Re: [foxboro] FCP vs. ZCP? (forked from: network storm)

  • From: tjvandew@xxxxxxxxx
  • To: foxboro@xxxxxxxxxxxxx
  • Date: Fri, 13 Feb 2009 03:22:39 +0000

That is an excellent explanation.  Thanks Alex!
Sent from my Verizon Wireless BlackBerry
-----Original Message-----
From: "Johnson, Alex P (IPS)" <alex.johnson@xxxxxxxxxxxxxxxx>

Date: Thu, 12 Feb 2009 19:51:38 
To: <foxboro@xxxxxxxxxxxxx>
Subject: Re: [foxboro] FCP vs. ZCP? (forked from: network storm)


Tom,

The UCM was an older controller whose I/O can be attached (migrated) to
a CP270. 


As far as FCM loading is concerned, you can improve overall I/O response
by using more FCMs per ZCP. You can improve if further by ordering the
ECBs for the FCMs properly in the _ECB compound.

When the ZCP wants I/O, it sends messages to the FCMs that hold that I/O
in the order that their ECBs appear in the _ECB compound.

It then calculates how long it should wait for the first FCM to gather
its I/O and then asks for it. If the FCM is finished gathering, the ZCP
gets the data and moves to the next FCM.

If the FCM is busy, the ZCP sits backs and waits a bit more before
asking again. This cycle is repeated as necessary.


Since the FCMs are queried in parallel, the more of them you have the
more parallel processing can be achieved and the less the ZCP has to
wait for its data.

Also, as you might have realized, this means that FCMs with short FBM
chains should be place higher on the list of ECBs in the _ECB compound.
This allows the ZCP to wait a shorter time to get that data. Since the
other FCMs are processing in parallel, it is increasingly likely that
they will be ready if they are listed in increasing chain length.

Does this make some sense?



Regards,
 
Alex Johnson
Invensys Process Systems
10900 Equity Drive
Houston, TX 77041
713 329 8472 (desk)
713 329 1600 (operator)
713 329 1944 (SSC Fax)
713 329 1700 (Central Fax)
alex.johnson@xxxxxxxxxxxxxxxx



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