XT(4)

NAME
xt - Xylogics 472 MULTIBUS magtape interface

SYNOPSIS
controller zt0 at mbad? csr 0x0300 maps 34 bin 5 intr 7

DESCRIPTION
The Xylogics 472 and an industry-standard Cipher formatted interface transport combine to provide a standard tape drive interface as described in mtio(4). Zt is the name of the controller, and mt is the name of the drives attached to the controller. Depending on the transport and formatter, speed and density may be selected by various bits in the minor device number. The bits in the minor device number are as follows: The low order two bits select the logical unit. As many as four transports on any combination of controllers and formatters are supported. The next bit, 004, specifies that the tape is not rewound when the associated special file is closed.

The number of MULTIBUS maps specified on the line to config(1) should be at least 10. If a requested I/O operation cannot be mapped due to a lack of MULTIBUS maps, ENXIO will be the returned and a diagnostic message will be printed on the console.

The tape controller must be strapped up for 24-bit addressing.

Note: Closing a no-rewind xt device after reading will not space the tape forward to the beginning of the next file. This behaviour differs from that of the SSM 1/2" tape device (tg).

BINARY CONFIGURATION
When building a kernel with MULTIBUS magtape, be sure that the binary configuration information in /sys/conf/conf_xt.c is up to date. The constants and variables defined in conf_xt.c include:

XTCTLR
    The maximum number of zt controllers supported by the driver.

xtdensel
    Set to one if the tape drive supports density select operations. Some Cipher tape drives only support 1600-bpi operation.

xtunits
    This array (indexed by logical unit from the minor device number) describes the controller and transport assignments that will be supported by the system. Wildcarding may be used to force the driver to probe each controller for the specified tape drives. The example below describes two possible controllers, with two tape drives on each controller.

struct	xt_unit	xtunits[] = {
/*	 ctlr		drive	*/
	{ ANY,		ANY },		/* xt0: any controller, any drive */
	{ ANY,		  1 },		/* xt1: any controller, drive 1 */
	{ ANY,		  0 },		/* xt2: any controller, drive 0 */
	{ ANY,		  1 },		/* xt3: any controller, drive 1 */
};

STANDALONE
Standalone MULTIBUS magtape offers a subset of the facilities offered by UNIX MULTIBUS magtape. In particular, the standalone tape driver does not do density selection on open (the density must be set manually from the tape front panel), and does not do retries on I/O errors.

SEE ALSO
mt(1), tar(1), mtio(4)

FILES

/dev/mt*
    block magtape devices

/dev/rmt*
    raw magtape devices

/sys/conf/conf_xt.c
    binary configuration file

DIAGNOSTICS
xt%d: not enough maps for transfer. A requested transfer is too large to be mapped by the number of Multibus maps allocated to the controller. The number of maps can be increased in the kernel configuration file but this may affect other parts of the Dynix kernel.

xt%d: drive %d ctlr %d conflict. A drive was not wildcarded in the binary configuration, but the specified drive number was already in use (allocated to some previously probed tape device).

xt%d: no write ring. An attempt was made to write on the tape drive when no write ring was present; this message is written on the terminal of the user who tried to access the tape.

xt%d: not online. An attempt was made to access the tape while it was offline; this message is written on the terminal of the user who tried to access the tape.

xt%d: can't switch density in mid-tape. An attempt was made to write on a tape at a different density than is already recorded on the tape. This message is written on the terminal of the user who tried to switch the density.

xt%d: hard error bn%d er=0x%x. A tape error occurred at block bn. The error code is as described in the Xylogics manual. Any error is fatal on non-raw tape; when possible the driver or controller will have retried the operation which failed several times before reporting the error.

xt%d: recovered error bn%d. The controller was able to recover an error while reading or writing.

BUGS
If any non-data error is encountered on non-raw tape, it refuses to do anything more until closed.

Due to a hardware limitation, the xt tape driver cannot tell the difference between a missing tape drive and a tape drive with no tape loaded. As a consequence, tape probing pretends it found all configured tape drives on any controller present in the system. Be careful with wildcarding in the binary configuration.

If a drive supports more than one tape density, the user must manually select the desired tape density while loading the tape.