SimH IBM1130 GUI appears "fixed"

JAMES FEHLINGER jfehlinger at
Fri May 12 00:02:09 CDT 2017

I've made little more progress in deciphering the operation
of Carl Claunch's "Lunar Landing" program, as featured in one
of his 1130 YouTube videos. (I'm guessing he's the actual author
of the program -- he mentions on one of his blogs that he was
interested in space before he became interested in computers.)

Recent (official) bug fixes to SimH have made it much easier
to input data to the 1130 console when the GUI is active
(you no longer need to type Return first, to unlock the
console keyboard).

I finally realized that responses to the console's
"ENTER ANGLE" and "ENTER VELOCITY" prompts can be
left-justified numbers, as long as they're
followed by a decimal point.  If you make a typing mistake,
it would seem that Backspace, <ctrl>H and <ctrl>U all
do the same thing -- erase the entire field.  The characters
already typed don't disappear, the cursor just goes to
the beginning of the next line.

The data switches mentioned in the introductory console message are
switch positions (on the GUI) counting (starting with 0) from the left,
not binary numbers.

"4 = SKIP TO PLOT OPTION" means "flip up switch #4" -- not,
in SimH terms, "deposit ces 4" which would turn on switch #13.
If switch #4 is turned on, "examine ces" gives (hex) 800.

The switches apparently really do what they're indicated as doing
in the introductory console message.  E.g., if you turn on
switch #1 (TRACE EVERY TENTH ITERATION), then columns of
numbers will appear on the lineprinter underneath
the headings HOUR MIN 'X' COORD. 'Y' COORD. etc.
These seem to show the progress of the flight, about every
(virtual) 18 minutes.

The ANGLE and VELOCITY values prompted for appear to be **initial
conditions** of a flight, so the reappearance of these
prompts on the console means that your trip has ended
and a new one is beginning (unless switch #6 is turned on,
in which case the program exits when the current flight
terminates).  This only slowly dawned on me -- at first I figured
the re-entered values were a means of steering the spaceship,
or something.

Fine-tuning a flight is apparently done by turning on switch #2
turned on, you get a new prompt on the console, something like

VELOCITY IS      27485. MPH, DIST. TO EARTH,      4058. MILES, AND      239034. MILES TO THE MOON

and you type in something like, I don't know,
and the prompt is repeated with the new velocity and
recomputed distances.  And again, and so forth.

You only seem to get a graphical plot of your trajectory when the
flight has terminated.  Then you see PLOT DIAGRAM IS READY.
and the 1130 goes into a wait state.  When you continue from there,
you get the ENTER ANGLE prompt, etc.

The trajectory plot for a given flight doesn't seem to
appear on the lineprinter until the **succeeding** flight has
terminated.  The visible trajectory plot always seems to be one
flight behind the one just terminated.  I don't know what
that's about.

Also, the angle measurement described in the console instructions --
AND THE MOON" -- doesn't seem to match my trial and error.
If I give an angle of 0. and a very large value velocity (say, 100000.)
then the trajectory plot goes vertically straight up the page,
perpendicular to the line between the earth and the moon.
If I enter an angle of -90. and a similarly high speed, then
the trajectory goes straight toward the moon.  So I don't know
if the instruction message is 90 degrees off or if I'm missing something.
At least the "counterclockwise" part seems to be right.

I don't yet know what causes a flight to terminate, well before
it gets anywhere near the moon.  Maybe the idea is to try to get
a hole-in-one by picking perfect initial conditions.  Maybe the
flight automatically terminates when the ship is so off course that
the program decides the flight has failed.

I don't know what's supposed to happen if you actually manage
to get near the moon -- whether there's some sort of braking and
landing procedure in the program.

I am able to run the program using the DMS disk from
bitsavers configured for 32kw of memory, the 2501 card reader,
and the 1403 printer.  (I had to use the "viewdeck"
utility from and some other things, like Cygwin 'dd',
to split up the original binary deck into two human-readable
pieces and one other component [the "ORBIT" subroutine]
that has to stay binary.  The main program can be made
human-readable, and that's where the Fortran logical unit
number for the printer is defined, and can be changed.)

I may finally give up and attempt to contact Claunch for hints about
how to use his (I presume it's his) program.  But I'm reluctant
to do so, partly because it's fun to try to figure it out myself,
and partly because I don't want to bother or embarrass him.
I know he's posted here in the past, though, so he may see
this anyway.

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