Experimental Physics and
Industrial Control System

Dirk Zimoch via Tech-talk <[email protected]> · Fri, 8 Feb 2019 14:49:39 +0100

I just remembered that with GPIB the whole bus is basically locked while

a device is addressed. This is typically the case while the IOC is

waiting for a reply. The device is addressed as a "talker" during this

time. So no other device can use the bus. Thus it is a limitation of

GPIB that you cannot really interlace communication with multiple devices.

I thing one could make it work if the device can send SRQ when it has a

reply. So the IOC would only address the device when it has actually

something to talk. But that is probably more effort to implement than

it's worth.

Dirk

On 08.02.19 14:40, Dirk Zimoch via Tech-talk wrote:

The question is: Is there a way to tell *asyn* to block only on the

address level?

This may depend on the implementation of the particular asyn interface.

I do not have any devices with addresses at the moment. (Only GPIB comes

to my mind.) So I cannot test.

StreamDevice calls pasynManager->blockProcessCallback() with its

asynUser handle. The asynUser handle is bound to an address on a port.

So I had expected that asyn blocks only that address, not others on the

same port.

I have to set up a GPIB system with at least 2 devices first before I

can test this case.

Dirk

On 08.02.19 14:24, Joao Afonso via Tech-talk wrote:

Hello,

At the moment I am experimenting with StreamDevice, while connecting

it to a custom asynPortDriver (instantiated with ASYN_MULTIDEVICE,

ASYN_CANBLOCK).

According to the documentation, each protocol command blocks the

device for the duration of the protocol, which makes sense.

But an access to two devices on two different addresses should be

possible:

http://epics.web.psi.ch/software/streamdevice/doc/processing.html

  * /"The first |out| command in the protocol locks the device for
    exclusive access. That means that no other record can communicate
    with that device. This ensures that replies given by the device
    reach the record which has sent the request. _On a bus with many
    devices on different addresses, this normally locks only one
    device_. The device is unlocked when the protocol terminates.
    Another record trying to lock the same device has to wait and might
    get a |LockTimeout|." /

However, I noticed that if I process two records with stream device,

for addresses #1 and #2, it first runs all callbacks for address #1,

and only after to #2.

This is contrary to my expectation, which would be to see callbacks to

both devices being executed interleaved.

Is there a way to tell StreamDevice to block only on the address

level, allowing to different addresses to be processes simultaneously?

Thanks,
Joao Afonso
CERN TE-EPC-CCS

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System