Experimental Physics and
Industrial Control System

Florian Feldbauer <[email protected]> · Tue, 26 May 2015 15:52:29 +0200

Hey Ralph,

yes, I experienced such a problem for my current device support
for our iseg HV modules.
There I'm also using the asynPortDriver (one driver per module).
For "small scale" systems (about one crate) it works,
but with larger setups we also have problems with the port-locking...

For the new device support I'm currently working on, this is no issue,
since now I don't have any hardware i/o at all.
iseg is providing their so called Hardware Abstraction Layer which works
as a daemon collecting and caching all the parameters of the
connected HV modules.
The device support just communicates with the daemon to get the cached
values or queue new values to be send by the daemon, respectively.

But looking at your first reply to this topic, programming a thread
checking if any set-values have changed and updating the corresponding
output-records seems not too hard. So maybe I will try to write
the device support myself and keep the asynPortDriver as backup solution.

Cheers
Florian

On 05/26/2015 02:46 PM, Ralph Lange wrote:
> Hi Florian,
> 
> Yet another thing to keep in mind is the level at which you want locking
> of things to happen.
> Usually (in the blocking case), a port driver locks its port, does the
> IO, then unlocks its port.
> 
> Some years ago at BESSY we were thinking how our CAN-Bus driver would
> fit the ASYN model. CANopen compliant, i.e. many nodes per bus (~30),
> many variables per node (~15), and some types of indexed variables with
> many values per variable (~120).
> The only thing that we wanted to be locked (between request and reply)
> was the variable, to avoid sending commands on two different indexes of
> the same variable without waiting for an answer.
> Something like that does not fit the ASYN model well. For each fully
> populated bus segment you would basically end up with ~450 instances of
> a blocking "variable" port driver, all talking to the same non-blocking
> lower level "bus" port driver. Starting 450 threads per bus made this
> look very unattractive.
> In the end we kept our patchwork non-ASYN driver, as (for this and other
> reasons) the rewriting effort was not justified well enough.
> 
> ~Ralph

-- 
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| Dr. Florian Feldbauer                |
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| Helmholtz-Institut Mainz /           |
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System