selector 172 is able to chose between an analog input from the target drive board at buffer 170 and a digital input from the target drive board at DAC 174 because DAC 174 converts the digital input to an analog voltage. Programmable internal analog electronic circuits simulate characteristics for closed loop operation. The parameters associated with two poles, two resonances, one zero, and overall gain are specified via menu selections and ultimately set resonance one unit 176, resonance two unit 178, pole one unit 180, pole two unit 182, pole three unit 184, zero unit 186, and summing and filter gain stage 188. 
     Support features include a trajectory plot function that is preferably also available in the closed loop mode. PC/AT CPU 92 reads the output of radial position counter 86 at pre-determined intervals, thus plotting position versus time. 
     In FIG. 6, an analyzer 190, which implements the analyzer function referred to above, provides frequency response plots of circuit input versus output and is typically used to plot the response of the positioner simulation filter 82. Analyzer 190 comprises an amplitude control DAC and reference 191, a DAC 192, an output amplifier 194, an output director 196, an input selector 198, an input buffer 200, a bus buffer 202 connected to bus 99 and CPU 92, an analog-to-digital converter (ADC) 204, and a level control DAC and reference 206. A signal 208 is used as the input to the positioner simulation filter 82, a signal 210 provides the external measurement stimulus, and a signal 212 outputs the runout offset. A pair of inputs 214 and 216 receive an output of the positioner simulation filter 82 and the external measurement input, respectively. External measurements are also accommodated, via differential output (simulation) and input (circuit response). PC/AT CPU 92 simultaneously scales the analyzer stimulus amplitude and the analyzer input level, which are both dynamically scaled to get the maximum measurement without distortion. The characteristics of the input signal are monitored and the DAC 192 and ADC 204 gains and reference levels are adjusted. Stimulus generator 90 synthesizes an analog frequency-stepped sine wave that is digitally constructed by PC/AT CPU 92. Upper, lower and interval frequency range limits are selected from a closed-loop menu presented to the user (e.g., by display 70), PC/AT CPU 92 steps through the user selected range and sets the signal amplitude with DAC 192. Stimulus generator 90 generates runout, for both open and closed loop modes of operation. ADC 204 has its base level dynamically shifted by PC/AT CPU 92 through DAC 206, to guard against clipping of the input signal. Random noise can be inserted into shaper 116 from either an external source or noise generator 128. Write data from the drive electronics is captured digitally by acquisition unit 118. The write gate signal 140 is monitored separately as the acquisition event trigger. Any acquired data, which is synchronous with index, is injected into the output of the track generators 110 and 112. Up to one full track of write data can be captured. The internal variable clock 104 will ramp up and down to simulate spindle start/stop. The acceleration and deceleration rates for this are entered by the user in the SETUP file. The rate changes are also linked to a proportional amplitude change. This is implemented by an output from DAC 100 that controls the position-proportional summing stage 114 during simulated spin-up/spin-down cycles. The spindle motor simulator 120 accepts motor driver inputs from the drive board and outputs sequenced and delayed feedback pulses. Hall-output equivalent pulses are also preferably available. Signals from internal clocks 102 and 104 can be synchronized to a selected phase of the output of the spindle motor simulator 120. Interface control 122 provides a communication and control link to the drive board with an ST506, an ESDI, a SCSI or an AT-type interface. As such, complete stand-alone drive board testing is facilitated. Multi-board I/O multiplexer 130 allows up to ten drive boards to be simultaneously connected to HDA simulator 80 to enable volume production testing of the drive boards. Appropriate analog and digital multiplexers connect the required drive I/O points to HDA simulator 80. A pre-programmed set of test sequences preferably perform pass-fail tests on each drive board. 
     Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.