rfc190.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

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


         Function:

            Suppresses the display of the tty simulation display area,
            restores the display of all other display areas, and sets
            wsmode on.

   (RSTDA)    Reset display areas.

      JSYS rstda; [453B]     Reset display areas

         Accepts:

            none

         Returns:

            +1:  Always

         Functions:

            Deallocates and removes images from all display areas
            associated with this console except the tty simulation and
            cursor, the display of which is restored.

(IV)  Message formats.

   Messages are sequences of 8-bit characters, of which 7 contain useful
   information.

      The higer-order (200B) bit should contain even parity on IMLAC
      input and is set to even parity on IMLAC output.

      If the IMLAC receives an odd parity character, it halts at
      present.

      In the remainder of this document, the parity bit will not be
      discussed.

   A message may be either a character or a command.

   Single-character messages from the PDP-10 to the IMLAC represent
   program output intended for the teletype.

   Commands from the PDP-10 represent display information.

   Commands from the IMLAC represent characters or other input
   information.




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


   Every command is prefixed by an internal escape character (code 33B)
   and a character count.

      The escape character will henceforth be referred to as ESC: is has
      the same code as the ASCII escape character 33B.

   Messages sent from TENEX to IMLAC:

      Characters 40B-177B are directed to the teletype simulation area.

      Character 12B (line feed) starts a new line in the teletype
      simulation area.

      An ESC indicates that display or control information is coming, as
      follows.

         Every message beginning with ESC contains the number of
         following characters as its second character.

         Certain constructs appear in several command messages.

            (da)  A display area identifier is a pair of characters
            containing 12 bits of information:

               1st: bits (0:5) + 40B

               2nd: bits (6:11) + 40B

            (NSTRS)  A string count is a single character between 0 and
            177B.

            (STRID)  A string identifier is a single character between 1
            and 177B.

            (RETAIN)  The retention flag, if non-zero, specifies that an
            existing string should be retained rather than overwritten.

            (CSIZE)  A character size is a single character between 0
            and 3:

               The character sizes are respectively x1/2, x1, x2, x3.

            (HINC)  A horizontal increment is a single character.

               In the present implementation, HINC is ignored and a
               standard spacing is supplied as follows.





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


                  LVH:

                     0: 3 units

                     1: 6 units

                     2: 12 units

                     3: 18 units

                  non-LVH:

                     0: 4.5 units

                     1: 9 units

                     2: 18 units

                     3: 27 units

            (FONTS)  A font specification is a single character.

               In the present implementation, the font is stored but
               does not affect the display.

            (outxy)  An output X-Y coordinate pair is encoded in four
            characters as follows:

               1st: X,bits(0:5) + 40B

               2nd: X,bits(6:11) + 40B

               3rd: Y,bits(0:5) + 40B

               4th: Y,bits(6:11) + 40B

            (inxy)  An input X-Y coordinate pair is encoded in four
            characters as follows:

            LVH:  see (outxy) above.

            non-LVH:  as above, except that each 12-bit coordinate is
            actually of the form 1400B+40B*[v/9]+(v MOD 9), where the
            actual coordinate is 0<=v<=719.

                  This means there are actually fewer points on each
                  axis.




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


            (string)  A string is just the requisite number of
            characters.

               Control characters will be displayed as a distinctive
               blot.

         Each display operation has a corresponding message.

            01B - ADA (assign display area)

               Followed by (da) NSTRS CSIZE HINC FONT.

            02B - DDA (delete display area)

               Followed by (da).

            04B - STRDA (string display)

               Followed by (da) STRID RETAIN (xy) FORMAT [CSIZE] [HINC]
               [FONT] (string).

                  Format specifies whether each of CSIZE, HINC, and FONT
                  is to come from the display area default, the current
                  value for the string, or the message.

                     The bits are: 0 0 STF STI STC RDF RDI RDC.

                     RDF=1 means read the FONT from the message.

                     RDF=0, STF=1 means use the old value from the
                     string.

                     RDF=0, STF=0 means use the display area default.

                     The pairs RDI-STI and RDC-STC specify HINC and
                     CSIZE in the same way.

            05B - SCSR (set cursor string)

               Followed by RETAIN CSIZE HINC FONT (string).

            06B - SDDA (suppress display of da)

               Followed by (da) KILL.

                  KILL#0 means delete all strings in this display area.

                  KILL=0 means retain the strings.



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


            07B - RDDA (restore display of da)

               Followed by (da).

            10B - SDDA (suppress display of string)

               Followed by (da) STRID KILL.

