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                 Data Interchange Library Beware File


                            January, 1985


                              VERSION 2





  COPYRIGHT (C) DIGITAL EQUIPMENT CORPORATION 1983, 1985.
  ALL RIGHTS RESERVED.
  
  THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY  BE  USED  AND
  COPIED ONLY IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND WITH
  THE INCLUSION OF THE ABOVE COPYRIGHT NOTICE.   THIS  SOFTWARE  OR
  ANY  OTHER  COPIES  THEREOF MAY NOT BE PROVIDED OR OTHERWISE MADE
  AVAILABLE TO ANY OTHER PERSON.  NO TITLE TO AND OWNERSHIP OF  THE
  SOFTWARE IS HEREBY TRANSFERRED.
  
  THE INFORMATION IN THIS SOFTWARE IS  SUBJECT  TO  CHANGE  WITHOUT
  NOTICE  AND  SHOULD  NOT  BE CONSTRUED AS A COMMITMENT BY DIGITAL
  EQUIPMENT CORPORATION.
  
  DIGITAL ASSUMES NO RESPONSIBILITY FOR THE USE OR  RELIABILITY  OF
  ITS SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY DIGITAL.

                                                                Page 2


1.0  INTRODUCTION

This document supplements  the  Data  Interchange  Library  manual  by
pointing out hints and potential problems.

The  file  DIL.DOC  contains   further   supplemental   documentation,
including installation instructions.



2.0  TOPS-20 VERSION REQUIRED

You must be running TOPS-20 version 5.1 (or a  later  version),  which
incorporates several fixes to NSPSRV, in order to use the Task-to-Task
or Remote File Access routines on TOPS-20.  If you have  a  2020,  you
must run TOPS-20 version 4.1 (or a later version).



3.0  USER-ASSIGNABLE PA1050 INTERRUPT CHANNELS ON TOPS-20

There are no user-assignable interrupts in PA1050 left for  the  COBOL
user  on  TOPS-20  if the IP20 routines in TRAFFIC-20, the Remote File
Access routines, and the Task-to-Task routines are loaded in one  user
program, due to a PA1050 restriction.  Note that using user-assignable
interrupts in PA1050 is not supported.



4.0  REMOTE FILE ACCESS ROUTINES WITH FORTRAN-20 VERSION 7

If FORTRAN Version 7 programs using the Remote  File  Access  routines
get   a  stack  overflow  problem,  the  user  should  rebuild  FOROTS
(according to instructions in  the  Fortran  Installation  Guide),  to
increase the runtime stack space.

To use the rebuilt FOROTS, you must have FORLIB.REL and FOROT7.EXE  in
your SYS:  area.



5.0  USING A SHAREABLE OTS ON TOPS-20 AND TOPS-10

5.1  FORTRAN PROGRAMS ON TOPS-20

Normal loading of a Fortran program with DIL will result in  a  TWOSEG
program  with  a  nonshareable FOROTS loaded from FORLIB.  This can be
saved and executed in a shareable fashion.  If you want  to  load  the
DIL  code in the low segment so that the shareable FOROTS can be used,
you must use /SEG:LOW in the LINK command when loading  your  program.
For  more  information  on  the /SEG link switch, see the TOPS-20 Link
Manual.

                                                                Page 3


5.2  FORTRAN PROGRAMS ON TOPS-10

Normal linking of a TOPS-10 program, using the  instructions  provided
in  the  DIL  Manual, will cause the DIL code to always be loaded into
the low segment.  This means that you can  always  use  the  shareable
FOROTS.  For more information, see the DIL Manual.



5.3  COBOL PROGRAMS

COBOL programs will normally produce low-adress data areas (containing
COBOL   and  DIL  writeable  data),  higher-address  pure  code  areas
containing    COBOL    and    DIL    code,    and    the     shareable
COBLIB.REL/COBOTS-V13.EXE  (on  TOPS-20) or C74LIB.REL, C74O12.EXE (on
TOPS-10) which comes in at higher addresses.   This  behavior  can  be
modified  by  the  appropriate switches to the COBOL compiler (see the
TOPS-10/TOPS-20 COBOL Language Reference manual).



6.0  REMOTE FILE ACCESS TO TOPS-10/TOPS-20 FILES

All TOPS-10/TOPS-20 ASCII files  for  remote  file  access  should  be
specified  as  stream  record format with no record attributes or with
carriage-return/linefeed envelope attribute.



7.0  PRINT RECORD ATTRIBUTE FOR VMS FILES

Record attribute PRINT is only valid for record format VFC on the VAX.



8.0  APPEND ACCESS TO REMOTE FILES

TOPS-10 FAL, which is part  of  NFT  Version  1(5),  and  TOPS-20  FAL
Version  2(207)  do not support APPEND file access.  If you attempt to
append to a remote file on a  TOPS-10  or  TOPS-20  system,  you  will
receive the "network operation failed" error.



9.0  VMS JOBS HUNG IN MWAIT STATE

VMS programs using the Task-to-Task routines in particular,  but  also
other VMS programs, may hang in MWAIT state if the BYTLIM quota is not
large enough, a VMS bug which is not yet fixed in VMS version 3.5.  If
a  program hangs in this state, the program should be tried again with
a larger BYTLIM.

                                                                Page 4


SEE ALSO:  "CLOSING LINKS" (below).



10.0  VMS 3.7 FAL PROBLEM

There is a known bug  in  VMS  3.7  FAL  which  causes  problems  with
communication  to  both  TOPS-10  and  TOPS-20.  Included below is the
patch kit which should be used to correct the  problem.   If  you  are
running  VMS V3.7 without this patch, the DIL routines will return the
status DIT-NETOPERFAIL (Network operation failed).

Copy the patch kit into FAL37.PAT and do the following:

        $ @FAL37.PAT                    ; On your 3.7 machine

Listed below is the patch kit:
[BEGIN PATCH KIT]
!
! Run PATCH to fix SYS$SYSTEM:FAL.EXE
!
$ PATCH SYS$SYSTEM:FAL.EXE
!
! ECO 08        JEJ0031A                02-Oct-1984
!               MODULE: FALACTINI
!               Correction to ECO 07 to correct the problem communicating
!               with FTS-20.
!
!
CHECK ECO 1:7
!
! ECO 08
!       The fix for ECO 07.
!
SET ECO 8
DEFINE  ECO008  = 1600          ! FALACTINI

REPLACE/INST ECO008
'       BICL2   #703,(R8)'
EXI
'       BICL2   #706,(R8)'
EXI

UPDATE
EXI
$ EXIT
[END PATCH KIT]

                                                                Page 5


11.0  CLOSING LINKS

When closing task-to-task links, user programs should ALWAYS call  the
DIL  routine  NFCLS  (Tops-10,Tops-20) or DIT$NFCLS (VAX/VMS) for BOTH
ends of the logical link.  If the NFCLS /  DIT$NFCLS  routine  is  not
called by both the host and the remote programs, then the link may not
be properly closed and all of the resources may not be released.  This
might not be a problem if the user program immediately stops executing
after closing a link, however in programs that continuously  open  and
close  numerous  links,  if the links are not properly closed with the
NFCLS / DIT$NFCLS routine then the user might run out of resources  or
exceed quotas, or on the VAX, get hung in an MWAIT state.

The task-to-task examples in the DIL  manual  are  misleading  because
they  do  NOT contain NFCLS / DIT$NFCLS routine calls for both ends of
the links, although they SHOULD.

[End of DIL.BWR]