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Subject: Re: Fwd: CA link behavior
From: Ralph Lange <[email protected]>
To: Andrew Johnson <[email protected]>
Cc: [email protected]
Date: Thu, 10 Dec 2009 11:28:39 -0500
On Wed 09 Dec 2009 17:18:10 Andrew Johnson wrote:
On Wednesday 09 December 2009 15:06:23 Ralph Lange wrote:
I can see the unexpected string type link behavior possibly being
intended to do something like an auto-save/restore on record C. This
could be an interesting feature, if (and only if) it is independent from
data type (obviously) and configurable (which requires a CA protocol
change to allow the link spec to define target record processing -
instead of the PP option of the target field now used for that purpose).

[...]
I do not plan to make the above change, and in fact I will probably comment out both lines, because in the future I think we should look at adding a flag (ROR = Resend On Reconnect?) to output links to allow users to turn this behavior on. I can see it as being useful in some cases. I'm not so sure about the idea of a put without causing processing though...
Hi Andrew (did you shovel your way into work?),

Real world example:
Consider a setup where record C on ioc2 is a device (e.g. power supply) set point connected to hardware, while B on ioc1 is part of a convenience layer on a soft IOC (e.g. converting field to magnet current) that writes to the device. In addition to B, C is also being shown in detail panels and being archived, so rebooting ioc2 should be bumpless. The general guide line would be: After a reboot the system should be as close to the prior state as possible, but without any additional record processing. To meet that goal, even though B.OUT should normally process C when fired, after a reboot of ioc2 it should only put the value, without processing C. On the other hand, as the workaround is simple and reliable (put C in auto-save/restore pass 1), I'm not sure how much effort can be justified.

Hm... I would really like the link spec being able to specify processing the target on OUT links, too (instead of using the target field's PP flag), so that the CA related flag set would become:

CA  Force link to use CA
CP  Force CA, process receiving record (both INP and OUT links)
CPP Same, but only if receiving record is passive (INP and OUT)
SOR Send on reconnect
POR Process on reconnect (only passive if CPP is true)

Actually, things could then even be made more orthogonal:

<none>/CA            Auto link                [default]
                    / Force CA link
<none>/P/PP          No processing            [default]
                    / Process receiver
                    / Process receiver if Passive
<none>/SOR/POR/PPR   No reconnect action      [default]
                    / Only send on reconnect
                    / Send and process receiver on reconnect
                    / Send and process rec. on reconnect if Passive

For completeness, DB could be added for the first set to force local resolution (I don't see a use case, though).
The second set would be valid for DB and CA links.
The third set would be valid for CA links only.
All sets would be valid for INP and OUT links.

To keep compatibility, on input links .CP would translate to .CA.P and .CPP to .CA.PP (sorry to be obvious).

Ralph


Replies:
Re: Fwd: CA link behavior Andrew Johnson
References:
Re: CA link behavior Andrew Johnson
Re: Fwd: CA link behavior Dirk Zimoch
Re: Fwd: CA link behavior Ralph Lange
Re: Fwd: CA link behavior Andrew Johnson

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