Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 24 Jul 2014 11:27:24 -0500

On 07/24/2014 04:47 AM, Benjamin Franksen wrote:
> On Thursday 24 July 2014 11:15:56 Dirk Zimoch wrote:
>> On 21.07.2014 12:41, Benjamin Franksen wrote:
>>> Why don't you just set DRVL=DRVH=<the desired value>.
>>
>>      /* check drive limits */
>>      if (prec->drvh > prec->drvl) {
>>          if (value > prec->drvh)
>>              value = prec->drvh;
>>          else if (value < prec->drvl)
>>              value = prec->drvl;
>>      }
>>
>> DRVL=DRVH => no check at all!
> 
> Strange. Not intuitive to me. And contrary to the docs.

That check predates the CVS history of the aoRecord.c file (1995). It
makes perfect sense to me, there has to be a way to disable the clipping
behaviour, and the assumption is that you would only create ao records
for things that you want to be able to actually change. If you want to
stop changes for a while, disable record processing using SDIS & DISV.

> This is from the
> RRM (https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14_Analog_Output#Desired_Output_Parameters):
> 
> """
> The VAL field's value is forced to be within the limits specified in the
> fields DRVH and DRVL, which are configured by the designer:
> 
> DRVL<=VAL<=DRVH
> 
> Note: If nothing is entered for DRVH and DRVL, the output value will
> never change.
> """

Wiki page fixed to document existing code.

- Andrew
-- 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System