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This file describes the files used in the "new" Pascal-20, i.e. the
version that does not depend upon the Pascal-10 compiler and runtimes.
Note that the compiler source files (pascmp.pas, as well as the
temporary passcn.mac and paslnk.mac) are still more or less the same
as the corresponding files for Pascal-10.  This will be kept that way
as much as possible.

There are now versions of Pascal for all combinations of the 
operating systems Tops-20, Tops-10, and Tenex, and the hardware 
KL-10, KI-10, and KA-10.  (The Tenex versions have a few minor 
features missing.) This file describes the Tops-20 version.  If you 
are a Tenex site, this file is also applicable to you, but you should 
also have received a small save set containing binaries for Tenex and 
a file TENEX.OPR explaining a few oddities of the Tenex 
implementation.  The sources for Tenex are the same as for Tops-20.  
If you are a Tops-10 site, you should have received a completely 
different distribution from this one.

Although the compiler itself runs in native mode, it uses SCN7B (the
standard Tops-10 command scanner) to scan the command line.  This will
be replaced when DEC comes up with a standard for Tops-20 compilers.
Until then, the EXEC expects to be communicating with a Tops-10
compiler, so we use the Tops-10 scanner.  SCN7B uses the emulator,
but a RESET JSYS is done to clear emulation mode before the compiler
itself is started.  Note that the command scanner is precisely the
same as that used by Fortran-10, so the EXEC should be modified to
pass commands as it does for Fortran-10.  (In particular, LINK
should be called by /RUN:LINK, rather than LINK!)  If you do not
choose to have Pascal interface with the EXEC, there is a completely
native mode command scanner that will rescan the command line and
supply most of the facilities of the EXEC.  See below.

Note that the memory structure of Pascal-10 and Pascal-20 programs
is slightly different.  The two compilers are as compatible as
possible at the source code level, but the .rel files should be
used only on the machine for which they were compiled, and they should
be loaded with the proper runtimes.  A Tops-10 core image (.EXE file)
can be executed on Tops-20 under the emulator, if it was produced by
edit 74 or later of the Tops-10 compiler.  This export does not
usually include the Tops-10 compiler.

Should you wish to produce a compiler that compiles code to run on
Tops-10, you should edit pasprm.pas to set the appropriate switches
and then recompile.  To produce a compiler that compiles code for
Tops-20 and runs on the 10, you must start with the Tops-10 compiler
and runtimes and recompile them on a PDP-10 with modified pasprm.pas.
I.e. the compilers can each compile code for either machine, if the
appropriate switches are set in pasprm.pas.

The distributed version assumes that the Pascal runtime library is
sys:paslib.rel.  This can be changed by editing pasprm.pas and
recompiling, or by clever use of Filddt.  (The strings "SYS  " and
"PASLIB    " are stored in Ascii in the compiler.)



***********compiler***********


Compiler source files.  (.rel files may or may not appear in your
distribution.)

pascmp.pas - main compiler source.  (identical to the tops-10
		source, except that the extended lookup arguments
		have been commented out in reset and rewrites in
		the startup code.)
pasprm.pas - parameter file "required" by pascmp.  Sets up operating
		system and site dependent options.  If this is changed
		you must recompile pascmp.pas and then reload.
paslnk.mac - low-level compiler routines
passcn.mac - compiler link to SCN7B, which is currently used to scan
		the command line.  Note that paslnk and passcn are
		temporary modules, until DEC allows us to supply a
		real Tops-20 command scanner.

The compilation process assumes that you have the following .unv files: 
	Pascal-20:  pasunv.unv
	Tops-10 (until paslnk and passcn are replaced): c.unv,
		scnmac.unv
	Tops-20	(normally on sys: at all Tops-20 sites): monsym.unv

The loading process assumes that you have the following standard
Tops-10 modules (also part of the temporary command scanner):
helper.rel, scn7b.rel

These auxilliary files are all included in the distribution, except
for monsym.unv, which we assume you have.

