Experimental Physics and
Industrial Control System

"Meyer, Markus via Tech-talk" <tech-talk at aps.anl.gov> · Mon, 22 Apr 2024 13:33:56 +0200

Hi Torsten,

my test system using the epics-twincat-ads driver is running now without issues and the readback is working as expected like you said. Once I got the "adsAsynPortDriver::drUserCreate: Parameter created: "ADSPORT=851/GVL.var?"" (index 1) output message everything started working. 

The problem was, that I specified the driver info without commas, e.g. "field(OUT, "asyn($(PORT) 0 1)$(ADSPORT)/GVL.var?") is wrong, but "field(OUT, "asyn($(PORT),0,1)$(ADSPORT)/GVL.var?")" is correct. Not using commas will cause the sscanf() in https://github.com/EuropeanSpallationSource/epics-twincat-ads/blob/045f40f2e80057025befe015b89b80288157c479/adsApp/src/adsAsynPortDriver.cpp#L1338 to fail silently.

Thanks again for your help.
Markus

-----Ursprüngliche Nachricht-----
Von: Torsten Bögershausen <tboegi at edom.se> 
Gesendet: Montag, 22. April 2024 06:12
An: Meyer, Markus <m.meyer at hzdr.de>; tech-talk at aps.anl.gov
Betreff: Re: AW: Readback of output variables in adsDriver

Hej again,

I haven't manage to find the time to set up a test system yet - hope that you have more luck.

Here are the good news.
After chatting with out expert:
epics-twincat-ads does support read back of output records !

One precondition is the '?' at the end of the OUT field:

<https://github.com/EuropeanSpallationSource/epics-twincat-ads/blob/045f40f2e80057025befe015b89b80288157c479/adsExApp/Db/adsTestAsyn.db#L12>

The "SetFAmplitudeRB" record should do what you ask for:
Writing to the EPICS PV changes the value in the PLC.
Once the value in the PLC is changed, that change should be seen in the output record.

HTH - and please let us know, how it goes.

