

                                                      May 18, 1985


                          UPDOWN - RT-11 Subdevice Managers


                                    R. W. Barnard
                            Sandia National Laboratories
                         Minicomputer Software Division 7523
                                   P. O. Box 5800
                                Albuquerque, NM 87185
                                   (505) 844-5115

                                    Introduction                                    ____________

              The IND control files DOWN, UP, and HOME can be used to con-
         veniently move among subdevices.  DOWN will mount a subdevice and
         assign DK to that device.  DOWN supports two levels of subdevices
         (i.e., a subdevice within a subdevice).  UP moves back up one sub-
         device.  HOME returns you from wherever you are to SY: as your
         default device.  You can also create a command OVER, which goes
         from one subdevice to another.  The files report the filespec of
         the subdevice file in which you are currently located with the IND
         file CUR.

                                       Useage                                       ______

              These files can be used very effectively with UCL.  Thus, you
         can define

         DOWN == R IND\SY:DOWN ^
         (assuming you are using UCL+... syntax is slightly different for
         the DEC UCL).  To use, you can then just type

         DO[WN] FILESPEC

         Similarly, you can define

         UP == R IND\SY:UP, and

         OVER == R IND\SY:UP\R IND\SY:DOWN ^


              Note that if you are two levels deep in subdevices, and want
         to go OVER to another subdevice located on the subdevice above
         (e.g., LD7), you do not need to specify the device name.  Thus, if
         BIGDSK.DSK has the files DISK1.DSK and DISK2.DSK, and you are cur-
         rently in DISK1, then you may type OVER DISK2, instead of OVER
         LD7:DISK2.

                                      Mechanics                                      _________

              Because of a limitation of IND (which has been SPR'ed) it is
         not possible to relate a file to a logical device assignment (or
         vice versa) from within an IND file.  Consequently, these IND
         files use LD7 for the first level of subdevice, and LD6 for the
                        UPDOWN - RT-11 Subdevice Managers       Page 2



         next subdevice.  Furthermore, when you go DOWN, you are told
         exactly which file is now your default (e.g., DU0:FORTRA.DSK), but
         when you come UP or HOME, IND cannot tell which file you are cur-
         rently in.  It therefore can only report the name of the file, but
         not the device it is on.

              The file DOWN takes as an argument the file you want to go
         down to.  It assumes it to be on DK:, with an extension .DSK,
         unless you specify otherwise.  If you do not specify a file when
         you run DOWN, you will be prompted.

              In order to figure out where it is, the files UP and HOME use
         the volume ID of the disk or subdevice.  The file which reads the
         Volume ID is CUR.COM (CURrent location).  Volume IDs can be done
         in either of two formats - the regular RT format, in which you use
         the 12 characters of the Volume ID for something like FORTRA.DSK,
         or in the DSKLIB format.  The latter program is a means of main-
         taining an on-line catalog of your disks.  It is available as
         DECUS Library program #11-743.  Regardless of the format, CUR
         reports only the file name and extension.  You can define a UCL
         command CUR == TYPE SY:CUR.COM to report your whereabouts at any
         time.
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