May 7, 2001
J. D. Monnier

Star Tracker Shutters Control
=============================

   After Marc put together a cable, we tested your cbtest program with
the modules and it works great.

   I have chosen one particular implementation of shutter control and
have already implemented and tested it in the current version of the
StarTracker.  I describe it now:

   Just as you have written a background task (cb_vxworks) which
monitors the cbcom shared memory to make sure the shutter states
reflect the requested (shmem) states as prepared by the cbcom object,
I have created a background task which runs on cpu 1 with the
startracker which monitors the startracker shared memory
(st_data->blocked[3]).  When blocked[3] doesn't match the
corresponding shutter bit (as defined in shutters.h and cbcom.h and
determined using cbcom_t.Chk_Bit()), a request for a
cbcom_t.Set_Bit(bit,value) is spawned.

  I have tested this by changing the value of the shmem using the Sun
shmem shell and it works great (except for the somewhat flakey
shutters).

e.g.,

   shell> star_tracker -a_blocked 1
   shell> star_tracker -c_blocked 0

ps. Does cbcom_t.Chk_Bit() actually talk to the cbcom modules? My
inspection of your code indicates this just checks the cbcom shmem --
(which is what I want).  is this true?  Also -- When I do a Set_Bit,
does the cbcom module automatically do a check against the shared
memory to make sure the serial writing is necessary?  Currently I am
checking this in my code, but it does look like your code does this
internally as well.