BusConductor without any module

[M256-Automation]

This is a recap of the problem discussed in the PLCnext Communuty Forum

busconductor-without-any-module

I have a project in which I can choose the file config.txt to place in /opt/plcnext/projects/BusConductor.
The selection is made in eHMI, so the user can select the local configuration during the startup of the plant.
I have 20 different configurations and everything works perfectly.
Now I have to define a configuration with no module, so I made a config.txt with just a "0" inside.
But the configuration doesn't seem to work. This is what I get in the Output.log:

27.04.20 06:51:01.245 BusConductor.BcComponent INFO - Resetting local I/O driver...
 27.04.20 06:51:01.274 BusConductor.BcComponent INFO - Done resetting driver.
 27.04.20 06:51:01.274 BusConductor.BcComponent INFO - Creating local I/O configuration...
 27.04.20 06:51:01.315 BusConductor.BcComponent INFO - Done creating configuration.
 27.04.20 06:51:01.316 BusConductor.BcComponent INFO - Reading local I/O configuration...
 27.04.20 06:51:01.322 BusConductor.BcComponent INFO - Done reading local I/O configuration.
 27.04.20 06:51:01.322 BusConductor.BcComponent ERROR - Read local I/O configuration failed. Response message too short.

Looking at the code I see the cause of exclusion (that comes before the file reading):

// Get the number of I/O modules detected
  // TODO: Check the "More Follows" word (receiveData[3]), and handle the situation where
  // there are more I/O modules than can fit in one message.
  if (receiveData.size() < 8)
  {
  this->log.Error("Read local I/O configuration failed. Response message too short.");
  return false;
  }

  num_modules = receiveData[7];

I tried commenting out just the "return false;" and leaving there the error message, and it worked, even if the LED D is flashing:

    27.04.20 08:09:07.732 BusConductor.BcComponent INFO - Resetting local I/O driver...
    27.04.20 08:09:07.784 BusConductor.BcComponent INFO - Done resetting driver.
    27.04.20 08:09:07.784 BusConductor.BcComponent INFO - Creating local I/O configuration...
    27.04.20 08:09:07.826 BusConductor.BcComponent INFO - Done creating configuration.
    27.04.20 08:09:07.826 BusConductor.BcComponent INFO - Reading local I/O configuration...
    27.04.20 08:09:07.829 BusConductor.BcComponent INFO - Done reading local I/O configuration.
    27.04.20 08:09:07.830 BusConductor.BcComponent ERROR - Read local I/O configuration failed. Response message too short.
    27.04.20 08:09:08.831 BusConductor.BcComponent INFO - Loading local I/O process data mapping...
    27.04.20 08:09:08.835 BusConductor.BcComponent INFO - Done loading process data mapping.
    27.04.20 08:09:08.835 BusConductor.BcComponent INFO - Enabling I/O data output...
    27.04.20 08:09:08.839 BusConductor.BcComponent INFO - Done enabling data output.

As suggested, instead of changing the code, i just bypassed the BusConductor procedure for this specific configuration, leaving a not running local bus.

It works but generates a red flashing LED D.

Thanks

[martinboers]

I've investigated this and the solution is to stop the Axioline setup routine immediately after the "Reset" command is sent, in cases where no I/O modules are expected.

This means that the config.txt file needs to be checked at an earlier point in the startup process. There are at least two possibilities for detecting an empty user configuration:

1. If the config.txt file contains a single line containing the number "0", representing the total number of expected I/O modules.

2. If the config.txt file is missing altogether.

The second of these is probably the quickest fix, since we only need to add a check for the presence of the config.txt file, rather than the contents of the file.

How does this sound?

[M256-Automation]

Hello Martin,
considering the way I use BusConductor (I have all different config.txt files in a user folder and then I copy and paste the chosen one in the defined path) I would prefer to have a file with a "0" inside.
It would also let the user detect a missing config.txt file.

Thanks for your never ending help!

[martinboers]

I have now pushed a feature branch. I only have PLCs with FW version 2021.0, and I would prefer not to downgrade them to an earlier FW version, so because of #3 I have not tested these changes.

I will test & merge the changes when FW version 2021.3 is available, probably in March, unless someone else tests the changes first.

[martinboers]

Tested OK with FW 2021.6.