CHAPTER 1

                        Terminal Driver Modifications



              This chapter discusses the  modifications  to  the  RSX
         terminal  driver  required  to  support  the security system
         (SCLI) for remote dial-up lines.  



         1.1  Overview

              The RSX-11 (M and M+) terminal  driver  unconditionally
         forces  MCR  to  a terminal being answered on a remote line.
         While intended to provide a consistent interface  to  remote
         terminals,  this  functionality  breaks the security system,
         which depends upon  SCLI  owning  any  protected  terminals.
         Equally  unfortunate is the fact that TTDRV does not use the
         normal SCLI$ mechanism to establish MCR, but instead  simply
         hammers the executive data structures directly.  The exec is
         thus unaware that a port's CLI has changed, and does not in-
         form  SCLI of the action.  This prevents SCLI from re-taking
         the port.  

              Fortunately, a very simple patch to the terminal driver
         will  'correct'  this  situation.   The  remainder  of  this
         chapter describes the modification,  and  includes  instruc-
         tions  for making the patch either in the sources or via ZAP
         to an existing system.  



         1.2  Modification Details

              The relevant code is in subroutine MANS (modem answer),
         in  module TTMOD.MAC.  This file can be found on the distri-
         bution kits in [11,10].  MANS is called when a  remote  line
         is  answered  (e.g.,  carrier  detected).  Its purpose is to
         place the terminal in a known (and benign) state.  MANS mod-
         ifies the terminal characteristics words, sets the buffer to
         72., and forces the CLI to MCR.  It then initiates  autobaud
         (if the terminal is set ABAUD), and returns.  

              The switch to MCR is accomplished by  one  of  two  in-
         structions, depending upon certain SYSGEN conditionals.  For
         MPLUS, this is a BIC instruction, while for M it  is  a  MOV
         instruction.   Both  are  commented  as  "SET  MCR  AS CLI".
         Terminal Driver Modifications                       Page 1-2
         



         Comment out these instructions.

              The driver also resets  the  lower-case  bit,  enabling
         lower-to-upper   case   conversion.   Since  SCLI  is  case-
         sensitive, we wish the terminal  to  be  left  in  lowercase
         mode.   This is accomplished by locating the BIC instruction
         containing "U2.LWC" in the first operand.  Remove the refer-
         ence to "U2.LWC", leaving the other bits intact.  


                                     NOTE

              Several other characteristics are set in this code
              section.   Most  may  be  eliminated, if it is de-
              sired.   Examples  include  U2.CRT,  U2.ESC,   and
              S3.8BC.   It is also possible to alter the default
              buffer size.  The buffer size must be at least 72.
              for SCLI to operate properly.



         1.3  Source Modification

              The desired method of modifying the driver  is  at  the
         source level.  UIC [1,101] contains the MPLUS files; [1,102]
         those for M.  These uics contains the modified TTMOD.MAC, an
         unmodified TTMOD.VGN, and TTMOD.COR.  

              Although M and M+ share the same source module, the up-
         date  versions  are  different, requiring patch sets in both
         [1,101] and [1,102].  The patches may have  to  be  manually
         applied,  and  new correction files built, for later updates
         or releases.   Both  patch  sets  contain  the  audit  trail
         "JMB227".

              The simplest way to apply these patches is to copy  the
         modified  TTMOD  to [11,10] of the sysgen work disk prior to
         SYSGEN.  Since TTDRV is always  re-assembled  and  built  by
         SYSGEN,  this will incorporate the patches.  It is also pos-
         sible to manually assemble TTMOD, and  rebuild  TTDRV  post-
         SYSGEN.   Follow  the  instructions in the release notes for
         rebuilding a driver.  The database doesn't change, so it  is
         possible  to  use  VMR to UNLoad and LOAd the patched driver
         without creating a new system image.  



         Terminal Driver Modifications                       Page 1-3
         



         1.4  Patching TTDRV.TSK

              It is also possible to apply these patches to TTDRV.TSK
         using  ZAP,  or to a running system using OPEN.  In order to
         do this, TTDRV.MAP, plus an assembly listing  of  TTMOD  are
         required.   The  patches add no code, and are thus simple to
         make.  Simply comment out the  "SET  MCR"  instruction  (all
         three  words!),  and  alter the bitmask for the BIC instruc-
         tion.  

              The unmodified  bitmask  is  currently  3047,  and  the
         patched value 3046.  
         
         





                                   CONTENTS



         1.  Terminal Driver Modifications  . . . . . . . . . . . 1-1

             1.1  Overview  . . . . . . . . . . . . . . . . . . . 1-1
             1.2  Modification Details  . . . . . . . . . . . . . 1-1
             1.3  Source Modification . . . . . . . . . . . . . . 1-2
             1.4  Patching TTDRV.TSK  . . . . . . . . . . . . . . 1-3