Reading Non-Standard Tapes on Tape Drives

This invention relates to a magnetic tape drive, and more particularly, to a tape drive which can read tapes written in non-standard formats, as well as a standard format tape.

U.S. Pat. No. 4,863,114--Moeller, et al shows a mini-cartridge in which magnetic tape stores computer data. Small tape drives for writing and reading data stored on 1/4-inch tape in these mini-cartridges are commonly used in personal computer systems. U.S. Pat. Nos. 3 526,371--Blackie et al; 3,924,823--Cohen, et al; 4,647,994--Irwin, et al; and 4,984,111--Rudi are examples of drives utilizing this type of data cartridge.

Quarter-Inch Cartridge Drive Standards Inc. 311 East Carillo Street, Santa Barbara, Calif. 93101 publishes development standards adopted by several manufacturers for this type of disk drive. These standards describe an 80/120 megabyte, 28-track, 14,700 bpi (579 bmm) MFM-encoded flexible disk controller compatible recording format using a 1/4-inch mini-data cartridge. Published standards include "FLEXIBLE-DISK-CONTROLLER-COMPATIBLE RECORDING FORMAT FOR INFORMATION INTERCHANGE", QIC-80 Revision D, 6 Dec. 1989 and "COMMON COMMAND SET INTERFACE SPECIFICATION FOR FLEXIBLE DISK CONTROLLER BASED MINICARTRIDGE TAPE DRIVES", QIC-117, Revision B, 6 Dec. 1989. These published standards are incorporated herein by reference. Companies which make tape drives for reading and writing tapes to these standards include:

Similar tape drives are available which write tapes in a format which is not compatible with the QIC standards. One example of such a drive is that manufactured by Irwin Magnetics, Inc. U.S. Pat. Nos. 4,646,175; 4,586,094--Chambors, et al and 4,498,129 describe the tape drive and format of tapes written on these drives.

In accordance with the present invention, a magnetic tape drive reads both standard and non-standard tapes. A determination is made as to whether a non-standard tape is present. If so, the magnetic head is preset by first moving the magnetic head toward the edge of he tape. When no data is sensed, indicating the edge of the data, the head is moved to the center of track 0.

More specifically, the load zone of the tape is first read to determine whether the tape is written in a standard or a non-standard format. If the format appears to be non-standard, the head must be preset to a reference track, for example, track 0. In order to do this, the head is moved toward the edge of the tape, while reading the successive tracks. The edge of the data tracks is identified when no data is read. Thereafter, the head is moved a known distance from the edge of the tape to a specified track, for example, track 0.

It is an object of the present invention to provide for reading of both standard and non-standard tapes without changing the electronics or the physical characteristics of the drive. Only changes in the tape drive firmware are required to practice the invention.

In accordance with the present invention, non-standard tapes can be read by generating an index pulse at the beginning of each segment. For non-standard tapes, this is accomplished by disabling the index pulse generator while non-relevant, servo, information is detected in the spaces between segments.

In accordance with still another aspect of the invention, tapes having different non-standard formats can be read.

FIG. 1 shows a tape drive of the type in which the present invention is incorporated;

FIG. 2 is a block diagram showing the tape drive of the present invention configured in a computer system;

FIG. 2A depicts the firmware and the interface for a tape drive in which the present invention is incorporated;

FIG. 3 depicts the format of a QIC tape;

FIG. 4 depicts the format of an Irwin tape;

FIG. 5 shows the data signal and the GAP DETECT signal for an odd numbered track on an Irwin drive;

FIG. 6 shows the layout of the data segments in a QIC format;

FIG. 7 shows the layout of data segments in an Irwin format;

FIG. 8 shows the data signal and GAP DETECT signal for another odd track of an Irwin formatting tape;

FIG. 9 shows the data signal and the GAP DETECT signal for an even track on an Irwin formatted tape;

FIG. 10 shows the read signal and GAP DETECT signal for another eve track of an Irwin formatted tape;

FIG. 11 is a flow chart showing the firmware for initializing the tape drive including centering the head on track 0;

FIG. 12 is a flow chart of the firmware for reading Irwin tapes;

FIG. 13 is a flow chart of the firmware for performing SKIP commands; and

FIG. 14 is a flow chart of the firmware for detecting different Irwin formats.

