Re: Modbus Module issue

[Luis Alberto De Sousa Moreira via Tech-talk <tech-talk at aps.anl.gov>]

    Hi Mark,
    
    Bingo!
    All is working now. I can connect and get the correct data.
    
    Thank you all for the help.
    
    Kind Regards
                       Luis

On 25/07/2026 16:35, Mark Rivers wrote:

You should just pull the master branch from GitHub.

Mark

Sent from my iPhone

On Jul 25, 2026, at 9:19 AM, Luis Alberto De Sousa Moreira <luis.moreira at epfl.ch> wrote:

 Hi Mark,
I'm using the latest version from I guess a week ago.
since you pushed the changes to the Master version, shall I just download that and build again or try to modify the version I have?
what is more useful for you?
Kind Regards
               Luis

On 25/07/2026 00:37, Mark Rivers wrote:

Luis,

The Github issue is this line in drvAsynIPPort.c:

https://github.com/epics-modules/asyn/blob/66bafcde239ddc902000e9ec380872c8b621fdf9/asyn/drvAsynSerial/drvAsynIPPort.c#L530

which is this:

            if (connectResult < 0 && ((SOCKERRNO == EWOULDBLOCK) || (SOCKERRNO == EINPROGRESS))) {

This is incorrect, it should not be using EWOULDBLOCK and EINPROGRESS which are OS-dependent.  It should be using SOCK_EWOULDBLOCK and SOCK_EINPROGRESS which are defined in EPICS base and are OS-independent.  This bug was introduced in this commit on May 18, 2026.

https://github.com/epics-modules/asyn/commit/87f952ef8ce2dadf7c156fee2a15c801c6796ae1

What version of asyn are you using?  Is it a master branch more recent than May 18?

I don't understand why this code compiles at all on Windows.  EWOULDBLOCK and EINPROGRESS are used on Linux, MacOS, etc. but should not be defined at all on Windows.  Windows defines WSAEWOULDBLOCK and WSAEINPROGRESS which are functionally equivalent but have different numeric values.  SOCK_EWOULDBLOCK and SOCK_EINPROGRESS are defined as EWOULDBLOCK and EINPROGRESS or WSAEWOULDBLOCK and WSAEINPROGRESS depending on the OS.

I just reproduced the issue on my system with base 7.0.10 and the master branch of asyn.  I am using Visual Studio 2022.   I see this when I try to connect to a known working terminal server:

# This is for Digi SP One

drvAsynIPPortConfigure("serial1", "gsets13:2101", 0, 0, 0)

2026/07/24 17:24:46.862 serial1 -1 autoConnect could not connect: Can't connect to gsets13:2101: Unknown error

I then changed drvAsynIPPort.c to replace EWOULDBLOCK and EINPROGRESS with SOCK_EWOULDBLOCK and SOCK_EINPROGRESS on line 530.  That fixed the problem.

I have pushed the fix to the asyn master branch on Github.

Mark

---

From: Mark Rivers <rivers at cars.uchicago.edu>
Sent: Friday, July 24, 2026 9:43 AM
To: Luis Alberto De Sousa Moreira <luis.moreira at epfl.ch>; tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Modbus Module issue

Hi Luis,

Can you try making the change around line 531 in drvAsynIPPort.c that is described in the Github issue, replacing  EWOULDBLOCK and EINPROGRESS with SOCK_EWOULDBLOCK and SOCK_EINPROGRESS?

Mark

---

From: Luis Alberto De Sousa Moreira <luis.moreira at epfl.ch>
Sent: Friday, July 24, 2026 9:36 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>; Mark Rivers <rivers at cars.uchicago.edu>
Subject: Re: Modbus Module issue

 

Hi Mark,
Just tried everything on your list and the error is the same in all instances.

Kind Regards 
                   Luis

On 24/07/2026 16:24, Luis Alberto De Sousa Moreira via Tech-talk wrote:

Hi Mark,
Will try your suggestions and will let you know the result. The Github issue does seem suspiciously similar.

Thank you.
Kind Regards
              Luis

On 24/07/2026 15:03, Mark Rivers wrote:

Hi Luis,

This does look like there is an issue with drvAsynIPPortConfigure on your machine.  The "Unknown error" message seems strange.  You could try the following:

• Change the IP address from 10.136.0.30 to a non-existent IP address on your subnet.  Does the error message change?
• Change port 502 to a port that won't be supported, like 501.  Does the error message change?
• Switch to an IP address and port of another server that should connect, for example port 80 on a Web server.  Does that connect?  I want to see if drvAsynIPPort is working at all.

