Re: waveform record question

[Marty Kraimer <mrk@aps.anl.gov>]

I think BUSY should just be ignored for any new device support. RARM may be useful.

My guess is that both of these fields were created to support a transient 
recorder (TR). By TR I mean a device that when armed and triggered: samples data 
from an ADC, stores that values in memory residing in the TR, and after a 
specified number of samples generates an interrupt. Typical device support for a 
TR will read the TR memory when the interrupt occurs. The RARM field can be used 
by device support to decide if the recorder should be automatically rearmed.

I looked at the existing device support in 3.13 base that uses the busy field: 
devWfComet, devWfJoergerVtr1, and devWfXy566Sc. In each case it looks to me like 
they could have been written so that they did not need the busy field. Each of 
these records were written before PACT even existed so BUSY may be a 
evolutionary artifact.

Marty Kraimer


Pedro Gigoux wrote:

> Hi Kay,
>
> Thanks for the input. I was looking at the waveform record process()
> routine and found that BUSY is used there. The following is the relevant
> part of the code:
>
>         if ( pact && pwf->busy ) return(0);
>
>         status=readValue(pwf); /* read the new value */
>
>         /* check if device support set pact */
>         if ( !pact && pwf->pact ) return(0);
>
>         pwf->pact = TRUE;
>
> 	[do housekeeping stuff]
>
> 	pwf->pact = FALSE;
> 	return (0);
>
> Suppose that we have asynchronous device support. The first time the
> record processes PACT is FALSE and readValue() is called. If the device
> is not ready to send data the device support routine sets PACT=TRUE and
> sets a watchdog timer to call process() in the future. Now, if for any
> reason BUSY=TRUE as well, the next time process() is called it won't
> call readValue(), and PACT and BUSY will remain TRUE forever. Since
> readValue() is not called, no timer is set to call process again. Thus,
> the record will remain in active state, but not executing. This is
> exactly what I saw when I set BUSY=TRUE in my device support routine.
>
> Regards,
> Pedro.
>
> Kay-Uwe Kasemir wrote:
>
> > Hi:
> >
> > They are both "private" for your device support routine.
> > As far as I know, there is no predefined meaning.
> >
> > You can e.g. use "busy" so that your device support
> > can indicate to users that it's armed, waiting for a trigger
> > but hasn't received one, yet.
> >
> > RARM = re-arm can be used to tell your device support
> > that it should re-arm (wait for another trigger)
> > once it got data.
> >
> > If you don't use them because it doesn't make
> > sense for your device: fine.
> >
> > Thanks,
> > -Kay
> >
> > At 03:05 PM 4/9/2002, pedro wrote:
> >
> > > Hi,
> > >
> > > Could someone give me an explanation on how to use the RARM and BUSY
> > > fields in the waveform record? Why do we need a BUSY field if we already
> > > have PACT? I'm writing a device support routine to read a serial port
> > > using the waveform record and I'm not sure how to use these fields. I
> > > found that about half of the device support routines in the EPICS
> > > distribution doesn't use them at all. The documentation doesn't say much
> > > either.