A specific example illustrating the invention shows the changes needed in the firmware of a tape drive which will read QIC tapes. In accordance with the invention, these changes make the drive capable of reading both standard QIC written tapes and tapes written in the non-standard IRWIN format. As an introduction, the following signals and terms are defined.

FIG. 1 depicts a tape drive having a magnetic head 10 which is moved across a magnetic tape 11 in steps by a stepping motor 10a. Tape 11 moves between the reels in a cartridge 12. As the head moves across the tape, it reads data on the longitudinal tracks of the magnetic tape 11.

FIG. 2 shows the tape drive 13 in a typical configuration of a personal computer system. The system includes a host computer 14 and a controller 15. Controller 15 is typically capable of operating peripherals, such as the floppy disk drive 16. The controller 15 is connected to tape drive 13 through an interface 17. In the example under consideration, the interface 17 is specified by the aforementioned QIC117 standards. Tape drive 13 has firmware 18 which performs the operations required to meet the aforementioned QIC80 and QIC117 standards.

The significant parts of the firmware 18 are depicted in FIG. 2A. FIG. 2A also depicts the relevant commands and status indications in the interface 17 and the relevant routines performed in the floppy disk controller 15.

In response to a SEEK LOAD POINT command (or a SOFT RESET command) the PRESET TAPE AND SEEK BURST routine 19 in the firmware presets the head and tape to the reference track on the tape. This is track 0 in the QIC format. When this routine detects a non-standard, i.e., an IRWIN tape, the routine also presets the head to track 0. However, the procedure is quite different as will be explained.

When the routine 19 has preset the tape, it issues a READY status. The software in floppy disk controller 15 then issues a REPORT STATUS command. Firmware 18 has a REPORT STATUS RESPONSE routine 25 which generates a CARTRIDGE REFERENCED byte.

The floppy disk controller 15 issues a REPORT DRIVE CONFIGURATION command in response to the CARTRIDGE REFERENCED byte. The REPORT DRIVE CONFIGURATION routine 26 indicates the format of the tape.

If the appropriate status bit is set to 1, a QIC 80 mode tape has been detected. If this bit is a 0, there is an indication that a QIC 40 mode has been detected. In accordance with the present invention, a status bit is also set to indicate when a non-standard format (i.e., IRWIN mode) has been detected.

The software in floppy disk controller 15 then issues a LOGICAL FORWARD command to interface 17. The logical forward routine 27 in the firmware 18 starts the capstan motor 28 at the appropriate speed. LOGICAL FORWARD routine 27 also enables the read/write electronics 21 after the motor is at speed. This enables the reading of data from the head 10 by the read/write electronics 21. This data is supplied to the CPU through the floppy disk controller. The read/write software in the floppy disk controller issues the proper commands to store data in the buffers and perform other operations on the data.

Software in the floppy disk controller issues a STOP command and in response thereto, the STOP TAPE routine 29 stops the capstan motor 28. This continues until the end of tape at which time the LOGICAL FORWARD routine 27 issues a DONE status.

The gap detect electronics 20 in a QIC drive control the reading of data by generating index pulses at the beginning of each data segment, as will be subsequently described. Read electronics 21 produces a DATA signal as the magnetic head 10 reads the tape. The GAP DETECT electronics produces a signal which is the envelope of the DATA signal. When reading a QIC format tape, an index pulse generator 22 produces an index pulse each time data is detected. This marks the beginning of a data segment.

In accordance with the present invention, the reading of IRWIN formatted tapes is facilitated by disabling the index pulse generator 22 when servo information, which exists in gaps between data segments in Irwin tapes, is detected.

In response to PAUSE and SKIP commands from the software in the floppy disk controller 15, the firmware 18 performs PAUSE and SKIP routines 24. These routines are performed when there is a need to recover, or change tracks. These routines will enable the capstan motor 28 and enable the index generator 22. When the proper number of segments has been counted, the routines 24 issue a DONE (READY) status to the floppy disk controller.

In accordance with the invention, the firmware 18 is also modified so that the drive will perform a SKIP routine 24 on IRWIN formatted tapes. This is a command that is required by the QIC 11 standard and should perform with both the QIC standard tapes or Irwin.

