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

Subject: RE: streamDevice: how to read a value as fast as possible?
From: Mark Rivers <rivers@cars.uchicago.edu>
To: "'Dirk Zimoch'" <dirk.zimoch@psi.ch>, "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Mon, 11 Feb 2013 20:27:52 +0000
> 2. If the device supports SRQ, this could in theory be used to trigger 
> the fetch record. But unfortunately gpib SRQ handling is asyn is broken 
> (or most properly never worked).

I have heard about a couple of problems with the asyn VXI-11 support.  If possible I would like to get these fixed before the next release of asyn, which is otherwise ready to go.

I don't have any experience with VXI-11, and don't own any VXI-11 devices myself.  But I think I could borrow one from elsewhere at the APS.

Those who have had VXI-11 problems with aysn:

- Can you please describe exactly the symptoms?  I seem to recall that the SRQ problem manifested itself as the IOC crashing if an SRQ was asserted when the IOC boots.  Is this true?  Do SRQs work otherwise?

- Can you give me a specific device and configuration that will reproduce the problem?  Hopefully a relatively common device like a digital scope that we may have here at the APS?

Thanks,
Mark


-----Original Message-----
From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Dirk Zimoch
Sent: Monday, January 07, 2013 7:33 AM
To: tech-talk@aps.anl.gov
Subject: Re: streamDevice: how to read a value as fast as possible?

On 21.12.2012 22:21, Martin Konrad wrote:
> Hi,
> I want to read out an LXI compatible power meter (Agilent N1912A) with
> StreamDevice. Depending on its configuration (averaging etc.) this
> device might need very different time to acquire a value. Nevertheless I
> always want the device to acquire data continuously. I also want to get
> the data with a time stamp that is close to the time the data
> acquisition was finished.
>
> Unfortunately I did not find a way to configure the device to send new
> (unsolicited) data as soon as acquisition is finished. But the device
> supports two read-out modes:
>
> 1. A synchronous "READ?" command that in some cases blocks for more than
> a minute. Running this command continuously is obviously not exactly a
> nice solution. But anyhow: Is there a way to issue the next "READ?"
> command right after the previous one finished?
> 2. A free-running mode (device automatically starts the next acquisition
> as soon as the first one is finished). In this mode the interface is
> never blocked and data can always be read out with the "FETCH?" command
> which immediately returns the last reading. Using this command with
> SCAN=".1 second" leads to a lot of unneeded record processing (as well
> as CA traffic to clients that monitor this PV and also archiving load).
> Is it possible to avoid processing of my ai record if the VAL field did
> not change? It seems to me that this is a limitation caused by the
> asynchronous behavior of Asyn/StreamDevice...
>
> Any ideas?
>
> Martin
>

1. Let the FLNK of your record point to its own PROC field and make it a 
CA link. Also set PINI YES to start the loop. Use a long ReplyTimeout, 
e.g. 600000 (= 10 minutes)

If you want to be able to start and stop the loop, let the SDIS link 
point to a bo record which acts as a switch. (But pending requests are 
not interrupted.) In order to restart the loop, let the FLNK of the bo 
record point to your original record's PROC field and make it a CA link, 
too.

2. If the device supports SRQ, this could in theory be used to trigger 
the fetch record. But unfortunately gpib SRQ handling is asyn is broken 
(or most properly never worked).

Dirk


References:
Re: streamDevice: how to read a value as fast as possible? Dirk Zimoch

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