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Execution flow in VEE

Question asked by VRFuser on Mar 23, 1997

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Hello everyone,

     Many thanks for all your suggestions. As many of you suggested, the
     answer was to use 'Sample and Hold' objects.

     Thanks once again,
     Warren

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VRFuser Mar 20, 1997 4:24 PM
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from: Greg Goebel / HP-MXD
      gvg@lvld.hp.com / 970-679-2305 / FAX 970-679-5971
to:   Warren Pickles
date: Friday, 21 March 1997 0823 MST

Sir:

Got a simple example program I can inspect?

[%%] regards -- gvg

--------------------------------- cut here ----------------------------------

>      Hello everyone,
>
>      I'm confused about execution flow in VEE. I had always understood
>      that once an object has received data at all its input pins, and its
>      sequence input pin has been 'pinged', it will execute. It may not be
>      the next object to execute, but it WILL execute.
>
>      However, I have been working on a userfunction that contains a
>      userobject (called 'SaveResultsToFile') that meets the above criteria
>      but never executes. As soon as the sequence input pin on
>      SaveResultsToFile is pinged, the userfunction exits. All the input
>      data is there. There are no Exit UserObjects until after
>      SaveResultsToFile.
>
>      Does anyone know of any circumstance where an object will not execute
>      despite all its inputs being satisfied? Perhaps I have a subthread
>      somewhere that is holding up execution in some way. Perhaps my
>      assumptions (in the first paragraph) are incorrect.
>
>      I have found a workaround, which is to have all the data input pins on
>      SaveResultsToFile being fed by Get Global objects, the globals being
>      set earlier in the userfunction. However, this is messy, and bad
>      programming practice, and anyway I would prefer to understand what's
>      going on.
>
>      Unfortunately the userfunction is rather complicated, so I can't
>      reproduce it fully here, but here is a rough sketch. I would
>      welcome any thoughts.
>
>
>      +-------+
>      | Until |
>      | Break |------------------------+
>      +-------+                        |
>          |              +-------------------------------+
>          |              | Main part of userfunction,   |
>          |              | which captures readings from |   data
>          |              | an instrument.               |----------+
>          |              | At some point, this loop     | output |
>          |              |    breaks.                    |          |
>          +-------+      +-------------------------------+          |
>                  |                                                 |
>       +------------------------------------------------------------+
>       |          |
>       |    +-------------------+
>       |    |   userobject      |
>       +----| SaveResultsToFile |
>            +-------------------+
>
>
>      The data output is being continuously generated, i.e. updated with each
>      reading, but this shouldn't cause my problem.
>
>      Regards,
>
>      Warren Pickles
>      M/A-Com Eurotec, Cork, Ireland
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VRFuser Mar 20, 1997 6:10 PM
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Hello Warren,

I have had these things happen to me many times. In all but two
cases it has been my own fault in thinking the inputs were satisfied
when they weren't or the inputs were not the right type or there
was an error in the function being called.
In you case I would inspect the inside of SaveResultsToFile:
put a breakpoint on it, then turn on the execution flow and data
flow viewing ON, then single step through the function; My guess
is, you'll find the problem is the function somewhere.

In the cases where I found the problem in VEE, it had to do
with loops which had feedback; the loops would exit prematurely
with NO error whatsoever! The solution was to put the loop
into a User Object with the feedback external to User Object.

Regards

Rob Marquardt
System Test Engineering
Rockwell Automation / Allen-Bradley
Milwaukee, Wisconsin, USA

----------
From: Warren Pickles
Sent: Friday, March 21, 1997 5:36 AM
To: hpvxd_xc
Subject: Execution flow in VEE

     Hello everyone,


     I'm confused about execution flow in VEE. I had always understood
     that once an object has received data at all its input pins, and its

     sequence input pin has been 'pinged', it will execute. It may not
be
     the next object to execute, but it WILL execute.


     However, I have been working on a userfunction that contains a
     userobject (called 'SaveResultsToFile') that meets the above
criteria
     but never executes. As soon as the sequence input pin on
     SaveResultsToFile is pinged, the userfunction exits. All the input
     data is there. There are no Exit UserObjects until after
     SaveResultsToFile.


