The light beam control (LBC) part of the PDP-11 replacement project
(PDPRP) basically consists of two parts: a C code (pdprp.c) which does the
processing and issues the bench calls to the LBC units and a Tcl/Tk code
(pdprp.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.

Eventually, additional code (both C and Tcl/Tk) will be needed for
telescope position and filter control.  I am not yet sure if I will do
this monolithically by adding on to the existing codes or learn how to
send messages back and forth between concurrently running applications
and generate separate sets of codes for these two aspects of the project
(ex. tel.c and tel.tcl...).

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.