A file pascal.ccl is included.  It is an indirect command file for
LINK to load the compiler.  To create a new compiler, compile
PASCMP.PAS with the current pascal, and then do
  @LINK
  *@PASCMP
  */G
  @SAVE PASCAL
If PASLIB is not on SYS: yet, you will also have to do
  *PASLIB/SEA
No D command is needed at the moment.

If you don't want to recompile the compiler, all you really need
is the thing itself, which is

pascal.exe - Pascal-20 compiler

********compiler for those not adding PASCAL to the EXEC********

For those who do not want to add PASCAL as a known language, there is
an alternate command scanner that does not require the use of the 
EXEC.  The files are:

paslnx.pas  -  the scanner itself, sort of equivalent to passcn.mac
paslny.mac  -  a few MACRO support routines, sort of equivalent to
		paslnk.mac
pas.ccl - an indirect file to LINK to load this.  I recommend saving
		it as PAS.EXE, to save typing.  This command file
		also assumes that PASLIB.REL is on SYS:.  If not
		you will have to mention PASLIB/SEA to LINK.

Two other general packages are used by paslnx.pas.  The .MAC files are
the source for the package, the .PAS files are designed to be INCLUDE'd.
  pascmd.mac,pascmd.pas  - a general-purpose comnd jsys interface
  string.mac,string.pas  - the (unimpressive) beginning of a set of
	runtimes to do string manipulations on packed array of char.
	This uses ADJBP, so Tenex people would have to convert them.
	They are not used in the Tenex version at this time.

The same compiler source and .REL file is used:  only the command
scanner is changed.  If you say PAS<cr>, you will get a native-mode
scanner with the same switches as documented in the manual.  However
instead of REL,LST=SOURCE, it will want just a source file name.  It
will produce a .REL file by default.  You can suppress the .REL file
by /NOBIN, and cause a listing file to be created by any listing
switch (/LIST, /CREF, or /OBJECTLIST).  The scanner rescans the
command line, and in this mode simulates the EXEC's EXECUTE and DEBUG
commands.
   PAS TEST    		is equivalent to EXEC TEST.PAS
   PAS TEST/DEBUG	is equivalent to DEBUG TEST.PAS
   PAS TEST/LOAD	is equivalent to LOAD TEST.PAS
   PAS TEST/NOLOAD	is equivalent to COMPILE TEST.PAS
The same conventions about not recompiling if there is already a .REL
file, etc. are followed.  /COMPILE forces compilation even if the
dates don't compare.  All normal compiler switches are also allowed.
The .REL and .LST files, if any, use the same name as the source file
(truncated to 6 characters if necessary), on the connected directory.

Note that there is a possible confusion about /DEBUG and /NODEBUG.  In
the normal compiler, we have two orthogonal decisons:
   debug code compiled?  YES	/DEBUG	(default)
			 NO	/NODEBUG

   debugger actually used? YES   EXEC DEBUG command
   			   NO    EXEC EXECUTE command

In this version, since the EXEC is not involved, it is all done with the
/DEBUG and /NODEBUG switches:

				debugger actually used?
			      YES			NO

   debug code   YES	/DEBUG			default	
   compiled?	NO	impossible		/NODEBUG


*******EXEC linkage********

exec.pat - instructions on how to patch the EXEC to link to PASCALL.  
		This file assumes that you do not have sources, and
		thus tells you how to make the patch in FILDDT.  It
		does not assume very much knowlege of DDT, at least
		to do the easiest version of the options.
exec.ddt - the EXEC patches themselves.  See exec.pat first.

