HP OpenVMS I/O User’s Reference Manual: OpenVMS Version 8.4 > Chapter 3 Magnetic Tape Drivers

3.2 Magnetic Tape Driver Device Information

You can obtain information on all magnetic tape device characteristics by using the Get Device/Volume Information ($GETDVI) system service. (See the HP OpenVMS System Services Reference Manual.)

See the Help files for more information on the $GETDVI system service.

$GETDVI returns magnetic tape characteristics when you specify the item codes DVI$_DEVCHAR, DVI$_DEVCHAR2, DVI$_DEVDEPEND, and DVI$_DEVDEPEND2. Tables Table 3-1, Table 3-2, and Table 3-4 list these characteristics. The $DEVDEF macro defines the device-independent characteristics, the $MTDEF macro defines the device-dependent characteristics, and the $MT2DEF macro defines the extended device characteristics. The extended device characteristics apply only to the TU81-Plus tape drive.

Table 3-1 Magnetic Tape Device-Independent Characteristics

Characteristic[1]

Meaning

 Dynamic Bits (Conditionally Set)

DEV$M_AVL

Device is on line and available.

DEV$M_FOR

Volume is foreign.

DEV$M_MNT

Volume is mounted.

DEV$M_RCK

Perform data check on all read operations.

DEV$M_WCK

Perform data check on all write operations.

 Static Bits (Always Set)

DEV$M_FOD

Device is file-oriented.

DEV$M_IDV

Device is capable of input.

DEV$M_ODV

Device is capable of output.

DEV$M_SQD

Device is capable of sequential access.

DEV$M_WBC[2]

Device is capable of write-back caching.

[1] Defined by the $DEVDEF macro.

[2] This bit is located in DVI$_DEVCHAR2.

 

Table 3-2 Device-Dependent Information for Tape Devices

Characteristic[1]

Meaning

 

MT$M_LOST

If set, the current tape position is unknown.

MT$M_HWL

If set, the selected drive is hardware write-locked.

MT$M_EOT

If set, an end-of-tape (EOT) condition was encountered by the last operation to move the tape in the forward direction.

MT$M_EOF

If set, a tape mark was encountered by the last operation to move the tape.

MT$M_BOT

If set, a beginning-of-tape (BOT) marker was encountered by the last operation to move the tape in the reverse direction.

MT$M_PARITY

If set, all data transfers are performed with even parity. If clear (normal case), all data transfers are performed with odd parity. Only nonreturn-to-zero-inverted recording at 800 bits/inch can have even parity.

MT$V_DENSITY MT$S_DENSITY

Specifies the density at which all data transfer operations are performed. Possible density values are as follows:

 

MT$K_GCR_6250

Group-coded recording, 6250 bits/inch

 

MT$K_PE_1600

Phase-encoded recording, 1600 bits/inch

 

MT$K_NRZI_800

Nonreturn-to-zero-inverted recording, 800 bits/inch

 

MT$K_BLK_833

Cartridge block mode recording[2]

MT$V_FORMAT MT$S_FORMAT

Specifies the format in which all data transfers are performed. A possible format value is as follows:

 

MT$K_NORMAL11

Normal PDP-11 format. Data bytes are recorded sequentially on tape with each byte occupying exactly one frame.

MT$_FASTSKIP_USED

If set, the most recent IO$_SKIPFILE function was performed using the optimized SCSI space-by-file-marks algorithm. (See “Skip File” for more information about the IO$M_ALLOWFAST modifier to the IO$_SKIPFILE function.)

[1] Defined by the $MTDEF macro.

[2] Only for the TK50 and TZ30 tape drives.

 

Table 3-3 Device-Dependent Information for Tape Devices

Characteristic[1]

Meaning

 

MT2$V_WBC_ENABLE

If set, write-back caching is enabled for this unit.
MT2$V_RDC_DISABLEIf set, read caching is disabled for this unit.

[1] Defined by the $MT2DEF macro. Only for the TU81-Plus. Initial device status will show both of these bits cleared; write-back caching will be disabled, read caching will be enabled.

 

DVI$_DEVTYPE and DVI$_DEVCLASS return the device type and class names, which are defined by the $DCDEF macro. DVI$_DEVBUFSIZ returns the buffer size. The buffer size is the default to be used for tape transfers (normally 2048 bytes). The device class for magnetic tapes is $DCTAPE, and the device type is determined by the magnetic tape model. For example, the device type for the TA78 is DT$_TA78; for the TA81 it is DT$_TA81.

This function code takes no function-dependent arguments.