rfc190.txt

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Network Working Group                                         P. Deutsch
Request for Comments: 190           Xerox Research Center, Palo Alto, CA
NIC: 7135                                                   13 July 1971


                DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM

   This report describes an operational system for communicating textual
   display information between a main-site computer and a remote-display
   processor.

      The main site machine is a DEC PDP-10 with the BBN paging hardware
      (henceforth TENEX).

      The remote machine is a IMLAC PDS-1 (henceforth IMLAC).

      Section (1) briefly describes the IMLAC hardware configurations.

      Section (II) describes the display facilities presented to the
      user.

      Section (III) describes the system calls (JSYS calls) implemented
      in the TENEX monitor to provide these facilities.

      Section (IV) describes the formats of the messages used for
      communication between TENEX and the IMLAC.

      Section (V) analyzes the division of responsibility between the
      two machines.

(1)  Hardware configurations.

   The standard IMLAC is a 16-bit minicomputer with 4K of 2 microsecond
   core, a cycle-stealing display, an input keyboard, and an
   asynchronous serial communication interface.

   The display is normally programmed to draw characters using very
   short vectors.

      The display comes in two major configurations, depending on the
      presence or absence of hardware for drawing long vectors.

      In the sequel, specifications depending on the configuration will
      be flagged LVH or non-LVH respectively.

   The I/O system normally does not provide for interrupts when
   characters arrive from the serial interface.




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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


      However, the IMLAC is barely able to keep up with the PDP-10
      without this feature, so we were able to persuade the manufacturer
      to implement it.

   While no special hardware is required for the software described
   here, the character interrupt and the SRI-ARC "mouse" and "keyset"
   are highly recommended, and the software is oriented towards their
   use.

(II)  Facilities.

   Each display console in the system may be in "display mode" or
   "teletype simulation mode".

      In display mode, the information displayed consists of text
      strings at arbitrary positions on the display face.

      In teletype simulation mode, the display shows the last 20-30
      lines which would appear on a teletype listing.

      A given console may switch between these modes, under program
      control, without losing any information.

   Regardless of mode, each display has a cursor string which follows
   the position of the available pointing device,

      The implemented system uses a "mouse" generally, but one console
      uses a tablet.

      The cursor string may be set by a program, for example to indicate
      at what sort of object the user is expected to point.

   In display mode, the screen of a given console is allocated to users
   in rectangular blocks called "display areas".

      This allows users to communicate via a single display split into
      multiple areas.

   When a user (program) requests a display area, he specifies how many
   text strings he will want to display in it.

      Each string has its own X-Y location, character size, font
      (italic, underline, ...), and an arbitrary number of characters.

         Each of these components is settable without disturbing the
         others.

      Each string may be manipulated without affecting the others.



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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


(III) JSYS calls.

   (ADA) Assign a display area.

      JSYS ada: [440B]     allocate a display area

         Accepts:

         r1:

            upper-left-y-cord[10], upper-left-x-cord[10], max-no-
            string[11]

         r2:

            lower-right-y-cord[10], lower-right-x-cord[10], default-c-
            size[2], default-n-inc[6], default-font[5]

         Returns:

            +1: Unsuccessful

               r1: error code

            +2: Successful

               r1: da-id[18]

         Function:

            This jsys allocates a display area given the coordinates of
            the diagonal, the maximum number of strings to be displayed,
            and the default setting for the character size, font, and
            horizontal increment.  An 18-bit da-id is returned which
            should subsequently be used to refer to this display area.

   (DDA) Deallocate a display area.

      JSYS dda; [441B]     deallocate a display area

         Accepts:

            r1: da-id








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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


         Returns:

            +1: Unsuccessful

               r1: error code

            +2: Successful

         Function:

            This jsys deallocates a display area given the associated
            da-id.

   (STRDA)  STRing display:  add, delete, or change.

