Experimental Physics and
Industrial Control System
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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | Re: StreamDevice, prevent records from getting "stuck" |
| From: | Mark Davis via Tech-talk <tech-talk at aps.anl.gov> |
| To: | tech-talk at aps.anl.gov, "Sobhani, Bayan" <bsobhani at bnl.gov> |
| Date: | Tue, 14 Apr 2020 12:04:40 -0400 |
If the "random characters" tend to occur between normal traffic (i.e. when a device is "driving" the signal lines) or at the end of normal transmissins, that could be an indication that the RS-485 connection is not properly terminated and/or biased. I strongly recommend using digital scope to monitor the voltage levels of the signal wires to see if they are at a sufficient voltage level when nothing is driving the line.
When we where having this sort of problem a couple of years ago with a couple of devices using RS-485 (or RS-422), I read several different how-to's and explanations regarding how RS-485/RS-422 connections work and should be set up. Unfortunately, there is one aspect of these descriptions where people seem to be roughly evenly split: Should have/do you need a common reference for the signal voltages. II suppose this is understandable, since what I read says the original standard said that insuring a "common return path" was optional, but the the newer ANSI/TIA/EIA-485 standard REQUIRES it for proper operation.
In our case, the problem was caused by not having the signal wires sufficiently biased to keep the voltage difference > 200mV when no device is driving them. In our case the Moxas we use for the affected devices include pull up/down resistors that can be enabled and proved sufficient to satisfy this requirement.
If it would be at all helpful, I have some notes I took when learning about all this as well as still pictures and some video of what I found when diagnosing such problems for a couple of the devices at our lab.
Mark Davis
On 4/6/2020 7:48 PM, Sobhani, Bayan via
Tech-talk wrote:
Maybe the reason for the nQueue being 5 is because there are multiple PVs associated with each device.
These are RS-485 temperature controllers that are connected to a moxa. I am not sure if "noise" is the correct word but some of these devices seem to be prone to sending random characters at times. For some of these devices changing the cabling seems to help. Other times it seems to be the device itself.
From: Mark Rivers <rivers at cars.uchicago.edu>
Sent: Monday, April 6, 2020 7:35:29 PM
To: Sobhani, Bayan <bsobhani at bnl.gov>
Cc: tech-talk <tech-talk at aps.anl.gov>
Subject: RE: StreamDevice, prevent records from getting "stuck"Note that asynReport said "nQueued 5". That suggests the port was busy while 5 more I/O requests were queued up.
This looks like a device that is not responding.
Your original message said
`sometimes when the signal is noisy, the PV gets "stuck"`
What do you mean by "signal is noisy". The TCP messages should not be "noisy".
Mark
-----Original Message-----
From: Sobhani, Bayan <bsobhani at bnl.gov>
Sent: Monday, April 6, 2020 5:57 PM
To: Mark Rivers <rivers at cars.uchicago.edu>
Cc: tech-talk <tech-talk at aps.anl.gov>
Subject: RE: StreamDevice, prevent records from getting "stuck"
The command I use to configure the port is drvAsynIPPortConfigure. For some reason I had some trouble reproducing the problems but after a few IOC restarts I got the PVs stuck again.
asynReport 10 PortName gives the following:
c3-tsrv1-p16 multiDevice:No canBlock:Yes autoConnect:Yes
enabled:Yes connected:Yes numberConnects 1
nDevices 0 nQueued 5 blocked:No
asynManagerLock:No synchronousLock:Yes
exceptionActive:No exceptionUsers 1 exceptionNotifys 0
traceMask:0x1 traceIOMask:0x0 traceInfoMask:0x1
interposeInterfaceList
asynOctet pinterface 0x7f3dff3a9a40 drvPvt 0xe99ad0
interfaceList
asynCommon pinterface 0x7f3dff3a6d20 drvPvt 0xe98bc0
asynOctet pinterface 0xe98ca8 drvPvt 0xe98bc0
Port 10.17.2.60:4016: Connected
fd: 5
Characters written: 117
Characters read: 227
After running this, a few seconds later I got the message:
"2020/04/06 18:45:23.072801 c3-tsrv1-p16 XF:17ID-CT{RG:C3}T:1-SP: Timeout after reading 176 bytes "...<ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff><ff>""
And then the PV started reading data again. I am not sure if the asynReport command is somehow fixing this or if it is just a coincidence.
Alex
-----Original Message-----
From: Mark Rivers <rivers at cars.uchicago.edu>
Sent: Monday, April 6, 2020 6:10 PM
To: Sobhani, Bayan <bsobhani at bnl.gov>
Cc: tech-talk <tech-talk at aps.anl.gov>
Subject: Re: StreamDevice, prevent records from getting "stuck"
What asyn driver are you using (drvAsynIPPort, drvAsynSerialPort, etc.)?
You should run the following to see if the problem is in the asyn driver
asynReport 10 PortName
where PortName is the name of the asyn port. That will tell you if the port is connected, etc.
Mark
________________________________
From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Sobhani, Bayan via Tech-talk <tech-talk at aps.anl.gov>
Sent: Monday, April 6, 2020 4:57 PM
To: tech-talk at aps.anl.gov
Subject: StreamDevice, prevent records from getting "stuck"
For StreamDevice I notice that sometimes when the signal is noisy, the PV gets "stuck" if it makes one too many failed requests to the device. Getting "stuck" means that no matter how many times I process the PV with a StreamDevice OUT field, it does not seem to attempt to send anything to the device until I restart the IOC.
I see no technical reason why this must happen so I think this is probably something intentional in StreamDevice. Can I turn this off? I want the PV to always try to send a signal to the device, and if it can't I want to see the red letters saying there was a mismatch.
Is there any way to prevent the PVs from getting "stuck"?
Alex
- Replies:
- Re: StreamDevice, prevent records from getting "stuck" Mark Rivers via Tech-talk
- RE: StreamDevice, prevent records from getting "stuck" Sobhani, Bayan via Tech-talk
- References:
- StreamDevice, prevent records from getting "stuck" Sobhani, Bayan via Tech-talk
- Re: StreamDevice, prevent records from getting "stuck" Mark Rivers via Tech-talk
- RE: StreamDevice, prevent records from getting "stuck" Sobhani, Bayan via Tech-talk
- RE: StreamDevice, prevent records from getting "stuck" Mark Rivers via Tech-talk
- Re: StreamDevice, prevent records from getting "stuck" Sobhani, Bayan via Tech-talk
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