     Does anyone know of any circumstance where an object will not
execute
     despite all its inputs being satisfied? Perhaps I have a subthread
     somewhere that is holding up execution in some way. Perhaps my
     assumptions (in the first paragraph) are incorrect.


     I have found a workaround, which is to have all the data input pins
on
     SaveResultsToFile being fed by Get Global objects, the globals being

     set earlier in the userfunction. However, this is messy, and bad
     programming practice, and anyway I would prefer to understand what's

     going on.


     Unfortunately the userfunction is rather complicated, so I can't
     reproduce it fully here, but here is a rough sketch. I would
     welcome any thoughts.




     +-------+
     | Until |
     | Break |------------------------+
     +-------+                        |
         |              +-------------------------------+
         |              | Main part of userfunction,   |
         |              | which captures readings from |   data
         |              | an instrument.               |----------+
         |              | At some point, this loop     | output |
         |              |    breaks.                    |          |
         +-------+      +-------------------------------+          |
                 |                                                 |
      +------------------------------------------------------------+
      |          |
      |    +-------------------+
      |    |   userobject      |
      +----| SaveResultsToFile |
           +-------------------+




     The data output is being continuously generated, i.e. updated with
each
     reading, but this shouldn't cause my problem.


     Regards,


     Warren Pickles
     M/A-Com Eurotec, Cork, Ireland
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VRFuser Mar 20, 1997 6:15 PM
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Hello everyone,

     I'm confused about execution flow in VEE. I had always understood
     that once an object has received data at all its input pins, and its
     sequence input pin has been 'pinged', it will execute. It may not be
     the next object to execute, but it WILL execute.

     However, I have been working on a userfunction that contains a
     userobject (called 'SaveResultsToFile') that meets the above criteria
     but never executes. As soon as the sequence input pin on
     SaveResultsToFile is pinged, the userfunction exits. All the input
     data is there. There are no Exit UserObjects until after
     SaveResultsToFile.

     Does anyone know of any circumstance where an object will not execute
     despite all its inputs being satisfied? Perhaps I have a subthread
     somewhere that is holding up execution in some way. Perhaps my
     assumptions (in the first paragraph) are incorrect.

     I have found a workaround, which is to have all the data input pins on
     SaveResultsToFile being fed by Get Global objects, the globals being
     set earlier in the userfunction. However, this is messy, and bad
     programming practice, and anyway I would prefer to understand what's
     going on.

     Unfortunately the userfunction is rather complicated, so I can't
     reproduce it fully here, but here is a rough sketch. I would
     welcome any thoughts.


     +-------+
     | Until |
     | Break |------------------------+
     +-------+                        |
         |              +-------------------------------+
         |              | Main part of userfunction,   |
         |              | which captures readings from |   data
         |              | an instrument.               |----------+
         |              | At some point, this loop     | output |
         |              |    breaks.                    |          |
         +-------+      +-------------------------------+          |
                 |                                                 |
      +------------------------------------------------------------+
      |          |
      |    +-------------------+
      |    |   userobject      |
      +----| SaveResultsToFile |
           +-------------------+


     The data output is being continuously generated, i.e. updated with each
     reading, but this shouldn't cause my problem.

     Regards,

     Warren Pickles
     M/A-Com Eurotec, Cork, Ireland
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VRFuser Mar 21, 1997 11:50 PM
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In message <199703211129.AA064243740@relay.hp.com>, Warren Pickles
<picklesw@macom.com> writes
>     Hello everyone,
>
>     Does anyone know of any circumstance where an object will not execute
>     despite all its inputs being satisfied? Perhaps I have a subthread
>     somewhere that is holding up execution in some way. Perhaps my
>     assumptions (in the first paragraph) are incorrect.
>
>
>     Regards,
>
>     Warren Pickles
>     M/A-Com Eurotec, Cork, Ireland
>
I've found sometimes that and object doesn't seem to operate because,
while all of it's inputs are satisfied, they're not all satisfied at
*the same time*.

It seem you can examine the input threads and they all show valid data
but the userobject won't execute as expected.

The workaround I used for this was to pass all the inputs through gates
and ping all the execution inputs of them when I know that all my inputs
are as I want them, and I want the userobject to execute.

Hope this helps.

--
Gerry Murray
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