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

Subject: Re: EPICS Python client application survey
From: Andrew Johnson <anj@aps.anl.gov>
To: tech-talk@aps.anl.gov
Date: Wed, 30 Sep 2009 12:16:43 -0500
On Wednesday 30 September 2009 11:30:26 Benjamin Franksen wrote:
... several wise words, including:

> It /is/ a difference to the server whether you request DBR_SHORT, DBR_INT,
> or DBR_LONG. These will trigger different conversion routines, and thus
> might give different results.

I should add that the request type also affects the amount of data passing 
over the wire; if you request a large image with 8-bit pixels as a DBF_LONG or 
worse a DBF_DOUBLE array, you're going to be wasting network bandwidth and CPU 
time on the IOC converting all those individual 8-bit values into larger 
quantities.  Much better to do that conversion on the client.

I would encourage those working on this to read the release notes for R3.14.11 
as there are a couple of things we added which you guys are going to want to 
provide support for:
 * Long strings.  Important for accessing DBF_xxLINK fields since record names 
can be up to 60 characters long, so you can't always read or change the value 
of a link field using a 40 character DBF_STRING.
 * DBE_PROPERTY events.  Generated now on the VAL field of the mbb[io] record 
types when someone changes one of the *ST fields, a DBE_PROPERTY monitor 
allows a client to always know what the current ENUM strings are.

- Andrew
-- 
The best FOSS code is written to be read by other humans -- Harald Welte


Replies:
Re: EPICS Python client application survey Michael Abbott
References:
Re: EPICS Python client application survey Matt Newville
Re: EPICS Python client application survey Benjamin Franksen

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