Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Mon, 16 Feb 2009 17:44:40 -0600

Hi Bernd,

Thanks for this very interesting list.

On Sunday 15 February 2009 14:03:23 Bernd Schoeneburg wrote:
>
> *1. Alarm Distribution over Links (MS or NMS) could be extended by an
> additional "MSI"*
> Often records like calc read data from other records using in-links
> (INPA etc.). The record calculates something that has physically a
> different meaning than the input data. If the input data is not valid,
> the calculation can not deliver a valid result. So MS must be used to
> make this visible. On the other hand, a "high"-alarm in the source
> record should not alter the alarm state of the calc record. Therefore we
> propose to introduce a third choice: MSI = maximize severity invalid. If
> the source record has "invalid" severity, the severity of the local
> record is maximized, otherwise nothing happens.

Great idea, there are spare bits in the pv_link.pvlMask to store this and the 
implementation should be relatively easy.  If this does get implemented it 
will need a corresponding change to VDCT to match (but that's a separate 
task).

> *2. Alarm Disable Field in all Records
> *If a record rises an alarm because of a "known bug" or in case of
> maintenance or special operating conditions, it would be a very smart
> solution to disable this alarm at the source. Otherwise all connected
> clients must mask this alarm individually. Setting all severities to
> "NO_ALARM" does not help if the alarm is set by the device support.
> Setting a new disable-field to "DISABLE" would set SEVR to "NO_ALARM"
> and STAT to something like "ALMDIS" or so. Changing the disable field
> would need some special function which sends out the change. If
> disabled, the alarm bit in the monitor mask is ignored and the
> logAlarms-hook-function returns without doing anything. This change is
> useful if using the conventional alarm handler as well as the new AMS
> used by CSS.

This idea needs some discussion.  There is a related suggestion in my list 
called "OFFLINE Alarm Status" which takes a different approach, requiring 
device support to set an Invalid/Offline alarm instead.  I don't know whether 
using a NO_ALARM severity with a different status would work properly with 
alarm acknowledgments.

> *3. Alarm Delay Field in all Records*
> Beside the alarm limits we have a "HYST" in the analog records. Why not
> also a "DLY" (delay). Some values are very unstable and have some noise
> or over-swing. So a short time over/under the limit should be allowed
> sometimes. Implementing this in the ioc has two advantages: 1.:It is
> analog to "HYST" which is a value-related hysteresis. "DLY" is a
> time-related hysteresis. 2.:Sending a lot of good/no-good messages to
> the clients could be avoided. This change is not so easy, many things
> must be considered.

Any new fields needed can be added to each record type as they are added to 
the support code; they should not be added to dbCommon.dbd though.  I would 
like to see a clear description of how the final alarm code will work, but I 
have no particular objections to these ideas being implemented in the Base 
record types.

> *4. Device Status Field in all Records*
> If the device support encounters a problem, it has only limited
> possibilities to say that to the operators. Alarms could be rised like
> "READ" or "COMM". Detailed information can only be sent to a log-file. A
> string-type field like "DSTA" would be a destination for such messages,
> that could be displayed by each graphic display.

We support writing to a central logServer for this kind of information.  I 
agree that it's not as convenient as putting it in a field, but 40 characters 
for an error message really isn't very many, and adding 40 bytes to the size 
of every record would be impossible for some smaller embedded IOCs.

> *5. get_alarm_double should not return unused limits
> *This has to be explained: When a display widget is coming up, it may
> need some values from the record, like display limits, control limits
> and alarm limits. Alarm limits are needed on a bargraph widget to mark
> some positions with arows or lines. If the corresponding alarm is not
> used, it's severity is set to "NO_ALARM". This means, crossing this
> limit does nothing! Specially when the EGU-range includes zero (EGUL <
> 0, EGUF > 0) then the arrows are missleading.
> The solution: If the alarm is not used, the records function
> "get_alarm_double" should return "NaN" for this limit. In this way the
> client knows, not to display the limit.
> The direct access to the limit fields is not affected.

I agree the current requests for compound types that return alarm information 
are of little practical use to a display widget because they don't account 
for the severity that applies to each alarm level.  However I'd like to know 
what should be returned if I set HSV to INVALID_ALARM, or if I set both HSV 
and HHSV to MINOR_ALARM?  Also the use of NaN values doesn't solve what 
should happen with the DBR_GR_LONG and analogous CA types that have integer 
warning levels — get_alarm_double() requests the values from the record as 
doubles, but dbAccess subsequently converts them to integers if necessary.

> *6. CA Support for "Our ArchiveRecord" and Others*
> The DESY archive record samples "value, time and severity" into an array
> of structures. Unfortunately we can not pass this array over channel
> access directly (as far as I know). So we have additional arrays with
> value (double), seconds_epoch (ulong), nanoseconds (ulong) and severity
> (short). It would be better and more safe (locking is not provided well
> now) if we could use something like an array of
> "DBR_TIME_DOUBLE_STAT_SEVR (or so).

I will leave Jeff Hill to comment on the feasibility of adding new request 
types like this and the idea below to CA.

> *7. CA Request Type for Archiver which includes Deadband (ADEL)*
> The channel archiver can not archive the current ADEL of a PV. So the
> "quality" of an archived value is not known. Between two
> time-value-pairs it is not defined in which corridor the value could
> have been in between. For display and for data compression this deadband
> value is helpful. A new CA request type including the deadband would
> solve the probem.

You could always archive the ADEL field separately, although admittedly that 
would make it harder for the automated tools to use the information.  However 
it doesn't make sense to ask for the deadband for a bi record, which shows 
that this requirement doesn't really make sense for all record types.

> *8. Meta-Info for the Waveform Record
> *The waveform record is often used to hold a buffer contents of a fast
> ADC. The index of the record corresponds to an amount of time, the
> sample time. The value is either an integer, which must be converted or
> a float, which means some engineering unit. We would like to propose
> fields for the sampling rate and/or time scale and the trigger position
> (pre/post) in seconds or in samples. A kind of LINR would also be
> usefull if the array-type is not floating-point.
> These changes would enable the archive viewer to show the events in a
> correct time scale.

Bob already has "CA support for Array with Timebase" on the To-Do list, this 
is similar, probably a superset of what he's asking for.

> *9. Epics General Time: Allow more than one NTP Server*
> It can be, that this is not related to Epics-base. epicsGeneralTime
> facility is using os-depending services. I think osdNTPGet is the place
> were an extension would be necessary, if alternative NTP servers are
> needed. But nevertheless I mention it here. If the desired server (or
> the network path to it) fails, a second server would be better. In my
> changes I once did for the tsDrv in 3.13.x a list of servers in the
> environment variable was foreseen. Perhaps this is possible too now.

General time allows you to register your own time providers, so it should be 
quite easy to add providers for additional NTP servers.  The osiNTPTime.c 
provider in libCom can't talk to multiple servers at the moment because the 
NTP client code in RTEMS wasn't written with that in mind, but we'd be happy 
to see a better NTP time provider if someone wants to write one (preferably 
one with a built-in PLL for doing slow adjustments).  This doesn't have to be 
part of Base, although eventually it could be incorporated into Base.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harold Welte

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System