Re: [foxboro] Impact of external references in an IND block
- From: Neil Martin <neil_martin@xxxxxxxxxxxx>
- To: foxboro@xxxxxxxxxxxxx
- Date: Fri, 8 Feb 2013 10:53:08 -0600
Alex,
Is Invensys actively doing something to enable us to type in "
:Block.Parameter " configuration links within IEE? At least with our IEE
V1.2.2, we are not able to do it. We have to type in the
Compound:Block.Parameter even when the blocks are within the same
Compound.
Conroe & Dayton , TX.
Conroe ph) 936-760-6205
Dayton ph) 936-257-4212
pager) 936-522-0052
"Johnson, Alex P (IOM)" <Alex.Johnson@xxxxxxxxxxxx>
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02/08/2013 09:51 AM
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Re: [foxboro] Impact of external references in an IND block
Re: I want to know the impact if any as a result of large number of
external references in an IND block.
There is no definitive answer. However, there are two constraints:
1) The number of external references per second (covered in this question)
2) The impact of multicast messages on your system (covered in the next
question)
External References per Second
An "external reference" is one that mentions a CBP, AOA, or SV directly,
e.g.,
:C.P := 1; # C.P may be in the CP or external to the CP
:C:B.P := 2; # CBP may be in the CP or external to the CP
:MY_SV := 3; # SVs are always external to the CP
:A:O.A := 4; # AOAs are always external to the CP, but you can't tell
a CBP from an AOA by looking at the name
There are two different behaviors for lines like these.
If the externally referenced top level name (C in CBP, SV, or A in AOA) is
outside the CP, the block will suspend for one PERIOD.
If the externally referenced top level name is inside the CP (only
possible with a C:B.P or C.P), the block will NOT suspend, but the
instruction is slower than a simple ADD or SUBTRACT type instruction.
This means that you can issue only one "external reference" to a compound
in a different CP each BPC from a given sequence block.
I once had a client call an yell at me because he had 20 lines of HLBL
code that took 10 seconds to run and he needed it to happen in 0.5s. I had
him send me the code and it was 20 lines of external references trying to
implement a safety shutdown. That won't work in 0.5s. It takes 10 seconds
with a PERIOD of 0.5s.
-----
Re: What is the limit to the number of external references that you can
set using an IND block?
There is no limit other than lines of code, block count, and memory.
However, the CP uses its IMPORT table to eliminate multicasts from
external references. The import table is an OM construct that holds the
address of "top level names" that the CP has previously used.
If the table is full, the CP will revert to multicasts to find the data.
In general, it is a good thing to minimize the number of multicasts so you
want to avoid filling this table.
The IMPORT table in the CP10 holds 50 top level names (Cs, As, or SVs).
All other CPs have space for 100 top level names. If you try to access
more than 100 different top level names from a single CP, you will start
generating multicasts.
-----
Re: What should be the ideal block scan rate if there is a large set to be
written
It's up to you. You can have one outstanding external reference per IND
block per PERIOD.
Regards,
Alex Johnson
Invensys Operations Management
10900 Equity Drive
Houston, TX 77041
+1 713 329 8472 (desk)
+1 713 329 1600 (operator)
+1 713 329 1700 (Central Fax)
alex.johnson@xxxxxxxxxxxx
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