Experimental Physics and
Industrial Control System

Hi Paul,

 

I was able to do some tests today.  The first device I tested was a Koyo Direct Logic 205 PLC.  I tested disconnecting the Ethernet cable for 1 minute and for 30 minutes.  I repeated each test 3 times.

 

This is the important part of the startup script.  Note that I enabled “disconnectOnReadTimeout”.  There are 5 Modbus drivers doing input operations and polling the PLC at 10 Hz.

 

drvAsynIPPortConfigure("Koyo","10.54.160.50:502",0,0,0)

asynSetOption("Koyo",0, "disconnectOnReadTimeout", "Y")

modbusInterposeConfig("Koyo",0,0)

 

# NOTE: We use octal numbers for the start address and length (leading zeros)

#       to be consistent with the PLC nomenclature.  This is optional, decimal

#       numbers (no leading zero) or hex numbers can also be used.

 

# The DL205 has bit access to the Xn inputs at Modbus offset 4000 (octal)

# Read 32 bits (X0-X37).  Function code=2.

drvModbusAsynConfigure("K1_Xn_Bit",      "Koyo", 0, 2,  04000, 040,   "UINT16",  100, "Koyo")

 

# The DL205 has bit access to the Xn words at Modbus offset 40400 (octal)

# Access the same 32 bits (X0-X37) as word inputs.  Function code=4.

drvModbusAsynConfigure("K1_Xn_In_Word",  "Koyo", 0, 4,  040400, 02,   "UINT16",  100, "Koyo")

 

# The DL205 has bit access to the Yn outputs at Modbus offset 4000 (octal)

# Read 32 bits (Y0-Y37).  Function code=1.

drvModbusAsynConfigure("K1_Yn_In_Bit",   "Koyo", 0, 1,  04000, 040,   "UINT16",  100, "Koyo")

 

# The DL205 has bit access to the Yn outputs at Modbus offset 4000 (octal)

# Write 32 bits (Y0-Y37).  Function code=5.

drvModbusAsynConfigure("K1_Yn_Out_Bit",  "Koyo", 0, 5,  04000, 040,   "UINT16",    1, "Koyo")

 

# The DL205 has bit access to the Cn bits at Modbus offset 6000 (octal)

# Access 256 bits (C0-C377) as inputs.  Function code=1.

drvModbusAsynConfigure("K1_Cn_In_Bit",   "Koyo", 0, 1,  06000, 0400,  "UINT16",  100, "Koyo")

 

# Access the same 256 bits (C0-C377) as outputs.  Function code=5.

drvModbusAsynConfigure("K1_Cn_Out_Bit",  "Koyo", 0, 5,  06000, 0400,  "UINT16",    1, "Koyo")

 

# The DL205 has bit access to the Cn words at Modbus offset 40600 (octal)

# Access 256 bits (C0-C377) as inputs.  Function code=3.

drvModbusAsynConfigure("K1_Cn_In_Word",   "Koyo", 0, 3,  040600, 020, "UINT16",  100, "Koyo")

 

# Access the same 256 bits (C0-C377) as outputs.  Function code=6.

drvModbusAsynConfigure("K1_Cn_Out_Word",  "Koyo", 0, 6,  040600, 020, "UINT16",    1, "Koyo")

 

The first disconnect was at 11:33:01.  There are 2 messages from each Modbus driver.  The first error is read or timeout, and the second is a queueRequest failure because the underlying port has disconnected after the timeout.

 

2023/11/20 11:33:01.754 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 11:33:01.810 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

2023/11/20 11:33:01.830 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

2023/11/20 11:33:01.838 drvModbusAsyn::doModbusIO port K1_Xn_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

2023/11/20 11:33:01.847 drvModbusAsyn::doModbusIO port K1_Xn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

2023/11/20 11:33:01.854 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port Koyo not connected, nwrite=0/6, nread=0

2023/11/20 11:33:01.910 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port Koyo not connected, nwrite=0/6, nread=0

2023/11/20 11:33:01.930 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port Koyo not connected, nwrite=0/6, nread=0

2023/11/20 11:33:01.938 drvModbusAsyn::doModbusIO port K1_Xn_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port Koyo not connected, nwrite=0/6, nread=0

2023/11/20 11:33:01.947 drvModbusAsyn::doModbusIO port K1_Xn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest failed: port Koyo not connected, nwrite=0/6, nread=0

 

I reconnected the cable at about 1 minute later at 11:34:01. It took an additional 85 seconds before the driver recovered.

 

2023/11/20 11:35:17.276 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit writeRead status back to normal having had 125 errors, nwrite=6/6, nread=6

2023/11/20 11:35:17.338 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit writeRead status back to normal having had 125 errors, nwrite=6/6, nread=34

2023/11/20 11:35:17.361 drvModbusAsyn::doModbusIO port K1_Cn_In_Word writeRead status back to normal having had 125 errors, nwrite=6/6, nread=34

2023/11/20 11:35:17.369 drvModbusAsyn::doModbusIO port K1_Xn_Bit writeRead status back to normal having had 125 errors, nwrite=6/6, nread=6

2023/11/20 11:35:17.377 drvModbusAsyn::doModbusIO port K1_Xn_In_Word writeRead status back to normal having had 125 errors, nwrite=6/6, nread=6

 

This is the second time I disconnected for 60 seconds.  For brevity I only show the first 2 error messages.

 

2023/11/20 11:36:13.646 drvModbusAsyn::doModbusIO port K1_Xn_In_Word error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 11:36:13.647 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

 

I reconnected the cable at about 60 seconds later at 11:37:13. It took about another 70 seconds before the driver recovered.