QIC machines also have the capability of correcting the position of the head when errors are caused by positioning of the head with respect to the tape track. When such errors are detected, the MICRO STEP SEEK HEAD routines 23 act through stepper motor 10a to adjust the position of head 10 with respect to the track.

FIG. 3 depicts the layout of a QIC-formatted tape. Two physical holes 30 and 31 in the tape mark the beginning of tape (BOT). Another hole 32 marks the load point (LP). Between the BOT and the LP is a load point zone. Between the load point 32 and the warning hole 33 is 205' of tape upon which data is written. This referred to as the DATA ZONE.

Track 0 has a forward reference burst at 34 in the load zone. Track 3 has a reverse reference burst at 35 in the load zone. These reference bursts are described on page 10 of "QIC DEVELOPMENT STANDARD FLEXIBLE DISK CONTROLLER COMPATIBLE RECORDING FORMAT FOR INFORMATION INTERCHANGE", QIC-80 6 Dec. 1989. In the QIC format, all of the even tracks are written above track 0 and are referenced to track 0. All of the odd tracks are written below track 0, and all odd tracks are referenced to track 3. The firmware of a QIC tape drive has a SEEK BURST routine which, during initialization of the drive, finds the reference bursts on track 0 and centers the head on track 0. When the head is on track 0, the firmware indicates a CARTRIDGE-REFERENCED status through the QIC 117 interface to the host computer. If no reference bursts are found during the performance of the SEEK BURST algorithm, the firmware of a normal QIC-compatible machine will report one of the other statuses shown at page 7 of QIC DEVELOPMENT STANDARD, "COMMON COMMAND SET INTERFACE SPECIFICATION FOR FLEXIBLE DISK CONTROLLER BASED MINI-CARTRIDGE TAPE DRIVES", QIC 117, Rev. B, 6 Dec. 89. This will be in response to a REPORT DRIVE STATUS command from the host. Bit 7 in Table 2(c) is set to a 1 if a QIC 80 mode is detected. This bit is not set if a QIC 40 format is detected.

FIG. 6 depicts the layout of the data segments in a QIC format. In the QIC format, there are 100 data segments each including 32 sectors and each sector has 1024 bytes. Between the segments, are 20 millisecond gaps. An index pulse is generated at the beginning of each data segment for use by the host computer in reading data. The index pulse is generated by reading the GAP DETECT signal, which is the envelope of the DATA signal. In a normal QIC drive the index pulse is generated each time the GAP DETECT signal makes a transition from no data to data.

FIG. 4 depicts the format of the IRWIN tapes. The 32 tracks are consecutively numbered from 0-31, extending from edge to edge of the tape. (Tracks are numbered from 0-19 in the Irwin 40 format to be discussed later). Very little, if any, unrecorded space exists between the tracks. At each edge of the tape, there is a narrow gap, indicated at 36, of unrecorded tape.

A more complete description of the IRWIN format is given in the aforementioned patents assigned to Irwin Magnetics, Inc.

FIG. 5 shows the signal read from a typical odd track, in this case track 1. A servo burst 37 is between data segments on the tape. FIG. 5 also shows the track identification information 38 comprising five bits recorded as a narrow burst for a zero and a wide burst for a one. FIG. 5 shows the identification (I.D.) for track 1 which is 00001. FIG. 5 also shows the GAP DETECT signal 29 for track 1. This signal is the envelope of the data signal and is used in producing the index pulse in accordance with the invention.

The format of the Irwin 80 data is shown in FIG. 7. There are 86 data segments on a typical tape written in the Irwin 80 format. Each segment has 32 sectors, 1024 bytes in each sector, and 32 tracks per tape.

Between segments on the Irwin tape, servo information is written. This servo information is used to control the heads on Irwin machines in order to keep the head on track. Because of the presence of this servo information, an index pulse cannot be generated at the beginning of each data segment in the normal manner that this is accomplished in QIC drives.

The SEEK BURST routine in a QIC tape drive's firmware is modified to place the head on the reference track (track 0) when a QIC or an Irwin format is detected. FIG. 11 is a flow chart depicting the steps. The following steps are performed.

Rewind the tape to BOT.

Get the head to home position (place the head on tape).

Search for reference bursts in the load zone. If a reference burst is detected, the flag 41 is set to YES. This indicates that a reference burst was detected in the load point zone. The head is centered on the bursts (step 42) and an indication that a QIC format has been detected is applied to the interface (step 43).

