[Vm-dev] RE: Serial ports on Linux

Schwab,Wilhelm K bschwab at anest.ufl.edu
Wed Sep 1 19:36:57 UTC 2010


If you have some experience with serial I/O on Linux, I would appreciate your giving it a quick shakedown; if it is just plain broken or is still known to work, it would be nice to confirm either way.  I would like to use the binary distribution, but it does not report enough of what it is trying to do (so no clues when things fail) and I end up hacking to add tracing with possible installation troubles as a result.

That said, this time around, I find myself in serialPortOpenByName() and puzzled by the failure being allegedly detected by:

    /* save the old state */
    if (tcgetattr(sp->spDescriptor, &sp->spTermios))

My question: is there old state to save on the first pass?  errno is not helpful; it is set to 5 aka I/O error :(   I find myself wondering whether this should be conditional on the internal state of the descriptor, and the failure to open simply being that it gives up too easily?  Then again, it could be detecting a true error condition and preventing certain disaster in the lines that would follow.

Any ideas?  I can't get /dev/ttyS0 to open by name or number.  'COM1' worked nicely on Windows.


Markus Lampert markuslampert at yahoo.com
Wed Sep 1 15:28:38 UTC 2010

Hi Bill,

haven't used the serial interface with the new VMs (yet), but previously under 
Linux I had to use the vm option '-notimer'. I did not find any negative side 
effects with that option.

Hope this helps,

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