OT: what happens if tcdrain does not come back?

[Andreas Schuldei <andreas@schuldei.org>]

Sorry for the offtopic mail, I do not know any further and I guess someone
here knows something about this:

I configure my ttyS0 (canonical communication, pretty much like out of the
serial programming howto), and write something to it. The other end is
supposed to reply OK, like good modems are supposed to when you talk to them.

But (I think!) I do not even get so far: doing an strace I hang in the
ioctrl(fd, TCSBRK) and it would not return. 

I would have ditched the hardware by now, but the dos demoprogram is running
fine.

Where could be the problem?

And yes, I do see an interrupt.