   JSYS strda; [442B]     Manipulate (move, write, replace, delete) a
   string in a display area

      Accepts:

         r1: string-id[18], da-id[18]

         r2: first byte pointer or 0 or -1

         r2: second byte pointer or 0

         r4: y-cord[10], x-cord[10], font[6], c-size[3], h-inc[7]

      Returns:

         +1:  Unsuccessful

               r1: error code

         +2:  Successful

               r1: string-id[18]

      Function:

         This jsys writes a new string, replaces, deletes, or moves
         (optionally replacing) an extant string within a display area.
         In addition, the font, character size, and horizontal increment
         may be specified for the string.

            The string may be specified by two byte pointers or by one
            byte pointer with the string terminating with a zero
            character.



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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


               If first byte pointer is zero then

                  if a new string is being written then

                     an error code illstr is returned.

                  Otherwise, the string already exists so

                     delete the string from the display area.

               If the first byte pointer is -1 then

                  if a new string is being written then

                     an error code illstr is returned.

                  Otherwise, use the old string.

               If the first character of the string is a zero character,
               the string to be displayed is null, but the string is not
               deleted.

            The coordinates (optional unless the string is new or being
            moved) are relative to the upper leftcorner of the display
            area.

               If the jsys is to effect an extant string, a zero
               coordinate means use the old value.

            For the font, c-size, and h-inc fields a field of all one's
            indicates that the display area default value (set in the
            ada jsys) is to be used.  A 0 means use the value which was
            previously used for the (extant) string.

            If the string is new, then an 18 bit string identifier is
            returned.

   (SCSR)  Set the Cursor StRing.

      JSYS scsr; [450B]     display a string (vectors later) as the
      cursor

         Accepts:

            r1:  first byte pointer or 0 or -1

            r2:  second byte pointer or 0




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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


            r3: font[5], c-size[2], h-inc[6]

               No defaults allowed

         Returns:

            +1:  Unsuccessful

               r1:  error code

            +2:  Successful

         Function:

            This jsys is used to set the cursor string.  Later, a set of
            vectors will be allowed also.  If the string length is zero
            or the first byte pointer is 0, nothing will be displayed
            for the cursor.  If the first byte pointer is -1 then the
            old string will be used.  If a cursor did not previously
            exist, an illcon error return will be executed.

   (SDDA)  Suppress the display of an area.

      JSYS sdda; [444B]    suppress all display in a display area

         Accepts:

            r1: da-id[18]

            r2:  1 or 0

         Returns:

            +1:  Unsuccessful

               r1:  error code

            +2:  Successful

         Function:

            The display image is removed from the display area but is
            not destroyed if r2 = 0.

   (RDDA)  Restore the display of an area.

      JSYS rdda; [446B]    restore all display in a display area




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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


         Accepts:

            r1: da-id[18]

         Returns:

            +1:  Unsuccessful

               r1:  error code

  +2:  Successful

         Function:

            The display image is restored in the display area.

   (SDDA)  Suppress the display of a String.

      JSYS ssda [445B];    suppress display of a string in a display
      area

         Accepts:

            r1: string-id[18], da-id[18]

         Returns:

            +1:  Unsuccessful

               r1:  error code

            +2:  Successful

         Function:

            The display image for the given string is suppressed in the
            display area

   (RDSA)  Restore the display of a String.

      JSYS rsda; [447B]    restore display of a string in a display area

         Accepts:

            r1: string-id[18], da-id[18]






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RFC 190         DEC PDP-10 -- IMLAC COMMUNICATION SYSTEM    13 July 1971


         Returns:

            +1:  Unsuccessful

               r1:  error code

            +2:  Successful

         Function:

            The display image for the given string is restored in the
            display area.

   (TSNDA)  Teletype Simulation oN.

      JSYS tsnda; [451B]     turn tty simlaution on

         Accepts:

            none

         Returns:

            +1:  Always

               r1:  1 if was in work station mode, 0 otherwise

         Function:

            Restores the tty simulation display area, and suppresses all
            others (except the cursor).  Turns wsmode (work station mode
            flag) off for this console and returns previous value of
            wsmode.

   (TSFDA)  Teletype Simulation ofF.

      JSYS tsfda;  [452B]     turn tty simulation off

         Accepts:

            none

         Returns:

            +1:  Always






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