If no reference burst is detected, go to step 44. Displace 18 feet of tape at 34 ips into the DATA ZONE. The 18 feet of tape displacement in the data zone is done to avoid the long erased gap at the beginning of the tape that is mentioned above (104 inches of erased tape at the start of track). Also, the beginning of the servo burst information would be avoided (862 msec of Irwin servo information at start of track).

While moving the tap at 34 ips, look for 800 msec of consecutive no data readings. This is step 45. This is done to avoid detecting servo information in erase gaps. The 800 msec timeout was chosen to avoid detecting erased tape in between the data segments (Irwin servo information).

Each time DATA is detected, within the 800 msec window, go to step 46. Move the head one step (0.25 mils) down.

When 800 msec of erased tape is detected, go to the step 47. The routine assumes that the lower edge of the data (bottom track) is detected. If data was detected before, as determined by step 47, an Irwin format is indicated (step 48).

Step 49 moves the head a fixed number of steps to the center of track 0.

Rewind to BOT at 100 ips.

Indicate CARTRIDGE REFERENCED status to the QIC 117 host.

Indicate IRWIN MOD status through the QIC 117 interface to the host. This status is indicated by setting bit 0 defined in Table 2(c) on page 7 of QIC-117, "COMMON COMMAND SET INTERFACE SPECIFICATION FOR FLEXIBLE DISK CONTROLLER BASED MINICARTRIDGE TAPE DRIVES", Rev. B, 8 Dec. 1989. This bit was reserved for future use. The status is reported in response to the REPORT DRIVE CONFIGURATION command.

The SEEK HEAD TO TRACK routine will step the head to the QIC 117 host requested track. Normally, the SEEK HEAD TO TRACK ROUTINE steps the head to the requested track by looking at the QIC 80 (QIC 40) flag. The stepping is done per the QIC 80 (or QIC 40) standard with the addition of the Irwin format to the drive. The fixed number of steps between the centers of Irwin track and the track layout is determined. The SEEK HEAD TO TRACK ROUTINE is changed so that when the host requests a track change, and the drive and host are both in the Irwin format, the drive will change its track position according to the Irwin format track layout. In response to an Irwin mode status, this routine places the head at track 0, 1, 2 . . . up to track 31, going from the lower end of the tape to the upper end of the tape, with 30 steps in between tracks (0.25 mils per steps.) (In the Irwin 40 format, there are 20 tracks numbered 0 to 11. The number of steps is 46 instead of 30.)

FIG. 5 shows the "GAP DETECT" input from the read electronics. The firmware uses the "GAP DETECT" signal to count transitions of the servo burst. The transition is validated with a 0.5 msec. timeout, that insures that no "glitches" are detected as a transition.

In order to read the Irwin tape, the servo pattern used by Irwin to position the head on track is masked from the floppy controller, and the index pulse is inserted at the beginning of the segment. This operation avoids giving the floppy disk controller (FDC) an index pulse for the servo information that is in between the segments.

The firmware on a QIC drive was modified as shown in FIG. 12.

When an Irwin tape has been detected, each time the GAP DETECT signal shows the presence of data, the index pulse generator is disabled, as indicated at 50. Flag 51 is set in accordance with whether the tape is starting from the beginning of the track or in the middle of data segments. If starting from the beginning of the track, it is necessary to skip the servo burst which occurs in the first 16 or 17 feet of the tape. On the Irwin tapes, servo information is written in with two transitions of NO DATA to DATA or odd tracks and three transitions of NO DATA to DATA for even tracks. The two transitions 70 and 71 are shown in FIGS. 5 and 8 for odd tracks and the three transitions 72, 73 and 74 are shown in FIGS. 9 and 10 for even tracks. The step 52 looks for these sequences of transitions. In order to timeout the long burst of servo information at the beginning of the tape, these transitions are counted 37 times by step 52. After 37 detections of such transitions, the flag 53 is set to YES. This indicates the first data segment is detected.

In response to this YES indication, the step 54 clears the flag 51 so there is no longer an indication that the drive is starting from the beginning of a track. Also, the index pulse generator is enabled, as indicated by step 55. This enables the generation of an index pulse indicating the start of the first data segment.

