Hey Chris,
please, take my words more as observations than as criticism.
I am really impressed by the current state of the project with regard to coding
styles and especially architecture. And I think it is great that your company
supports this project that massively.
I had now a deep look inside the code (unfortunately I have no S7 here for some
"live" debugging) and I think I understand the control flow now. I never used
netty before and was a bit confused by the message conversion and it took me a
while to get the complete flow from request to the S7 ; )
And of course I totally understand that one concentrates on features more than
on documentation (who doesn't?).
And if it's okay for you I would open a branch and add some comments or small
refactorings that I see while going through the code that you can then review
and hopefully integrate.
How do you currently manage the contributions, feature branches and PRs or
repository forking?
I also observed that the jira seems a bit orphaned (again no criticism, just
observation!) and if it's okay for you I will open one or two tickets for the
our needs (the batch processing) that we can have a discussion or specification
there.
Best
Julian
Am 27.07.18, 16:01 schrieb "Christofer Dutz" <christofer.d...@c-ware.de>:
Hi Julian,
you are absolutely correct, that our documentation leaves quite some room
for improvement ;-)
Currently being funded by my company for working on this, I was
concentrating on getting PLC4X to an initially usable state and have to admit
that I did sacrifice documentation for features in the past.
But if we want to grow the community, documentation is of essential value.
I promise to start writing more documentation. Probably some simple user
documentation would be the best starting point.
I will increase my efforts ... promised :-)
For now, you could have a look at the Kafka Bridge example as this builds a
PlcReadRequest with multiple items (separate addresses).
Chris
Am 26.07.18, 16:54 schrieb "Julian Feinauer" <j.feina...@pragmaticminds.de>:
Hi Chris and hi Sebastian,
thank both of you for the happy welcoming.
@Chris
Thank you for your hints, I went a bit into the code but the thing I'm
currently missing (is there a central documentation) is how one can request a
larger portion of memory (possible even multiple PDUs).
As my understanding of the API is that I can only request single Values?
Where is the best place to get a good insight into the API (docu or
code)?
Thanks!
Julian
PS.: I'm also mathematician but went more for statistics and number
theory (beautiful but mostly unusable) but we have done some stochastic
optimization (which is especially strong for high dimensional problems) so I
can definitively try to assist in solving the problem
Am 26.07.18, 14:51 schrieb "Christofer Dutz"
<christofer.d...@c-ware.de>:
Hi Julian,
welcome to our list ( ... reading your post definitely made my day
(Even if I thought it couldn't get better)
Regarding your first Idea ... this is definitely on my mind and was
taken into consideration when implementing the S7 driver.
Right now the S7MessageProcessor interface provides an extension
point for things like this. Currently there is only one implementation. The
DefaultS7MessageProcessor is used to automatically split up large reads and
writes into multiple requests depending on the negotiated max PDU size. This
would be the place to re-write the S7Message requests to do what you are
planning on doing. I was planning on getting a friend of mine on board to
address this sort of thing (She's a mathematician, specialized on packing and
optimization problems), but if you are interested and want to work on this, I
would be glad to help you with this. I think the only thing currently not
supported, is to read information which would exceed the PDU size if sent in a
single PDU.
Regarding batch reads and writes ... I think such a thing would be
a great extension. However we would need to be able to configure this sort of
thing. As this could be something that might confuse people, manually turning
batch reads/writes on and configuring this in the connection string would be a
good way to go. The way PLC4X is built up, it shouldn't be a problem to
implement something like this. The Plc4XS7Protocol class could simply queue
all read/write items and have a separate worker drain that queue. This could be
similar to the queuing implemented in the S7Protocol class, just the trigger
would be a different one (Eventually the driver could send some sort of Batch
operation heartbeat event). Here too I would be more than happy to help
implementing this.
Chris
Am 26.07.18, 13:59 schrieb "Julian Feinauer"
<j.feina...@pragmaticminds.de>:
Hey everybody,
first, a great compliment for starting this excellent project
and bringing it this far forward.
I am on the dev mailing list since some months and was
following the development very interested but was not able to give any input
due to other duties.
We are a small german start-up doing (at least some of) the IoT
and Industry 4.0 stuff everybody is talking about. Currently, we have our own
home-build implementation of the S7 protocol as we do a lot of communication
with Siemens PLCs.
We also had some discussions and ideas of a more general
interface as we start to incorporate other devices and protokolls in our stack.
And from my perspective PLC4J is the “ideal” approach and fits nearly perfect
with our ideas and thus, we are currently thinking about replacing our own code
with PLC4J and in turn, try to bring this project forward in the directions we
aim to go.
Thus, from my side a warm welcome to the community and all
contributors and I’m really looking forward for the discussions with you!
And let me start with a first idea of a feature, I think we
would need.
For a short background, we are doing a lot of interaction with
PLCs and usually read a lot of data (many variables) from the PLC with high
frequencies.
Thus, our approach is not to read single addresses and cast
them in one step but to read one connected memory region (datablock) and
extract all variables of interest from the block and cast them to the
respective types.
The main reason for this is to reduce the communication load on
the PLC side.
I hope that I’m not duplicating existing ideas or concepts but
I didn’t find anything specific to this problem.
To be able to switch to PLC4J my idea was to have a concept of
“Batch” Reads or Writes, kind of like the JDBCs batch mode.
This could have two variants. One would be the possibility to
give the driver a list of variables to read and the driver batches them as it
makes sense and then performs the read opaque and returns all the result.
The other option, especially in the async case could be that
the reader internally batches subsequent calls until certain thresholds (number
of commands, time limit) are met and then performs batched reads of consecutive
memory regions.
What do you think of this approach?
Best!
Julian
pragmatic industries