The files EXEC.PAT and EXEC.DDT depend upon which release of the EXEC
you are using.  Here are the currently available versions of the files:

  release       EXEC.PAT         EXEC.DDT

  3 and 3A	EXEC3.PAT	FILDDT.DDT
  4		EXEC4.PAT	EXEC4.DDT

*******runtimes********

The runtime sources are the following.  (Note that pasunv.mac compiles
into pasunv.unv, which is also needed by the compiler sources.)

pasunv.mac - symbols used by all runtimes
pasio.mac  - I/O runtimes (modules pasio and danger)
pasnum.mac - I/O conversion routines
passtr.mac - I/O to/from strings
pasddt.mac - low-level routines for pasddt (module debsup)
pascnv.mac - misc. sixbit conversion, etc.
pasdat.mac - date/time routines (replaces routines from the Fortran
		library used in the 10 version, since they use UUO's,
		and we can't tolerate having the emulator called)
paspsi.mac - interrupt handling routines
heap.mac   - new and dispose used when DISPOSE is called
debug.pas  - pasddt

There things are all put together with maklib to form a library, which
you should certainly take (and just replace single modules when you
recompile).  However pasddt.rel should not be linked into the library.
Instead it should be put on sys: as pasddt.rel.  Loading it will
cause things to be set up so that you get a debug.  (Otherwise there is
no way to control when pasddt gets loaded.) 

Should you not wish to recompile, simply put the following on sys:

paslib.rel - runtime library for Pascal-20
pasddt.rel - pasddt

extern.pas should be put somewhere where users can read it.  It
contains declarations for external procedures not built into the
compiler (as described in the manual).

*******Details for numerical hackers**********

There is a problem with programs that use Fortran subroutines:
If an error occurs, Fortran will call its error processor, which
will print an error message using TTCALL's.  This will invoke
the emulator, and the next time Pascal tries to expand core, the
emulator will stomp on your program (ill mem ref).  I have no
good solution at the moment.  However I am including a copy of
FORDUM.MAC, the fortran error processor, which has been
"nativized", i.e. made native mode.  You can load this explicitly
as part of your core image, put it in FORLIB instead of the
version DEC supplies (using MAKLIB), or add the code to
PASIO.MAC so it is always loaded.  The advantages of the various
methods are:
  adding it to PASIO.MAC - it is there when you need it, and you
	do not have to change FORLIB
  putting it in FORLIB - you do not get it for programs that
	don't use Fortran subroutines.  Note that FORLIB is
	constructed in such a way that FORDUM is not loaded with
	real Fortran programs.  It is strictly a dummy module for
	use when Fortran routines such as SIN and COS are called
	by other languages, as in this case.  Since other languages
	(e.g. SAIL) have the same problem with the emulator, it
	seems reasonable to always use the nativized Fordum.  
	It should act precisely the same as DEC's, but just not
	invoke the emulator.  So we strongly recommend replacing
	DEC's version of FORDUM with ours in FORLIB, until they
	make Fortran be native mode.  At that time the problem
	should go away.
		maklib
		forlib=forlib/master:fordum,fordum/replace:fordum
  loading it explicitly - you do not get it for programs that
	don't use Fortran subroutines, and you do not have to
	change FORLIB
As far as I can tell, this FORDUM should act exactly the same
as DEC's, and would even work with real Fortran programs.  However
it has not been tested very much.  I recommend putting it in
FORLIB.

We have had some requests for more friendly handling of 
arithmetic errors (e.g. divide by zero, floating underflow).  At
the moment we print an error message and bomb the program.  I
still believe that is the correct thing to do unless the user
specifically has designed his program to take errors into account.
However for those having special need, I have included two files
with procedures designed to be set up as interrupt handlers for
arithmetic exceptions.  ZEROVR.MAC simply zeros the result and
goes on.  CALFOR.MAC actually invokes the Fortran arithmetic
exception handler.  See the extensive comments at the beginning
of ZEROVR.MAC for a discussion of the issues involved in
handling arithmetic error.  In those comments a 5 line macro
program is given to allow you to test explicitly whether an error
has happened from the Pascal program, and have the program
recover for itself.  I strongly recommend that style of operation,
rather than setting up interrupts.

