NAME

gt − ISI SCSI tape driver

SYNOPSIS

GT0 at address 000ffffc0 vector 0x78 level 6
GT0 at ∗∗∗ no address ∗∗∗ no vector

DESCRIPTION

The GT devices provide standard magtape access to a variety of tape storage devices.  They work with different QIC formats, 1/2-inch reel-to-reel, 1/2-inch cartridge, micro-cartridges, 8mm video, etc. 

Because the SCSI-U hardware byte-swaps data, disabling byte-swap (by swapping again in the software) slows down transfers, but allows tapes to be read by other machines.  ISI format enable (together with byte swap) is used to read tapes written by the ISI QIC-2 controller (with variable block sizes).  It can also be used to write ISI format tapes, if a QIC-24 drive is used.  ISI system distribution tapes and diagnostic tapes are written in ISI format and must be read using the isi-swap device.  The ISI format block device is not supported. 

The standalone drivers support all the device types supported by the UNIX driver except for non-rewind devices.  However, it should be noted that only devices scsi_chr_isi_swap_4 and scsi_chr_isi_swap_5 can be used to autoboot or to load the system distribution or diagnostics tapes. 

The flag qi_flags&1 disables the use of disconnect/reconnect, which is enabled on all devices by default. 

The SCSI-U hardware byte-swaps all data sent to devices.  Byte-swapping medium data poses no problem, because the data will be byte-swapped again when it is read from the device, but byte-swapping command data renders commands unintelligible.  Therefore, the SCSI-U firmware automatically byte-swaps command data before sending it to the device, ensuring that it will be read properly after the SCSI-U hardware byte-swaps it again. 

You can control software byte-swapping with two flags: qi_flags&2 and qi_flags &4.  When these flags are set to 0, command data is byte-swapped by the SCSI-U firmware before being sent to the device, but medium data is not. 

Setting qi_flags&2 to 1 disables software byte-swapping of command data.  This flag must be set to 0 when using the SCSI-U. 

Setting qi-flags&4 to 1 enables software byte-swapping of medium data.  The data will be byte-swapped twice, slowing down transfers, but making the stored data readable by other controllers or CPUs. 

The qi-flags&8 flag disables buffering by the tape drive.  By default, the tape drives use buffering, which allows them to stream.  The drawback associated with buffering is that tape write errors cannot be identified until one or more transfers later.  Thus, residual counts on error are not accurate. 

The GT devices also support some additional ioctl calls.  These are listed in <sys/mtio.h>.  Not all calls work with all tape devices. 

FILES

GT Minor Device Number Construction:

bitUNIX functionStandalone function
0-2SCSI target device id numbersame as UNIX function
3-4SCSI bus (SCSI-U controller) numbersame as UNIX function
5disable byte swap (1 = no byte swapping)same as UNIX function
6 enable ISI format (1 = use ISI format)same as UNIX function
7non-rewind (1 = no rewind after close)reserved

The table on the next page lists examples of device names. 

Example Device Names for Controller 0, Device 4:

/dev/tape name/dev linksstandalone
scsi_blk_swap_4mt0-mt8-gt(4,0)
scsi_blk_4smt0-smt8-gt(36,0)
scsi_blk_swap_norew_4nmt0mt4nmt8mt12
scsi_blk_norew_4snmt0smt4snmt8smt12
scsi_chr_swap_4rmt0-rmt8-gt(4,0)
scsi_chr_4srmt0-srmt8-gt(36,0)
scsi_chr_swap_norew_4nrmt0rmt4nrmt8rmt12
scsi_chr_norew_4snrmt0srmt4snrmt8srmt12
scsi_chr_isi_swap_4irmt0-irmt8-gt(68,0)
scsi_chr_isi_4isrmt0-isrmt8-gt(100,0)
scsi_chr_isi_swap_norew_4isnrmt0isrmt4isnrmt8isrmt12
scsi_chr_isi_norew_4inrmt0irmt4inrmt8irmt12

SEE ALSO

gg(4i), mtio(4)

4th Berkeley Distribution  —  15 April 1988