On Donnerstag, 19. März 2009, Dirk Zimoch wrote:
> Changing the alarm limits on the fly might confuse some client programs.
> The records will behave correctly (i.e. change their alarm status at the
> new limits), but client programs that display alarm limits (e.g. as
> colored areas on a meter or bar) usually only read the limits when they
> connect for the first time.
Since this question/problem comes up so often, I'll take the opportunity and
hijack this thread to ask why this hasn't been fixed years ago. According
to the spec, CA uses only 3 of 16 available bits for the event mask. So
let's use a few more of those bits for the most commonly needed event
types! Even using only /one/ more bit would be extremely useful, while
retaining complete compatibility at the protocol level:
DBE_CONTROL An attribute of the PV has changed. This includes any
attribute of the DBR_XXX_GR and DBR_XXX_CTRL types
other than thos in DBR_XXX_TIME, i.e. stamp, status,
severity, time, value.
Adding this to CA would pave the way. The next step is in the database
layer, namely at the record support level and in base, where the new bit
mask must be added to the right db_post_events calls. However, this can be
done incrementally, one record at a time. Updating clients can be done,
too, whenever someone has the time and energy available, there is no hurry
and no need to closely synchronize developments.
If I have overlooked some serious drawback in this proposal I'm sure someone
will point it out soon...
Cheers
Ben
- Replies:
- Re: Attribute events; was: Alarm Limits Andrew Johnson
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