NB:  CALFOR and ZEROVR currently use KL instructions (DMOVEx, ADJSP,
	and ADJBP), so they should be converted if anyone on Tenex
	wants them.  This is a very easy job, but one that I don't
	have time for at the moment.

*******Random packages*******

These things will probably be put in PASLIB when they have been
tested.  They use KL op codes, but they are only relevant for
Tops-20 anyway, so this should cause trouble for Tenex people.
   PASCMD.MAC, PASCMD.PAS - complete support for the COMND jsys.
	PASCMD.PAS has the declarations in it, and is designed
	to be INCLUDE'd.  It also has the documentation as comments.
   PASPTY.MAC - two routines for openning PTY's.  Includes
	documentation.  Just helps you get and open PTY's.  You
	still have to do your own timing.

FORTIO.MAC contains routines to allow you to call fortran
subroutines that do Fortran I/O.  It should be self-explanatory.
It has not gotten much testing, but the current state will at
least provide some advice to system programmers who have to do
this in a serious way.  When DEC comes out with native-mode
Fortran, the interface will probably change.  The code that will
most likely change is under a conditional, KLUDGE.  Also, it is
possible that something will have to be done about JSP RESET.+1
The idea is that we need all of that routine except the RESET
UUO itself, which is the first instruction.  If the 20 version
begins with a RESET jsys, then RESET.+1 will still be the right
entry point.  If not, some better mechanism may be needed.

PFORM.PAS is a formatter.  It is offered as an alternative to
CROSS.  The other purpose of cross was to produce a crossreference
listing.  I believe the the /CREF switch, together with DEC's
CREF program, do a better job of this.  This formatter is
from Stanford.  I have not tested it significantly, and make
not guarantees about it.  When compiling it, you must have
P: defined as a logical device pointing to some directory on
which the file PASCMD.PAS is resident.  You should load this with
PFORMS.MAC, which contains some system-dependent subroutines.
Currently PFORM is supported on Tenex only if you have PA2050.

PASSRT.MAC is an interface to DEC's SORT/MERGE.  Version 4 of
SORT is required.  Docmentation is at the beginning of PASSRT.MAC.

*******Documentation********

The manual is produced using an old version of Brian Reid's SCRIBE 
system.  This allows automatic production of crossreferences, tables 
of contents, etc. The files involved are the following:

pascal.mss - the "manuscript" file (i.e. the main source file)
pascal.aux - table of crossreferences (produced by the previous
		run of Scribe - should always be kept around for
		use by future compilations)
pascal.doc - the final manual

As I mentioned above, the version of SCRIBE we used for this manual 
is an old one, produced before Brian became as serious about it as he 
is now.  He has now made it into a serious product, and it is being 
marketed by Unilogic, Inc. The version included here is far out of 
date compared to what is currently being distributed, and includes 
only the one document type and device type needed to make this 
manual.  If you like what you see, we encourage you to get the real 
thing from Unilogic:
  Unilogic, Inc.
  605 Devonshire St.
  Pittsburgh, Pa. 15213
In addition to the program, documentation, reference cards, and a 
collection of other document types are available.

The files included in this distribution are:

scribe.exe - The scribe program.  Assumes the data base is on DSK:.
		You would normally have a <scribe> directory, but this
		one is set up for dsk:.  (It can be changed by
		depositing 1,,1 in location 140 and starting scribe.)
file.dev - definitions for the "device" file, i.e. for producing .DOC
		files.
crt.tfo - characteristics of the character set assumed available.

An alternate manual is also included.  It does not describe all of
the more abstruse features, but should be much easier to understand.
It is designed to be compiled with the current version of Scribe,
though the version included here can probably be used with some
small amount of work.  The files are
   PASCAL-MEM.MSS - source
   PASCAL-MEM.DOC - the document
It is intended that this document should be called PASCAL.MEM when
it is finally put on your system.