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35511RE: [SeattleRobotics] Re: Forth for Robots (from Loki's first steps)

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  • Randy M. Dumse
    Feb 12, 2008
      Dave Hyland had asked about the compession of code, and I had
      mentioned the LLE project. Larry Forsley, who did it, wrote me
      he was back from vacation, so I asked him about the details. He
      sent an extended, but rather interesting reply. In particular
      the last few paragraphs talk about "hacking" in the sense
      research was done by interactive testing with tweaked constants
      and hand adjustments, yeilded to verification of a patented
      process of upconversion of photons. Dave, this is my basis to
      say on a large project, not only the object produced will be
      smaller, the source often compresses much more than most would
      believe. I had suggested a 5:1 reduction, which people found
      difficult to believe. Larry here documents an actual case ~100:1
      reduction. Hope you enjoy the read, I did.:



      The laser control power conditioning system that I built in the
      late '70s was originally written in Fortran whose source code,
      specification and documentation filled a shelf full of 3 inch 3
      ring binders, probably close to 20 in all, which with tapes and
      backups and things filled a good 6 - 8 foot shelf. The Forth
      code, including the operating system source code fit in one 1
      inch binder and the power conditioning source code was about 10
      pages, or 30 Forth blocks.

      The Fortran system also included a microcoded Hewlett Packard
      21MX minicomputer that ran a relational description language
      (RDL) I had devised prior to finding out about Forth in 1976 or
      so. It was an interpretive system that stored spatial and
      temporal relationships of components, sort of Smalltalk-like
      (which I didn't learn about until the mid-80s). General
      Electric Trident Missile Systems built the system to my and
      another engineer's specifications.

      However, GE signed up to deliver the system in August of 1977,
      thinking that would be fine for meeting our September, 1977 DOE
      milestone. Unfortunately, the milestone required an operating
      laser, not just the power conditioning system.

      One of our EE staff had gone up to Ottawa to a semiconductor
      plant auction and bought two HP2114 computers: replete with 16K
      words of core memory! My first inhouse Forth system went on
      these, and, Ken Hardwick of the mainframe University computing
      center, put a full multi-tasking, multi-user operating system,
      URTH, or University of Rochester Forth on them. Ken had the
      prescient to make the first high level version of ;code, that,
      like Chuck, he also called ;: later to be renamed DOES>.

      I took the system and put a full laser amplifier testbed
      together and with one computer in Rochester and one at Raytheon
      in Massachusetts, we "rang out" all of the laser amplifiers.

      In the early spring of 1977, after I realized that GE wouldn't
      give us the 3 months we needed to run the laser under automated
      control, I commandeered Dan Gardner from GE (who hated Forth)
      and we wrote a complete 6 beam laser power conditioning control
      system. I think we started in April and were done by June.
      That gave June, July and August to test the laser, while waiting
      for the "real" laser control system to come on line. The test
      only needed 4 beams, but the first experimental laser would be
      the 6 beam Zeta, so I figured, what the hell!

      Naturally, the top down build to the specs approach, so
      "apropos" to the military and nuclear submarines, didn't work
      too well with a small University embarked on building the
      world's largest laser for fusion studies. As we wrote the Forth
      code and found out how the laser really worked, bit sense or
      control polarities were wrong, bit assignments were wrong, muxes
      were wrong, etc, we fed that over to the software group so they
      could correct the spec.

      I always liked the idea of an "executable spec": e.g. the
      software.

      At the end of the day, it was decided by Moshe Lubin, the
      director of LLE, that since we'd spent a half million dollars
      and probably 5 man-years building the "real" software, we'd
      better use it. I fought this ridiculousness, but abstained at
      the end.

      Instead, the following systems came up in Forth:

      24 beam laser alignment system, primarily written by my students
      over a couple classes and two programmers, running on an LSI
      11/23 with 256Kbytes of RAM, floppy disk and a 10 MB RL01 hard
      drive, multiple color consoles, 24 tasks, etc. Lawrence
      Livermore ran a 20 beam system on a VAX-780 networked through a
      PDP-11/70 and hundreds of LSI 11/23 computers, each one
      responsible for 4 mirror control systems in the laser. We
      could align and shoot every 30 minutes. Livermore could do the
      same every 2 hours.

      There was probably 2 man-years of effort in LLE Laser control
      system and easily 100+ man years in the Livermore system. I
      discussed this with their engineers one time, and found that
      probably 20% of their effort went into building a sufficiently
      robust RS-232 based communications infrastructure to support the
      communicating tasks, synchronizing them, etc, in the
      pre-Ethernet era.



      Glass Development Laser (GDL, also known as the God Damn Laser)
      power conditioning and safety interlocks for multiple
      laboratories.

      Optical Multichannel Analyzer (OMA) on the back of various
      streak cameras

      The GDL and OMA systems performance and flexibility allowed
      Stephen Craxton, a British theoretical physicist, to verify his
      2 wave mixing theory using "detuned" crystals to get 100%
      conversion of infrared photons to ultraviolet photons (2 red ->
      1 green, 1 red and 1 green -> UV). This saved laser fusion in
      the mid-80's, and gained LLE a significant patent using two
      birefringent crystals each "detuned" about the extraordinary
      axis of rotation. This is the standard method through out the
      world of building high power lasers for fusion and other
      studies, as well as smaller systems for a variety of purposes.

      Bob Boni, Steve Craxton, a GDL operator and occasionally me,
      would run GDL nights when no one else was around to rotate the
      crystal pairs, under Forth control, fire the laser, under Forth
      control, operate the streak camera OMA, under Forth Control, and
      within seconds of a shot know where we were on Steve's plots.
      Then, we'd recycle the laser rotate the crystals or adjust the
      laser power, and fire again. We literally stepped right through
      Steve's curves, nailing them with experimental data.
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