                  KILL#0 means delete the string.

                  KILL=0 means retain the string.

            11B - RSLA (restore display of string)

               Followed by (da) STRID.

            12B - TSNDA (turn teletype simulation on)

            13B - TSFDA (turn teletype simulation off)

            14B - Long input mode

               Puts the IMLAC into the mode where it sends coordinate
               information in a message with every character.

                  This is the normal operating mode for the IMLAC.

            15B - Short input mode

               Puts the IMLAC into the mode where it outputs characters
               literally, just like a teletype.

                  The IMLAC starts out in this mode when turned on.

         A string of 10 ESC characters, followed by a non-ESC, indicates
         an emergency - the IMLAC reinitializes itself and goes into
         short input and teletype simulation modes.

      All other (control) characters are ignored.

   Messages sent from IMLAC to TENEX:

      Short input mode:

         Every character typed on the keyboard is transmitted literally.






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


      Long input mode:

         Every message begins with ESC and a count of subsequent
         characters.

            Codes 40B-177B represent keyboard input.

               Note that the IMLAC does not echo these characters on the
               display.

            Codes 00B-37B, except ESC, represent typed-in control
            characters.

               The present implementation allows the user to generate
               all of these codes from the keyboard.

            ESC may be followed by a keyset-mouse code or a control
            character.

               Code 00B represents an ESC typed on the keyboard.

               Otherwise, a code 40B-77B and a code 100B-107B follow.

                  This type of message is sent whenever the mouse
                  buttons change or a character has been typed on the
                  keyset, and the IMLAC cannot convert this to an
                  ordinary character.

                     The IMLAC converts recognizable keyset chords and
                     mouse changes to characters; see SRI-ARC
                     documentation for a full discussion of this
                     hardware.

                  The codes 40B-77B represent accumulated keyset chords.

                     40B means no complete chord has been struck.

                  The codes 100B-107B represent the state of the mouse
                  buttons after a change:  a 1-bit corresponds to a
                  depressed button.

               Other codes should not appear.

            All codes are followed by the (inxy) coordinates of the
            mouse.

               This means 7 or 8 characters are sent for each character
               typed.



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


(V)  Division of responsibility

   The first criterion in design of the system just described was to
   allocate sufficient validity checking to the PDP-10 to make it
   unnecessary for the IMLAC to send a response for each command.

      Thus, the PDP-10 allocates and checks display area identifiers and
      string numbers.

      In the present implementation, display areas are numbered system-
      wide whereas strings are numbered from 1 to N within a display
      area.

   The only errors not detectable by the PDP-10 are transmission parity
   errors and overflow of the IMLAC's memory.

      The former are presently not corrected, but could be handled by
      any standard technique.

      The latter are in principle detectable by the PDP-10, since the
      amount of space required to store a given display is fairly simply
      computable.

         If the IMLAC runs out of space, it deletes lines from the top
         of the teletype simulation display, until only three are left,
         before giving up.

   A secondary criterion was to hold down the number of characters
   required to represent a display command.

   We have found two problem areas and two areas in which we expect to
   expand the IMLAC's capability.

      Echoing was relegated to TENEX since we desired to avoid the
      well-known complications associated with remote echoing.

      The question of identifying a device as an IMLAC to TENEX gave us
      a great deal of trouble.

         We settled on the convention of a TENEX Executive command which
         causes TENEX to send the "Long input mode" message.

            The IMLAC starts out in short input mode.

         The TENEX character input routines also may be set into either
         long or short mode.

            Their state is changed by the TSNDA and TSFDA system calls.



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


            In short mode, (TSNDA last), short input is passed
            literally, and only the character is passed from long input.

            In long mode (TSFDA last), short input is padded with all-
            zero coordinates, and long input is passed literally.

            This arrangement allows TENEX programs which do not use the
            special features of the IMLAC to operate correctly with
            either an IMLAC or a teletype.

            The user may restore the IMLAC to short mode with another
            command or with a special key on the IMLAC keyboard.

         Code is ready to allow the IMLAC to collect entire literal
         strings with some internal editing before sending them to
         TENEX.

            We have not resolved the disposition of characters typed by
            the user between the typed command initiating literal input
            and the receipt by the IMLAC of the "collect literal"
            message.

         With 8K of core, the IMLAC can handle a significant fraction of
         the command parsing and feedback functions of the SRI-ARC On-
         Line System (NLS), for which this effort is principally
         intended.


             [This RFC was put into machine readable form for entry]
             [into the online RFC archives by Lorrie Shiota, 10/01]





















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