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_DISABLE | If 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.