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NeuronRobotics / nrjavaserial

A Java Serial Port system. This is a fork of the RXTX project that uses in jar loading of the native code.
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HUPCL is unconditionally cleared in configure_port #153

Closed a3f closed 4 years ago

a3f commented 4 years ago

The Linux default is that new ports have the HUPCL flag (hang up) set, so RTS is released when the last user of the port closes the device file. rxtx always reconfigures new ports with

ttyset.c_cflag = CREAD | CS8 | CLOCAL;

which overrides the HUPCL flag. Here is an example how this breaks HW that expects RTS to be inactive when the serial port is unused: https://forum.arduino.cc/index.php?topic=46144.0

I've a similar setup where a modem expects RTS to be deasserted when the host doesn't communicate with it. This needs to work even if the application terminates abnormally, so I use the same fix locally, but would like to have the functionality upstream as well.

As I guess there might be *nix systems where HUPCL is not a default, I could draft a patch that doesn't remove HUPCL if it's already set for a port. This would still break setups, where the user runs rxtx, sets RTS to active, close the application and expects the RTS to stay asserted. I don't know how common such a use case is though.

Thoughts?

Note: I am not using your fork, but from a cursory look that part of the code is identical. So I figured I should ask for feedback on the approach here as well, as it seems to be the most active fork.

madhephaestus commented 4 years ago

can you make it configurable so the default behavior is the same as the legacy, but adding this functionality as a user setting?

a3f commented 4 years ago

That would work too. Do you have an example of an existing user setting that could be taken as a template?

a3f commented 4 years ago

I'll close this issue for now. Should we implement the user setting on top of this fork, I'll open a pull request.

Cheers,