FBNetworks in Devices and DeviceTypes?

[Jim Christensen]

Is anybody using the feature that you can put an FBNetwork in a Device
or DeviceType, or are you always just populating Devices and
DeviceTypes with Resources and putting the FBNetworks in the Resources
and ResourceTypes? I'm thinking of restricting the FBDK to just
handling FBNetworks in ResourceTypes and Resources only - this makes
the diagramming and managing of dependencies between DeviceTypes and
Devices much simpler.

By the way, the IEC 61131-3 syntax also permits only the configuration
of Resources within a PLC system (a Device in 61499 terms), or the
configuration of a single Resource as the Device, but not a mix of
Resources and Programs at the Device level.

Comments?
--
Best regards,
Jim Christensen

[christian]

Hi Jim,

I thought always this might be a bug inside FBDK and it is not allowed
by the standard, but I'm not sure about this. But at the end, my
colleagues and I never used this feature and as you say it would make
live easier. Also at the formal verification described at my book.
Furthermore, if I have a look at the book from Alois and at 4DIAC, I
think they also don't use this feature. Thus, I would remove it.

Christian

[Alois Zoitl]

Hi Jim,

I used this feature some time back when I worked on very small devices
with very little memory. There the approach of running applications
without resources has been quite helpful. In the meantime I drifted
away from this approach mainly because of the reason that I think the
resource approach gives a better structuring and understanding.
Although I often have just one application resource in the device
apart from the RMT_RES. Therefore for me it would be ok to remove this
feature even it is allowed by the standard (to answer also Christians
question). In 4DIAC we also do not allow it because of the same
reasons.

Alois

[James Christensen]

After some more digging, I found out the reason that we need to
support at least one feature of FBNetworks in Devices and DeviceTypes.
That is to allow the connection of an input variable of the device to
an input of a contained Resource. This is allowed by the 61499-1
syntax as currently amended, but the only mechanism for doing this
that is allowed in the 61499-2 LibraryElement DTD is the
DataConnections in an FBNetwork. The 61499-1 syntax also allows
specialized versions of other FB network elements, but that may be a
usage that could be deprecated in the future.

--
Best regards,
Jim Christensen