Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 28 Sep 2010 17:45:17 -0500

What do people think of the idea of increasing the size of the CALC field 
beyond 40 characters for R3.14.12?  When replying to this question, please 
bear in mind that:
1. For every additional character allowed in the expression, we have to
   allocate space for up to ~5 more in the tokenized RPCL field
2. Most expressions are short, so most of the extra space will be wasted
3. We still have sites running IOCs on memory-limited micro-controllers

For those that don't know the technology, the CALC string is parsed and 
compiled at record initialization time or whenever you modify the CALC field 
into a string of reverse-polish binary tokens that can be executed very 
efficiently.  A subroutine record would execute the expression faster, but is 
not as flexible since you have to recompile and reboot the IOC to change the 
expression, and that can only be done by someone who knows C and has write 
access to the IOC's source tree.

- Andrew
-- 
If a man is offered a fact which goes against his instincts, he will
scrutinize it closely, and unless the evidence is overwhelming, he will
refuse to believe it.  If, on the other hand, he is offered something
which affords a reason for acting in accordance to his instincts, he
will accept it even on the slightest evidence.  -- Bertrand Russell

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System