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Subject: Re: imageRecord
From: "Leonard J. Reder" <[email protected]>
To: Ned Arnold <[email protected]>
Cc: EPICS Tech-Talk <[email protected]>
Date: Thu, 24 Feb 2000 09:54:49 -0800
Ned,

I now have a modified version of your image record working and async
device support for my DataCell board grabbing frames.  I am going to
attempt to use the genSub record to connect a subroutine now.  Do you
have any example code that shows an implementation of what you discussed
below.

Thanks,

Len

Ned Arnold wrote:
> 
> Hey Len,
> 
> > Thanks for the reply,
> >
> > A couple of quick questions:
> >
> > What was the intended purpose of the enab and rate fields?
> 
> These were implemented as safe guards to "throttle" the transferring of
> the entire image to a client. In my application, the client will fetch
> the image whenever the VAL field of the image record changes (increments).
> So, if ENAB (enable) is set to 0, the VAL field will not increment even if
> something processes the image record. One would set ENAB to 0 if the image is
> known to be invalid (maybe the camera is off!).
> 
> The RATE field sets a minimum time between increments of the VAL field.
> If the image record scans at 10 Hz (because of a database flub up) and
> RATE is set to .49, the VAL field will only increment at 2 hertz, thereby
> "throttling" the client's fetching of an image. Set RATE to 0 for
> no throttling.
> 
> Both of these are a result of my paranoia of swamping the network with
> image data. Ignore them if you don't have the same fears.
> 
> >
> > I understand the vxnm now and I actually have two different versions
> > of your record code.  If I add pimg field as you suggest is this just
> > another DBLINK or how do I specify it in the ImageRecord.dbd file?
> 
> Marty Kraimer had a better idea than "exporting" the pointer through
> a record field. Your subroutine can find out all the information it
> needs about .L0 (the pointer to the first pixel) by using the database
> access routines described in Chapter 12 of the EPICS IOC Application
> Developer's Guide. Specifically, if you call dbGetPdbAddrFromLink(for INPn)
> (Pg 138) from your subroutine record, you get all the "dbAddr" information
> described on pg 129, including the address of the field. This would allow
> you to find the image without passing any of the image data around. I
> agree that this is probably the best way to meet your need.
> 
> For example, if the subroutine record had input links defined for ...
> 
> INPA   image_record_1.L0
> INPB   image_record_1.XRES
> INPC   image_record_1.YRES
> INPD   image_record_1.SIZE
> 
> your analysis routine could find out all the information about the image
> without duplicating any definition of it.
> 
> Hope this helps ...
> 
>         Ned
> 

-- 
____________________________________________________
Leonard J. Reder
Jet Propulsion Laboratory
Interferometry Systems and Technology Section 383
Email: [email protected]
Phone (Voice): 818-354-3639
____________________________________________________


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