Further clarification on Hall D controls stragegy

[Elliott Wolin <wolin@jlab.org>]

Hall D Electronics:

Hi,

A few thoughts concerning controls strategies in Hall D:

Everything I've written so far should be understood as desires, not requirements.  The 
online will be extremely flexible, and should be able to handle anything reasonable, 
including having to read controls info via VME (of course, we will need to control the 
number of types of hardware and software needed, to keep within our cost and manpower 
budget).

But what is possible may not be desirable.  As we saw in CLAS, it is best not to interfere 
with the high-speed readout on the VME backplane, if possible.  These days cpu's are 
faster, buffers are bigger, etc, so the problems we had in CLAS are not likely to occur. 
But they are guaranteed not to occur if the high-speed DAQ system does not have to share 
VME cycles with a controls system.

How much we are willing to spend (time, money) to separate the two streams?.  Not that 
much, in my opinion, maybe very little.  But after talking with Fernando it seems there 
are a number of simple and inexpensive ways to separate the streams.

At this point I'll leave it up to electronics experts...I've expressed my mild preference.

As for a requirements document, I'm not sure any is needed, as there really is no 
requirement (other than that we cannot read out voluminous controls data via VME in DAQ 
crates, which no one is proposing).

Finally, concerning our monitoring/alarm strategy, I much prefer to monitor as much as 
possible, and alarm appropriately.  It is much easier to debug weird problems if you have 
a complete set of monitoring data, and precursors to incipient failures often show up in 
monitoring data (increased current draw, temperature rise, etc).  The more monitoring 
capability, the better, in my opinion.


				Sincerely,
					Elliott


================================================================================


  Those raised in a morally relative or neutral environment will hold
		    no truths to be self-evident.
				

Elliott Wolin
Staff Physicist, Jefferson Lab
12000 Jefferson Ave
Suite 8 MS 12A1
Newport News, VA 23606
757-269-7365

================================================================================