Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Wed, 11 Apr 2012 09:53:01 +0200

Hi Jeff, Florian,

I checked my presentation and found:

* Single-threaded context
  - Callbacks are only called from within a ca_* function.

 The program must call ca_pend_io(), ca_flush_io(), ca_pend_event()

or ca_poll() regularly to receive any data (e.g. in event/idle loop).

This is wrong:
ca_flush_io() will not do the job because it does not handle input.
ca_pend_event() is definitely ok here.
ca_poll() is ca_pend_event(1e-12) and thus is ok.

ca_pend_io() waits for search and get without callbacks but probably not

for monitors? Jeff, please comment.

Dirk

Hill, Jeffrey O wrote:

Hi,

Correct, a single-threaded CA client code must periodically spend some time in ca_pend_event() in order that the channels will connect. The channels will not transition from a disconnected to a connected state if your main thread doesn't periodically call ca_pend_event. The ca_pend_event(), among other tasks, arranges for the incoming TCP messages to be processed, and calls the user callbacks.

The ca_flush_io() call is forcing all of the en-queued put/get/subscribe requests to be delivered to the TCP circuits in aggregate, but does not necessarily process the incoming messages on the TCP circuits, or call the connection callbacks.

Jeff

-----Original Message-----
From: Florian Feldbauer [mailto:[email protected]]
Sent: Monday, April 02, 2012 8:05 AM
To: Hill, Jeffrey O
Cc: EPICS tech talk
Subject: Re: What is void* puser in ca_create_channel

Hey,

after creating all channels and subscriptions I used ca_flush_io() in my
program as
mentioned in the talk "Channel Access Client Programming" from Dirk
Zimoch at the last
EPICS meeting at PSI.
When I use ca_pend_event() instead, the CA is working.

Best regards,
Florian

On 03/30/2012 04:10 PM, Hill, Jeffrey O wrote:

Just one other question: Can I use the CA methods ca_create_channel and
ca_create_subscription within a c++ class?

Yes, the necessary 'extern"C"' bracketing is in the ca header files so

that its C interface can be called from C++.

Any idea based on this few information, or should I post my code?

If the CA client and its IOC are not on the same subnet then you may

need to add the IOC's address to the EPICS_CA_ADDR_LIST environment
variable for the client. Otherwise, if they are intended to be on the same
subnet them make certain that both hosts are configured with the same
subnet mask.

There are also some additional suggestions in the troubleshooting

section of the CA reference manual.

Jeff

-----Original Message-----
From: Florian Feldbauer [mailto:[email protected]]
Sent: Friday, March 30, 2012 6:29 AM
To: Hill, Jeffrey O
Cc: EPICS tech talk
Subject: Re: What is void* puser in ca_create_channel

Thanks for your answers.

Just one other question: Can I use the CA methods ca_create_channel and
ca_create_subscription within a c++ class?
The project we are working on should use OO techniques.
We need not only an interface to EPICS, but also to a simulation.
So we wanted to have an abstract base class, which is used by the rest
of our project, and  derived classes for the implementation of
the individual "control systems". One derived class would contain the

CA

for EPICS and another the interface to our simulation.

I can compile my test program for this object-structure, but I don't

get

a conncetion to my EPICS ioc.
The two examples from makeBaseApp.pl are working correctly.

Any idea based on this few information, or should I post my code?

Best regards,
Florian

On 03/29/2012 05:19 PM, Hill, Jeffrey O wrote:

Hi,

The puser pointer you pass to ca_create_channel is saved by the

library

with the channel and is later supplied as a puser argument to your

channel

connectione state update callback function. There is also a ca function
"void * ca_puser ( CHID )" that will return the puser pointer that was
supplied when the channel was created.

Likewise, the puser pointer you pass to ca_create_subscription is

saved

by the library with the subscription and is later supplied as a puser
argument to your subscription update callback function.

How does this parameter have to look like?
Can I use a C-Struct with any member I want to have (even members

which

are not for the CA, but for another part of my program)? Are there

any

members which are mandatory? (like value or chid)

A pointer to any data structure can be used. The CA library does not

in

any way access, or place any restrictions on the content of, this user
application private data structure. The user application is of course
responsible for allocation, initialization, maintenance, and de-

allocation

(proper cleanup) of this data structure.

Use of void pointers passed to callbacks is an old technique which is

roughly equivalent to a virtual function in modern software interfaces,
BTW.

HTH, and feel free to send any other questions that you might have,

and

I will do my best to answer them.

Jeff

-----Original Message-----
From: [email protected] [mailto:tech-talk-

[email protected]]

On Behalf Of Florian Feldbauer
Sent: Thursday, March 29, 2012 4:01 AM
To: EPICS tech talk
Subject: What is void* puser in ca_create_channel

Dear all,

I currently write a CA Client that should monitor all measured
temperatures in my experiment
to regulate the chillers.
This is my first try to program a CA Client, and I have a question
concerning this:

The ca_create_channel and the ca_create_subscription methods both

have

a parameter void* puser. How does this parameter have to look like?
Can I use a C-Struct with any member I want to have (even members

which

are not
for the CA, but for another part of my program)? Are there any

members

which are mandatory? (like value or chid)

In the camonitor.c example generated with makeBaseApp.pl this puser

is

just a pointer to a C-Struct containing
a c-string value, the chid and evid of the channel.

Best regards,
Florian

--
-------------------------------------
| Florian Feldbauer                 |
| Ph.D. student                     |
|                                   |
| Institut für Experimentalphysik I |
| Ruhr-Universität Bochum           |
| Universitätsstr. 150              |
| D-44780 Bochum                    |
|                                   |
| Office: NB 2/173                  |
| Phone:  (+49)234 / 32-23538       |
| Fax:    (+49)234 / 32-14170       |
| Web:    http://www.ep1.rub.de     |
-------------------------------------

--
-------------------------------------
| Florian Feldbauer                 |
| Ph.D. student                     |
|                                   |
| Institut für Experimentalphysik I |
| Ruhr-Universität Bochum           |
| Universitätsstr. 150              |
| D-44780 Bochum                    |
|                                   |
| Office: NB 2/173                  |
| Phone:  (+49)234 / 32-23538       |
| Fax:    (+49)234 / 32-14170       |
| Web:    http://www.ep1.rub.de     |
-------------------------------------

--
-------------------------------------
| Florian Feldbauer                 |
| Ph.D. student                     |
|                                   |
| Institut für Experimentalphysik I |
| Ruhr-Universität Bochum           |
| Universitätsstr. 150              |
| D-44780 Bochum                    |
|                                   |
| Office: NB 2/173                  |
| Phone:  (+49)234 / 32-23538       |
| Fax:    (+49)234 / 32-14170       |
| Web:    http://www.ep1.rub.de     |
-------------------------------------

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System