Experimental Physics and
Industrial Control System

Ricardo Herrero <[email protected]> · Wed, 25 Feb 2015 09:56:18 +0100

Thank you all!

 You all have given me so much information, I have to review and study

the different codes you have told me and I will try to study the C++

code. At last I will try to implement it in Java, but I´ll give a try

first in C++ to see what´s going on. Thank you all again, when I´m done

with it, I will tell you, and surely I will have more questions.

Regards, Ricardo

El 2015-02-24 20:41, [email protected] escribió:

Hi Ricardo,

Kay's and Matt's advice is good.

The best way for you to get started is to look at the examples. I see
you've been looking at the Java examples, but I suggest you look at
the C++ code too. There are more examples there of what you're trying
to do.

Using monitors sounds like the right thing for you to be doing.

For the server-side you should definitely use pvDatabase. This will
avoid you having to write a lot of server code. pvDatabaseCPP has been
around for a while and a number of people have successfully used it
(e.g Kay's neutron server). There are a number of good examples in
pvDatabaseCPP. I'd start from exampleServer.

Marty Kraimer's also been developing pvDatabaseJava. Marty said today
this is now usable, so if you want to do Java you might try it out,
but bear you'll probably be the first real user. I've had a quick look
and there are some simple examples there in pvDatabaseJava/example.
I've just built it now and given the ExampleDatabase and HelloExample
examples a quick try and at a first look these seems to work OK.

You'll have to clone it from SourceForge:
hg clone http://hg.code.sf.net/p/epics-pvdata/pvDatabaseJava

You can get the latest of other modules there too.

There's not a client library yet, but there are a number of examples
of clients. There are those in pvAccessCPP (e.g. pvget has a monitored
version) as well as those in pvDatabaseCPP. I used longArrayMonitor in
arrayPerformance to get started with my clients.

There's also the neutron server/client mentioned  and another simple
client/server example I wrote, ntndarrayServer, in alphaCPP (clone in
the same way as pvDatabaseJava).

Just copy one of the examples and modify the requesters or if you use
the client.* code in ntndarrayServer you can create a MonitorCallback
and implement the processElement method. ntndarrayServer was just some
test code, but it may be a fast way to get going if you're going to do
a C++ client.

If you have any more questions I'll be happy to answer them.

Good luck.

Dave

________________________________________
From: [email protected] [[email protected]] on
behalf of Kasemir, Kay [[email protected]]
Sent: 24 February 2015 17:02
To: Ricardo Herrero
Cc: <[email protected]>
Subject: Re: Begginer with EPICSv4

Hi:

The ChannelRPC, I think, is for the RPC type of protocol interaction,
where you write some data and then receive a result, like a remote
procedure call.
For the basic 'get' or 'monitor' interactions that are similar to
Channel Access you don't use the ChannelRPC.

One example for a custom server and client can be found here:
https://github.com/kasemir/EPICSV4Sandbox

On Feb 24, 2015, at 5:46 AM, Ricardo Herrero
<[email protected]> wrote:

Hello all,

I´m a newbie in this environment and I´m trying to understand EPICSv4,

I have tried examples HelloWorld and rdbService from example JAVA in

the last release from EPICSv4-JAVA. Now I´m trying to make a classical

example of a PVServer generating data and clients trying to get it

automatically, so I have a pair of questions that maybe you can help

me to solve.

First: I think that I should try using Monitor to publish/suscribe for

automatic onChange working between a PVServer and a Client, AM I

right?

Second: The General architecture for monitor seems a bit complex to me

and I need some help to Undestand it. Here are my thoughts and I want

to Know if I´m right or where I´m mistaken:

First you start the client with ClientFactory.start(). In the client

side you need to get to a ChannelProvider (in this case "pva"). Then

you have to create a Channel from the Provider (but you need a

ChannelRequester and I don´t know if I just have to create the object

or find it in the net).

Continuining with the creation of a PVStructure you can then create

also the Monitor (But I don´t know if when I create the channel, this

channel has to be a ChannelRPC or not). Also, Is the requester of the

monitor the same as the requester of the Channel creation?.

They're not the same.
The ChannelRequester is used to learn about connection changes,
the ChannelGetRequester is used to receive the result of a 'get',
and the MonitorRequester is used to receive the monitors.

They're all based on the basic Requester that gets debug messages.
In
https://github.com/kasemir/EPICSV4Sandbox/blob/master/neutronsDemoServer/src/neutronClientMain.cpp
you can see how I used a virtual base MyRequester in all my requester
implementation.
You could create just one

class MyRequesterForEverything : public virtual Requester, public
virtual ChannelRequester, public virtual ChannelGetRequester, …

to act as a handler for all requests, if you wanted to do it that way.

Finally I don´t see the structure of the MonitorElement, and when I

create the Monitor, do I have to make a while loop where I write the

commando FOR for the monitor and get there the MonitorElement?

The MonitorRequester is called with one or more updates.
MonitorRequester::monitorEvent() needs to loop over the received
events, because you may get multiples within just one 'network
package'.

In the server side I´m even more lost, as I have seen the

createMonitor in ChannelRPC, but I can´t see any of the parameters

configuration (such as the term onChange) that it´s mentioned in the

documentation about Monitor.

We've so far based all our V4 server code on the pvDatabaseCPP
library, where updating a PVRecord will send out the monitors.
Again see the  EPICSV4Sandbox or Matt's recent email.

Thanks,
Kay

--
Doctorando i2a2
Jefe de Servicio de Instalaciones - CEDEX

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System