Hi all,
I decided to start a new thread to answer to Sebastians mail below regarding
the Plc4X JPA Like layer.
First, I think, we should get a feeling of what we all think this layer could
or should do and what kind of features we want to incorporate there.
From my perspective this layer should allow the following:
1. Provide access to fields via “symbolic names” or aliases. They could be
provided by the system (S7CommPlus) or they could be registered with the
“EntityManager”
2. Annotations for POJOs “PlcEntities”
I Imagine something like
@PlcEntity
class Pojo {
@PlcTimestamp
private long timestamp;
@PlcField(“%DB8:DBL4:INT”)
private int value;
}
Of course this is a very first sketch but I suggest to collect our ideas on a
Confluence to develop the idea “over time”.
Best
Julian
Am 24.08.18, 09:03 schrieb "Sebastian Rühl"
<sebastian.ruehl...@googlemail.com.INVALID>:
Hi Julian,
Depending on the type of change this might something I could implement to
ADS locally if its just a change of the Address format.
Chatting with Chris we stumbled over the size attribute in a
ReadRequestItem. This might become obsolete too as in its form right now it
isn’t that helpful.
FYI: I was about to read something like this from the plc
https://infosys.beckhoff.com/index.php?content=../content/1031/tcplclibutilities/html/tcplclibutilities_timestruct.htm&id=
<https://infosys.beckhoff.com/index.php?content=../content/1031/tcplclibutilities/html/tcplclibutilities_timestruct.htm&id=>
What we can see here that we need read 8 words from the plc. We can do that
by suppling the IndexGroup/IndexOffset and a Length(ADS) of 16 Bytes. Then I
would need to chunk the response into 2 bytes. Im still not sure if this is
something I would integrate into the plc4x directly or into a layer above aka
JPA/Plc4xJPA (Java Persistence Layer alike) [maybe for the basic structs of ADS
it might be worth it]. Then there are complex types which are mixed
https://infosys.beckhoff.com/index.php?content=../content/1031/tcplclibutilities/html/tcplclibutilities_timestruct.htm&id=
<https://infosys.beckhoff.com/index.php?content=../content/1031/tcplclibutilities/html/tcplclibutilities_timestruct.htm&id=>.
Here a chunking into 8 would not work as you would need to read fixed
different chunks (aligned to it type) from a byte stream. For this I would then
use a „RAW“ read and slice it in the application level (or PLC4XJPA).
Maybe working on the Plc4xJPA (working title you name it ;) would be a good
idea to get some impression of requirements from that side too (I’ll will scope
that on my next TODOs).
What is still missing in your PR suggestion „3) Define 2 types of
ItemRequest/-Responses:“. But that might be ok as these changes are an addition
to that and as I wrote in the first sentence this might be local to the S7
address format in the first step anyway so in my opinion you are good to go
(Maybe leave out the renaming of the query for now to keep the PR footprint a
bit lower).
Regarding API design: Its hard. It should be simple yet powerful. So if the
first iteration doesn’t fit well we just refactor it :)
Sebastian