On 2024-04-15 18:21, Torsten Bögershausen via Tech-talk wrote:
> Hej all,
> 
> I did have a short look into the driver - adsTestAsyn.db does have a 
> READBACK, but I couldn't find anything in the code, to switch it on or 
> off.
> But I know for sure, that people from SLAC have contributed a bulk 
> read, so far only 1Hz.
> Similar to Jure's driver, so far nobody had asked seriously enough for 
> READBACK so no time had been invested here.
> 
> Having said that, why do you not get any data ?
> 
> Wrong "ads port" ?
> I sometimes run wireshark to find out, what is going on.
> 
> /Torsten
> 
> 
> 
> On 2024-04-15 16:54, Meyer, Markus via Tech-talk wrote:
>> Hello Jure, Mark and Torsten,
>>
>> Thank you all for your responses and explanations of the 2 cases.
>>
>>> I kindly ask you to open a pair of issues on the Github repo. I 
>>> can't say when we we'll be able to take a closer look (we're 
>>> stretched pretty thin right now), but having open issues helps raise the priority.
>> I will do that and maybe I can help with some code after I have 
>> finished my evaluation of the other available drivers.
>>
>>> Case 2, at least, is probably not that hard to implement. Case 1, on 
>>> the other hand, is a bit thornier because of the design of the driver.
>> It may be OK to do the readback after iocInit only in a cyclic interval.
>>
>>> We here at ESS use a different driver for ADS, and if that one can 
>>> do the readback ? I haven't checked - but I highly suspect that it doesn't.
>> I have compiled the latest source of the driver from ESS [1] and can 
>> connect to my plc but unfortunately I get no values from the plc at 
>> all. I am still investigating what I am doing wrong here. I expect a 
>> readback because it's explicitly mentioned in the adsTestAsyn.db of 
>> adsExApp.
>>
>> Thanks,
>> Markus
>>
>> [1]
>> https://urldefense.us/v3/__https://github.com/EuropeanSpallationSourc
>> e/epics-twincat-ads__;!!G_uCfscf7eWS!cWY-oNbq-4U-gg1N5Q8SvI_E4DLNAd9t
>> Vgk5xrioIeV8ejfmVohmnmNpsp_rKDUJGlJGz2RJXqJ_poyPHDdx8g$
>>
>>
>> -----Ursprüngliche Nachricht-----
>> Von: Tech-talk <tech-talk-bounces at aps.anl.gov> Im Auftrag von Jure 
>> Varlec via Tech-talk
>> Gesendet: Montag, 15. April 2024 12:49
>> An: tech-talk at aps.anl.gov
>> Betreff: Re: Readback of output variables in adsDriver
>>
>> Hello Markus,
>>
>> Mark made a nice breakdown of the two cases. Right now, the adsDriver 
>> module supports neither. We are aware of this, but honestly, nobody 
>> has needed it badly enough yet :) . I kindly ask you to open a pair 
>> of issues on the Github repo. I can't say when we we'll be able to 
>> take a closer look (we're stretched pretty thin right now), but 
>> having open issues helps raise the priority.
>>
>> Case 2, at least, is probably not that hard to implement. Case 1, on 
>> the other hand, is a bit thornier because of the design of the driver.
>> It is focused on doing bulk reads, which are needed to get sufficient 
>> performance with lots of variables. But such reads can only be done 
>> after all the records are initialized and ADS variables made known to 
>> the driver. So, initial readbacks were disabled for simplicity. They 
>> can be added for sure, but it won't be a simple bolt-on.
>>
>> Cheers,
>> Jure
>>
>> On 4/12/24 18:11, Mark Rivers via Tech-talk wrote:
>>> Caution: This email originated from outside of Cosylab.
>>>
>>>
>>> Hi Markus,
>>>
>>> There are 2 separate cases here:
>>>
>>> 1) The PV value getting set to the PLC value during iocInit.
>>> 2) The PV value getting set to the PLC value when the PLC values 
>>> changes after iocInit.
>>>
>>> Case 1 is handled as follows:
>>> - During iocInit the ao record device support (devAsynFloat64.c) 
>>> does a read from the driver to get the current PLC value.  If that 
>>> read operation returns asynSuccess then the PV should be set to the 
>>> PLC value, otherwise it is not changed.  This definitely works fine 
>>> with the Modbus driver, for example.  I am not sure about the 
>>> adsDriver, since I have not used it.  You can add debugging to the 
>>> driver to track that down.
>>>
>>> Case 2 is handled by adding the line you did to database:
>>>       info(asyn:READBACK, "1")
>>>
>>> That should make the ao record value update to match the PLC value 
>>> when the PLC value is changed outside of EPICS.  Note that this line 
>>> is NOT required for getting the behavior described in Case 1 above.
>>>
>>> Mark
>>>
>>>
>>> -----Original Message-----
>>> From: Tech-talk <tech-talk-bounces at aps.anl.gov> On Behalf Of Meyer, 
>>> Markus via Tech-talk
>>> Sent: Friday, April 12, 2024 10:25 AM
>>> To: tech-talk at aps.anl.gov
>>> Subject: Readback of output variables in adsDriver
>>>
>>> Dear all,
>>>
>>> I am evaluating possibilities to communicate with a plc and other 
>>> hardware from beckhoff. I have successfully build the adsDriver [1] 
>>> device support and it seems to work very well for input variables. I 
>>> can also write output variables, but if the value gets changed on 
>>> the plc itself (e.g. by the interlock logic or by another connected
>>> protocol) it is not synced back to the pv. It also seems that the 
>>> current value is not initially read on startup of the IOC.
>>>
>>> For example, this is the pv definition:
>>>
>>> record(ao, "$(P):IC:CB01-SSet") {
>>>       field(DTYP, "asynFloat64")
>>>       field(PREC, "2")
>>>       field(EGU,  "%")
>>>       field(DRVH, "100")
>>>       field(DRVL, "-100")
>>>       field(OUT,  "@asyn($(PORT) 0 0) REAL W P=PLC_TC3
>>> V=HMI.IC.CB01.SSet")
>>>       info(asyn:READBACK, "1")
>>> }
>>>
>>> Before I start the IOC, the plc value is set to 2. If I start the 
>>> IOC, the value of the pv is set to 0. The Timestamp is updated. The 
>>> value in the plc gets not changed. I expected, that the pv value is 
>>> also set to 2. Writing a value to the pv is working as expected.
>>>
>>> Did I miss something here? What can I do to subscribe for changes of 
>>> output variables?
>>>
>>> Thanks,
>>> Markus
>>>
>>> [1]
>>> https://urldefense.us/v3/__https://github.com/Cosylab/adsDriver__;!!
>>> G_ 
>>> uCfscf7eWS!eovU-aYXFfsZIvbTx6Y3tTGma4zwbWLi1xy-LUyW3RghomFH88t9jP45t
>>> oK
>>> nZq8oo1pt5gT5tQhGnPd9QXmCruzGkJg$
>>
>>
>>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System