The next time the gap detect signal indicates a transition from NO DATA to DATA, the index pulse generator is disabled again as indicated at 50. This time, the flag 51 will indicate that the drive is not starting from the beginning of tape. Between data segments, the Irwin tapes have an ERASE GAP 75, which is relatively short compared to the much longer gap between data segments on standard QIC formatted tape. The ERASE GAP on the Irwin tapes is approximately 10 milliseconds long. (at 40 ips.) The ERASE GAP is indicated at 75 in FIGS. 5, 8-10. An ERASE GAP precedes the servo information. This ERASE GAP is detected as indicated at step 56 in FIG. 12. Then, the remainder of the time interval between data segments is timed out. This is done by counting the data transitions in the servo information by the step 57. This is done to bypass the servo information between the data segments. Two transitions of NO DATA to DATA occur for odd tracks and three such transitions for even tracks. After this burst of servo information, the index pulse generator is enabled, as indicated at 55.

In summary, the following steps are performed:

If starting from the beginning of track: avoid the 2596 msec of erased tape, looking for the first data detection from the GAP DETECT electronics;

Timeout 870 msec which avoids the start of track servo pattern. This is done by counting 37 transitions of data to no data.

Enable index pulse generation.

If in the data portion of a track: look for 10 msec of consecutive erased tape (see FIG. 8 for odd tracks and FIG. 9 for even tracks erased gap). generate an index pulse after the servo transitions.

The above continues until the logical end of track, or until a STOP command is received from the QIC 117 interface.

The head positioning servo data used by Irwin to position its read head to the center of the track, is completely ignored by the drive of the present invention.

The firmware in the drive of the present invention would avoid moving the head while the user's software is reading data, unless instructed by the user's software to do so. The MICRO STEP PAUSE command (QIC 117 specifications) allows the user's software to recover a read error, by stepping the head, and retrying the read until the data is recovered. This compensates for the inaccuracy of the head placement that is a result in variations between track positions on the IRWIN tapes.

FIG. 13 shows the modification in the firmware which will perform a SKIP SEGMENT command from the QIC 117 interface.

A flag 60 is set in accordance with whether the firmware is looking for a GAP. If it is, a determination is made as to whether 10 msec of GAP is sensed, as indicated by flag 61. If 10 msec is not sensed, the loop is repeated until 10 msec of GAP is sensed, thereby getting a YES indication from flag 61. This means that the tape is at a position where the head is about to read a data segment. As indicated at 62, the firmware is set so that it is looking for data. This flips the flag 60 to the NO condition. It also decrements the counter 63 by one count. Counter 63 is set with the number of data segments which are to be skipped. It counts the erased gaps 35 of the servo bursts which are between segments. Assume the command is SKIP 10 FORWARD. This counter is set to ten and is decremented each time a data segment is counted. During normal reading of a QIC tape, the counter is decremented each time there is an index pulse. When reading Irwin tapes, the counter is decremented each time there is a servo burst in between segments. When the counter is decremented to zero, there is an exit indicating that the number of specified segments have been counted.

If counter 63 is at other than 0, a NO indication, the loop is repeated.

The routine returns to the beginning of the loop. This time, the flag 60 will indicate that the firmware is not looking for a GAP. The flag 64 is looking for ten msec of data. If ten msec of data is found, a YES indication, then the step 65 resets the flag 60 to "looking for a gap". If the flag 64 does not detect 10 msec of data, a NO indication, the firmware continues to look for 10 msec of data.

In this way, the number of data segments through which the head reads is counted until the specified number of data segments has been skipped.

In accordance with a modification of the invention, the reading of different formats of non-standard tapes may be accomplished. For example, Irwin tapes are written in both an Irwin 40 format for 40 megabyte drives and an Irwin 80 format for 80 megabyte drives. What has been described thus far is for an Irwin 80 format. The Irwin 40 format differs in the number of sectors per segment, 18, whereas Irwin 80 has 32 segments; in the number of segments per track, 124, whereas Irwin 80 had 86 segments; the number of tracks per tape, 20, whereas Irwin 80 had 32; and in the track spacing, 11.6 mils, whereas Irwin 80 had 7.25 mil spacing.

In order to read Irwin 40 tapes, it is only necessary to change the tape speed and to obtain correct presetting on track 0. Both of these can be done by the detection of Irwin 40 tapes, which in accordance with the invention, is accomplished by detecting the difference in the length of the data segments in the Irwin 40 format as opposed to Irwin 80 tapes.

