Re: EPICS alarming on VAL != X

["Johnson, Andrew N." <anj@aps.anl.gov>]

Hi Jamie,

> It seems, though, that this case could be easily covered if either the
> HIGH or LOW alarm were changed to strictly greater/less than the alarm
> value.  Can you think of some reason this behavior would not be desired?

Unfortunately the reason is a common one — because there are probably tens if not hundreds of thousands of IOC databases already in use in control systems at labs around the world, and we have no way of knowing which ones would break if we were to change the existing behavior, which has been in place for 20 years or more.

Changing the behavior of the standard record types is not something we like to do because it means that every existing IOC database has to be looked at closely when it is upgraded to the release of Base that has that modification. As a result any changes we make to the Base record types usually implements the original behavior unless you set some field to enable the new feature.

The current large users of EPICS (APS, SLAC, KEK, Diamond etc.) don't have the engineering staff to rework their existing IOC databases whenever they upgrade Base versions, so we maintain backwards compatibility in new releases as much as we can to reduce their workload. If we didn't do that they might have to freeze the EPICS version(s) they use, which would have effects on maintenance effort needed etc.

In your case if you don't want to manually implement this alarm behavior with calc records you can create your own record type(s) that implements the behavior that you need, starting from whichever Base record(s) most closely do what you're looking for.

HTH,

- Andrew

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