The light beam control (LBC) part of the PDP-11 replacement project
(PDPRP) basically consists of two parts: a C code (lbc.c) which does the
processing and issues the bench calls to the LBC units and a Tcl/Tk code
(lbc.tcl) which is the graphical interface the observer will interact
with to operate the mirrors.  The C code opens a channel to and starts
the Tcl/Tk GUI.  The Tcl/Tk GUI, in turn, calls routines in the C code
such as start and stop cycling.  The C code also calls routines in the
Tcl/Tk code. Apparently, the C code can only send up to 80 chars via
Tcl_GlobalEval to the Tcl/Tk code.

There is additional code for telescope control (telcon.c & telcon.tcl)
and more is needed for things like filter control etc.  

I have flowcharts for how the basic program structure should (and does
to the most part) work which I will someday make available and/or update
to show the real workings of things. Until then, they can be found in
/home/begonias/sjk/Xfig as *.fig. They are, of course, Xfig drawing files.