 

2023/11/20 11:38:22.565 drvModbusAsyn::doModbusIO port K1_Xn_In_Word writeRead status back to normal having had 119 errors, nwrite=6/6, nread=6

2023/11/20 11:38:22.573 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit writeRead status back to normal having had 119 errors, nwrite=6/6, nread=6

 

This is the third time I disconnected the cable for 60 seconds.

 

2023/11/20 11:38:53.778 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 11:38:53.785 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

 

I reconnected the cable about 60 seconds later at 11:39:55.  This time the driver recovered within about 6 seconds.

 

2023/11/20 11:40:01.096 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit writeRead status back to normal having had 63 errors, nwrite=6/6, nread=34

2023/11/20 11:40:01.110 drvModbusAsyn::doModbusIO port K1_Cn_In_Word writeRead status back to normal having had 63 errors, nwrite=6/6, nread=34

2023/11/20 11:40:01.118 drvModbusAsyn::doModbusIO port K1_Xn_Bit writeRead status back to normal having had 63 errors, nwrite=6/6, nread=6

2023/11/20 11:40:01.126 drvModbusAsyn::doModbusIO port K1_Xn_In_Word writeRead status back to normal having had 63 errors, nwrite=6/6, nread=6

2023/11/20 11:40:01.134 drvModbusAsyn::doModbusIO port K1_Yn_In_Bit writeRead status back to normal having had 63 errors, nwrite=6/6, nread=6

 

I then did 3 tests where I left the cable disconnected for 30 minutes.

 

This is the first test with 30 minute disconnect.

 

2023/11/20 11:41:08.070 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 11:41:08.077 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

2023/11/20 11:45:27.934 Koyo -1 autoConnect could not connect: Can't connect to 10.54.160.50:502: Connection timed out

 

I reconnected the cable after a little over 30 minutes.  The driver recovered in less than a minute.

 

2023/11/20 12:14:29.424 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit writeRead status back to normal having had 1821 errors, nwrite=6/6, nread=34

2023/11/20 12:14:29.438 drvModbusAsyn::doModbusIO port K1_Cn_In_Word writeRead status back to normal having had 1821 errors, nwrite=6/6, nread=34

 

This is the second test with 30 minute disconnection.

 

2023/11/20 12:15:06.041 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 12:15:06.048 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

 

The cable was reconnected about 12:45:06 and the driver recovered in a few seconds.

 

[Mon Nov 20 12:45:23 2023] 2023/11/20 12:45:23.675 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit writeRead status back to normal having had 1654 errors, nwrite=6/6, nread=34

[Mon Nov 20 12:45:23 2023] 2023/11/20 12:45:23.689 drvModbusAsyn::doModbusIO port K1_Cn_In_Word writeRead status back to normal having had 1654 errors, nwrite=6/6, nread=34

 

This is the third test with 30 minute disconnection.

 

2023/11/20 12:45:53.567 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit error calling writeRead, error=10.54.160.50:502 read error: Resource temporarily unavailable, nwrite=6/6, nread=0

2023/11/20 12:45:53.580 drvModbusAsyn::doModbusIO port K1_Cn_In_Word error calling writeRead, error=asynManager::queueLockPort queueRequest timed out, nwrite=0/6, nread=0

 

The driver recovered in less than a minute after reconnecting the cable.

 

2023/11/20 13:16:12.295 drvModbusAsyn::doModbusIO port K1_Cn_In_Bit writeRead status back to normal having had 1655 errors, nwrite=6/6, nread=34

2023/11/20 13:16:12.308 drvModbusAsyn::doModbusIO port K1_Cn_In_Word writeRead status back to normal having had 1655 errors, nwrite=6/6, nread=34

 

I also tested with a LabJack-T8 analog and digital I/O device.

 

I observed very similar behavior to the Koyo PLC in most cases.  It reconnected OK whether the disconnection was 1 minute or 30 minutes.  However, in 2 cases it would never reconnect.

When this happened I observed the following:

• Attempting a manual telnet from Linux to port 502 (Modbus port) just hung.  It did not give either a connection message or a connection refused message.  I waited several minutes and saw no response.
• Restarting the IOC did not work, it could not connect to the device.
• Only power-cycling the device fixed the problem.
• I think this indicated that the device has a bug, and that sometimes disconnecting the Ethernet cable leaves it in an unusable state. 

 

I conclude that the EPICS Modbus driver appears to be behaving correctly when the network cable is disconnected for either 1 minute or 30 minutes, since it behaves fine with the Koyo PLC.  It does fail sometimes with the Labjack device, but that is clearly a problem with the LabJack, since it requires a power-cycle to fix.

 

Your PLC may also have issues with the network stack when the Ethernet cable is disconnected, and hence the connection is not cleanly closed.

 

Mark

 

 

 

Hi Mark,

Yes, this issue is caused by disconnecting the network cable at the PLC end, so the connection is not closed cleanly. Asyn.CNCT reports Disconnect, just once, the moment the cable is removed.

If I leave it disconnected for roughly up to a minute, the connection is always re-established and asyn.CNCT reports Connect, just once, as expected.

The problem only seems to occur when I leave the cable disconnected for longer, usually 5 mins or more. Sometimes upon re-connection it works Ok, but more often than not on re-connection the asyn.CNCT status repeatedly flips between Connect and Disconnect. Looking at the socket (using netstat -at) for the PLC port it reports CLOSE_WAIT, interspersed with ESTABLISHED.

I’m currently using asyn4-38 and modbus-R2-4. One of the first things I tried was using more up to date versions, so I downloaded asyn-R4-43 and modbus-R2-11, but the problem still occurred.

 

Regards

Paul

 

 

 

If I understand correctly this happens when you disconnect the cable. So the PLC has not cleanly closed the connection, correct?