Just a few minutes ago someone opened this Github issue

https://github.com/epics-modules/asyn/issues/240

It reports a problem with drvAsynIPPortConfigure() on Windows failing with "Unknown error".  This seems suspiciously similar.

Mark

---

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Luis Alberto De Sousa Moreira via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, July 24, 2026 7:12 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: Modbus Module issue

 

Hi Guys,
I think I tried everything I can think off. Still no connection.
May AI assistant thinks that the issue is that the module was built using MinGW instead of the MSVC tool chain, it is talking about the fact that MinGW uses a "Translation Layer" (POSIX vs. Winsock). I never had any issues before so can't see that being the issue, but wondering what you thoughts are on this.

Kind Regards
                 Luis

On 24/07/2026 10:46, Luis Alberto De Sousa Moreira via Tech-talk wrote:

Hi  Jörn,
I think we getting the wires crossed here... the OPCUA port is 4840 but the 502 port is the normal Modbus port. 
I managed to connect fine to it with other applications in the same machine.

<guqfI6cC6AdYLRNq.png>

Kind Regards
                  Luis

On 24/07/2026 10:38, Jörn Dreyer wrote:

Hi Luis,

are you sure you are using the correct port?
The Beckhoff documentation tells that the OPCUA server is listening on port 4840.  Did you cahnge that when installing the OPCUA Sever on the PLC?
The Ports 500 + x are normally used for the various NC applications in your PLC program.

Regards

Jörn

Am Freitag, 24. Juli 2026, 09:57:38 Mitteleuropäische Sommerzeit schrieb Luis Alberto De Sousa Moreira via Tech-talk:

Just found another application I used before as a Modbus client, called 
EasyModbusClient.
It connects fine and gets data.

This is getting more intriguing...

Best Regards
                   Luis

On 24/07/2026 09:40, Luis Alberto De Sousa Moreira via Tech-talk wrote:

Hi Gabriel,
The firewall seems to be the culprit, but I added rules for the 
application. I also just done a test where I disabled the firewall and 
I get the same result.

