Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 26 Nov 2013 17:57:43 -0600

Hi,

On 11/26/2013 05:20 PM, Evgeniy wrote:

I can easily set scan period to 0.01 second by adding:

choice(menuScan_01_second,".01 second")

in dbd file.

Note that if the IOC's processing of all the records that have SCAN=.01

second takes longer than 0.01 second to execute, the scan rate will drop

to 10Hz automatically. The code in base/src/db/dbScan.c enforces this

(3.14.12.4 will not be as strict, but does still limit the processing

rate if it takes longer than the scan period to process all the records

on the scan list).

What about adding scan period 0.0001 second?
Similar line:

choice(menuScan_0001_second,".0001 second")

doesn't work.

I'm not surprised; what happens? My guess would be that you get about

10Hz, because the record processing takes longer than 100µs to complete.

CLOCKS_PER_SECOND on my 8-core DELL server is 1000000 (running SL5.4).

What should I do to set scan period to 0.0001 second?

I don't recommend even trying to get a periodic scan thread running at

that kind of rate, try to find a different solution to your problem.

There are other ways to trigger a record to process, the simplest is to

arrange for some code to call post_event(n) which will make all records

that have SCAN=Event and EVNT=n be processed once. However this trigger

still goes through a circular buffer which will limit the number of

times you can queue the event to less than 2000.

I need such short period to quickly fill in the circular buffer of
compress record.

You might want to re-think that; the compress record may not be the best

solution to whatever it is you're trying to do -- maybe you could create

your own record type, starting from the compress record source, which

you can initialize manually to whatever state you want it to be in?

- Andrew
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System