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<== Date ==> <== Thread ==>

Subject: Re: Default value to field SCAN
From: Andrew Johnson <anj@aps.anl.gov>
To: <tech-talk@aps.anl.gov>
Date: Tue, 3 Jan 2017 12:23:16 -0600
On 01/03/2017 05:57 AM, Gabriel de Souza Fedel wrote:
> When I create records and don't set the field SCAN, what is the default
> value? There is an way to change this?

For DBF_MENU field types the default value is usually the first of the
choice() entries declared in the relevant menu definition loaded by the
IOC. An individual record-type's .dbd file can override that standard
default value for fields that it defines, but not for fields declared in
the dbCommon.dbd file.

The SCAN field is declared in the dbCommon.dbd file, and the relevant
menu is menuScan, the first choice of which is Passive, so that will be
the value of any SCAN field which is not explicitly set during the
record loading or IOC startup process (remember that tools such as
autosave can modify record field values during the iocInit process).

You can build an IOC using a locally modified version of the
menuScan.dbd file (thus you can have different scan rates for each IOC
if you wish to) but you must leave the first three entries (Passive,
Event and I/O Intr) exactly as they are defined in Base, and you must
have at least one periodic scan rate defined. Recent versions of Base
will give a warning during iocInit if any of these conditions are not
met by the menu(menuScan) definition.

> I'm having problems with a set of records without SCAN field that are
> consuming a lot of CPU, and receiving this messages:
> 
> dbScan warning from '.2 second' scan thread:
>         Scan processing averages 0,00 seconds (0,00 .. 0,02).
>         Over-runs have now happened 283681 times in a row.
>         To fix this, move some records to a slower scan rate.
> 
> dbScan warning from '.5 second' scan thread:
>         Scan processing averages 0,00 seconds (0,00 .. 0,03).
>         Over-runs have now happened 290049 times in a row.
>         To fix this, move some records to a slower scan rate.
> 
> dbScan warning from '.1 second' scan thread:
>         Scan processing averages 0,00 seconds (0,00 .. 0,03).
>         Over-runs have now happened 278431 times in a row.
>         To fix this, move some records to a slower scan rate.
> 
> If i remove small choices from dbd file (.1, .2 and .5 seconds) solves
> the problem. Apparently the records are being created with all SCAN
> values...some idea to solve this?

These symptoms are very strange; as Mark Rivers suggested those average
processing times should be larger than the nominal scan period. Please
cd to your base/src/libCom/test directory and type 'make runtests' and
report any test failures here. Also please try running the IOC with the
LANG environment variable set to "C" instead of whatever it is currently
set to in case that is causing the problem.

- Andrew

-- 
Arguing for surveillance because you have nothing to hide is no
different than making the claim, "I don't care about freedom of
speech because I have nothing to say." -- Edward Snowdon

Replies:
Re: Default value to field SCAN Gabriel de Souza Fedel
References:
Default value to field SCAN Gabriel de Souza Fedel

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