D:\FalconDev\EPICS\modbus\iocBoot\iocTest>..\..\bin\windows-x64-mingw\modbusApp.exe 
BPS_Beck.cmd
# BPS_Beck.cmd
# Just testing the modbus module with my BPS Beckhoff PLC.
# 1. Cleanly lock network routing automatically at boot
epicsEnvSet("EPICS_CA_ADDR_LIST", "10.136.0.255")
epicsEnvSet("EPICS_CA_AUTO_ADDR_LIST", "NO")
epicsEnvSet("EPICS_CAS_INTF_ADDR_LIST", "10.136.0.34")
# gvl.mb_Input_Registers[10] := GVL.d_setpoint_T1;              // T1  
                 mS
# gvl.mb_Input_Registers[11] := GVL.d_setpoint_TRamp1;  // Ramp1       
        uS
# gvl.mb_Input_Registers[12] := GVL.d_setpoint_v1;              // V1  
                 10V
# gvl.mb_Input_Registers[13] := GVL.d_setpoint_T2;              // T2  
                 mS
# gvl.mb_Input_Registers[14] := GVL.d_setpoint_TRamp2;  // Ramp2       
        uS
# gvl.mb_Input_Registers[15] := GVL.d_setpoint_V2;              // V2  
                 10V
# gvl.mb_Input_Registers[16] := GVL.d_setpoint_T3;              // T3  
                 mS
# gvl.mb_Input_Registers[17] := GVL.d_setpoint_TRamp3;  // Ramp3       
        uS
# gvl.mb_Input_Registers[18] := GVL.d_setpoint_V3;              // V3  
                 10V
# gvl.mb_Input_Registers[19] := GVL.d_setpoint_pulseLength;     // 
PulseLength  S /mS
# gvl.mb_Input_Registers[20] := GVL.d_setpoint_TRampDown;       // 
RampDown             uS
dbLoadDatabase("../../dbd/modbusApp.dbd")
modbusApp_registerRecordDeviceDriver(pdbbase)
# Get the connection going
drvAsynIPPortConfigure("BPS_Beck", "10.136.0.30:502", 0, 0, 0)
2026/07/24 09:32:59.953 BPS_Beck -1 autoConnect could not connect: 
Can't connect to 10.136.0.30:502: Unknown error
# drvAsynIPPortConfigure("BPS_Beck", "8.8.8.8:8080", 0, 0, 0)
modbusInterposeConfig("BPS_Beck", 0, 5000, 0)
asynSetOption("BPS_Beck",0, "disconnectOnReadTimeout", "Y")
# 
=========================================================================
# Configure Modbus Drivers Memory Blocks
# 
=========================================================================
# Syntax:
# drvModbusAsynConfigure("portName", "tcpPortName", slaveAddress, 
modbusFunction, modbusStartAddress, modbusLength, dataType, pollMsec, 
"plcType")
# drvModbusAsynConfigure("modbusPortName", "asynPortName", 
slaveAddress, modbusFunction, startAddress, length, dataType, 
pollMsec, "plcType")
# Read Coils (Function Code 1)
# Reads 16 binary bits starting at offset 0, polling every 200 
milliseconds.
# drvModbusAsynConfigure("READ_COILS", "PLC_NET", 0, 1, 0, 1, 0, 200, 
"OldPLC")
# Write Coils (Function Code 5)
# Configures a write-only path for coils. pollMsec is 0 because writes 
are instantaneous.
# drvModbusAsynConfigure("WRITE_COILS", "PLC_NET", 0, 5, 0, 1, 0, 0, 
"OldPLC")
# Reads 11 read-only 16-bit registers starting at offset 10, polling 
every 500 milliseconds.
# dataType=0 specifies standard 16-bit unsigned integers (UINT_16).
drvModbusAsynConfigure("READ_INPUTS", "BPS_Beck", 1, 4, 10, 11, 0, 
500, "Beckhoff")
# Read Holding Registers (Function Code 3)
# Reads 1 read/write 16-bit register starting at offset 0, polling 
every 500 milliseconds.
# dataType=0 specifies standard 16-bit unsigned integers (UINT_16).
# drvModbusAsynConfigure("READ_HOLDING", "PLC_NET", 0, 3, 0, 1, 0, 
500, "OldPLC")
# Block E: Write Holding Registers (Function Code 6)
# Configures a write-only path for single registers. pollMsec is 0 for 
on-demand writing.
# drvModbusAsynConfigure("WRITE_HOLDING", "PLC_NET", 0, 6, 0, 1, 0, 0, 
"OldPLC")
# Enable ASYN_TRACEIO_HEX on octet server
# asynSetTraceIOMask("BPS_Beck",0,4)
# Enable ASYN_TRACE_ERROR and ASYN_TRACEIO_DRIVER on octet server
# asynSetTraceMask("BPS_Beck",0,9)
dbLoadRecords("../../db/BPS_Beck.db")
iocInit
Starting iocInit
############################################################################
## EPICS R7.0.10
## Rev. 2026-07-01T08:47+0200
## Rev. Date build date/time:
############################################################################
2026/07/24 09:33:00.992 drvModbusAsyn::doModbusIO port READ_INPUTS 
error calling writeRead, error=asynManager::queueLockPort queueRequest 
failed: port BPS_Beck not connected, nwrite=0/6, nread=0
iocRun: All initialization complete
epics>

Kind Regards
                 Luis



On 23/07/2026 16:24, Gabriel Fedel wrote:

Hi Luis,

Couldn't the firewall be blocking  the EPICS application ?

Best Regards
Gabriel
------------------------------------------------------------------------
*From:* Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Luis 
Alberto De Sousa Moreira via Tech-talk <tech-talk at aps.anl.gov>
*Sent:* Thursday, July 23, 2026 3:59 PM
*To:* Mark Rivers <rivers at cars.uchicago.edu>; tech-talk at aps.anl.gov 
<tech-talk at aps.anl.gov>
*Subject:* Re: Modbus Module issue
Hi Mark,
My other application is using the Modbus protocol, I used it to do the
initial testing on my system.
I tried the telnet command from my MSYS2 environment and it can 
connect...

telnet 10.136.0.30 502
Trying 10.136.0.30...
Connected to 10.136.0.30.
Escape character is '^]'.

Kind Regards
                   Luis

On 23/07/2026 15:31, Mark Rivers wrote:

telnet 10.136.0.30 502

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch

-- 
Luis Moreira
EPFL SB SPC-II, PPH241 (Batiment PPH) Station 13
CH-1015 Lausanne, Switzerland
Tel.    (+41) 21 693 58 37
E-Mail  luis.moreira at epfl.ch