The Irwin format detection routine, which is a part of the Seek Burst routine, is changed. This is so that the drive's firmware is able to indicate to the user's software the presence of an Irwin 40 or an Irwin 80 tape in the drive. Also, since the track width of the Irwin 40 format is different from the track width of the Irwin 80, the firmware needs an indication to know when to correct the track center point.

FIG. 14 is a flow chart which is a modification of the flowchart of FIG. 11. FIG. 14 describes the firmware for reading both of the Irwin formats.

The routine starts by scanning the load point zone for QIC type reference burst as indicated by flag 70. If those bursts are found, the routine centers on the track 0 reference burst (step 71), and indicates the appropriate QIC format to the user (step 72), as described with reference to the Report Drive Configuration command of the QIC 117 standard.

If the QIC reference bursts are not detected, the step 73 starts the tape at 34 ips from BOT, and displace 18 feet of tape in the data zone.

At this point, the routine determines whether the tape contains data in the data zone (in which case it might be an Irwin tape), or whether the tape is not formatted at all. The step 74 looks for 10 msec of consecutive DATA detect from the GAP DETECT signal. If there are 256 consecutive samples of NO DATA at 0.5 msec intervals, the step 75 indicates that the tape is not formatted at all. If the tape was not formatted, the routine clears the CARTRIDGE REFERENCED flag in the REPORT DRIVE STATUS byte of the QIC117 standard and exits.

When the routine concludes that the data zone contains data, it tries to find the bottom edge of the lower track on the tape (on the Irwin tapes this is track 0). This is done by step 76 which moves the head in 0.25 mils steps, until 900 msec of consecutive NO DATA detection is timed out. Flag 77 indicates YES when the 900 msec interval is timed out.

At this point, the routine detected the bottom edge of the lower track on the tape, but the type of format on the tape is an unknown. Therefore, the routine does not know to what point to step the head in order to center on track 0. For now, the step 78 indicates that the IRWIN MODE is detected (bit 1 of the REPORT DRIVE CONFIGURATION byte).

In order to detect the tape format, the routine takes advantage of the fact that the segment on the Irwin 80 format is longer than the Irwin 40 segment (32 sectors compared to 18 sectors respectively). Running at 40 ips, the segment length of the Irwin 80 format would be approximately 580 msec long, and for the Irwin 40 approximately 380 msec long.

The step 79 assumes that the tape is an Irwin 80 tape, therefore, clearing the flag which indicates Irwin 40 (REPORT DRIVE CONFIGURATION byte, bit 2), and stepping the head a fixed number of steps (31), to the center of track 0, to what is assumed to be track 0 of the Irwin 80 tape. The tape is started at 40 ips, and the segment length is measured by the step 80. If the flag 81 indicates YES, the length of the segment was found to be less than 480 msec long (middle point between 380 msec segment length and the 580 msec segment length), the tape is considered to be an Irwin 40 tape. The step 82 adds 17 more steps to the 31 steps that it steeped already for the Irwin 80 tape (total of 48 steps), so that the center line of track 0 on the Irwin 40 tape would be corrected. The Irwin 40 flag is set, and the routine is complete. If the length of the segment was found to be equal or greater than 480 msec, the routine is complete (the head is already at the center of the Irwin 80 track 0, and the Irwin 40 flag is cleared).

The Logical forward Irwin 80 routine does not have to change to accommodate the Irwin 40 format, only tape speed is changed from 40 to 50 ips when reading Irwin 40 tapes.

The SKIP command algorithm for the Irwin 80 does not have to change to accommodate the Irwin 40 format.

The number of tracks need to be changed from 32 to 20 in the Seek Head to Track Irwin 80 routine, to accommodate the Irwin 40 format.

Changes in the firmware of a QIC 40 or QIC 80 compatible tape drive constitute the preferred way of practicing the invention. For example, this firmware is imbedded in Intel 8051 integrated circuit chips. The programming of these chips is apparent from the user's instructions for these chips and from the foregoing description of the invention.

While a particular embodiment of the invention has been sown and described, various modifications are within the true spirit and scope of the invention. The appended claims are, therefore, intended to cover all such modifications.