Re: StreamDevice device locking

[Dirk Zimoch via Tech-talk <tech-talk@aps.anl.gov>]

Or maybe the libs don't match between my build system and your system. I 
will check.
On 08.02.19 14:49, Dirk Zimoch wrote:
> 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