9 Apr
2026
9 Apr
'26
5:34 p.m.
Dave,
Since Fortran 77 is not much fun without floating point, you may want to try the RSX
Floating Point Emulator.
Glenn Everhart released this floating point emulator on the Fall 82 RSX SIG tape in
[312,315]. In 1984, my lab acquired a PDP-11/44 but it did not have a FPP. We used this
FPEM software to be able to use Fortran 77 floating point operations. At that time we were
running RSX11M+ V2.1 or maybe V3.0 It continued to be used until at least 1993 or so.
It works by putting a vector to its code which it partially locates in pool to trap
illegal instructions. If the instruction was a FP instruction then it does the work in
software and returns to the user code. It should be FIXed in memory, if it is checkpoint
or moved by a shuffle to a different location after it runs, it will crash RSX. I’d fix it
in memory early in STARTUP.CMD.
I did verify that the FPEM.MAC compiles & links clean on RSX11M+ V4.6, but I didn’t
have an easy way to test it. Below is a bit more info on it that is also in FPEM.DOC
Best Regards,
Mark Matlock
FPEM.MAC- The famous Floating Point Emulator for RSX11M.
I have added support for RSX11M+ in this version and also added some logic for
RSX11M V4 to let it work with headers in new locat- ions. The test site has
not told me how it works in M+ as yet though I believe it will work correctly.
This version needs no system generation (the exec must NOT think there's any
floating point). See the initial part of the source for assembly conditionals
to set for M+ or RSX V4 operation. Assemble and build as any /PR:5 task and
link with RSX11M.STB and run in its own partition (or noncheckpointable, non-
shuffleable in GEN). If it shuffles, the system crashes! To use with F4P or
F77 include F4PEIS in your OTS (replace it into your library). This was
developed from the Los Alamos floating point emulator which was a great start
but didn't work. This does. Under RSX11M+ V2 I have not tested this version,
though I hope it will work. Under M V4 it will work. Note however that it
grabs and does not return some pool when run, so only fix it, and run it in
your system's startup.cmd file. Unstopping it will get it to replace the
system's vectors and exit.
Assembly:
MAC FPEM=LB:[1,1]EXEMC.MLB/ML,LB:[200,200]RSXMC,DU1:[312,315]FPEM
TASK BUILD:
TKB FPEM/-FP/-CP/PR=FPEM,LB:[1,54]RSX11M.STB

On Apr 9, 2026, at 9:32 AM, Dave McGuire
<mcguire(a)neurotica.com> wrote:
Reading it now. Thanks!
-Dave
On 4/9/26 10:31, Johnny Billquist wrote:
OTS manual, chapter 12.
Johnny
On 09/04/2026 16.29, Dave McGuire wrote:
--
Dave McGuire, AK4HZ
New Kensington, PA
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Damn, I was unaware of that. Hitting the docs now. Thank you Johnny.
-Dave
On 4/9/26 09:32, Johnny Billquist wrote:
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To unsubscribe send an email to hecnet-leave(a)lists.dfupdate.se Don't matter if any FP instructions are in
the code or not. A couple of setup instructions are in the RTS initialization, unless you
link with a version of the F77 library intended for code without FP.
The information on how to create a library that don't use FP is in the F77
manuals...
Johnny
On 09/04/2026 15.24, Dave McGuire wrote:
>
> /me slaps forehead
>
> The 11/70's FP board set is flaky, and it has been removed pending repair. I
had forgotten about that. But the "hello world"program shouldn't use any FP
instructions..?
>
> I don't think I can get over to LSSM today, but I will be working there
tomorrow.
>
> -Dave
>
> On 4/8/26 19:59, Johnny Billquist wrote:
>> Error 2, by the way is usually for one of three reasons:
>>
>> 1. Task failed at the SVTK$S call (not able to install trap catching for various
traps)
>> 2. Task uses FP instructions, but task was build without /FP, or system lacks FP
hardware support.
>> 3. FCS initialization failure.
>>
>>
>> Most likely problem would be #2.
>>
>> Johnny
>>
>> On 2026-04-08 22:23, Dave McGuire wrote:
>>>
>>> Hey folks, before I start digging into this, I figuredI'd ask here. A
simple "hello world" program in F77 on RSX-11M-PLUS fails to start thusly:
>>>
>>> $ run hello
>>> TT3 -- Exiting due to ERROR 2
>>> Task initialization failure
>>>
>>> I was trying to move a larger FORTRAN program to this system (the 11/70 at
LSSM) and it was dying with this message, so I wrote a quickie test case to narrow it
down. It's just a write to unit 5:
>>>
>>> WRITE(5,10)
>>> 10 FORMAT(' Hello World!')
>>> END
>>>
>>> ...compiled with "FORTRAN HELLO", and linked with:
>>>
>>> L HELLO,LB:[1,1]F77FCS/LIB
>>>
>>> No warnings or errors. It runs fine on my 11/83 athome with a very
similar config. Before I dig in, can anyone quickly point me to what I'm missing?
>>>
>>> Thanks,
>>> -Dave
>>>
>>
>
>
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