USB-RS232 adapters vs. machines w/real consoles.

Following a digression from this post:

http://mail-index.netbsd.org/port-sparc64/2016/11/23/msg002597.html

I decided to investigate my various USB-RS232 adapters.

I have three Prolific pl2303-based adapters, one Belkin/MCT-based adapter
and several KeySpan USA-19HS adapters.

Under Linux Mint 17, the Prolific-based adapters would send BREAK and
the "ok" prompt from OBP (SPARCstation 5-110) would be displayed, but
for some reason, they would not transmit anything else.  (I'll have to
double-check that I have DTR->CD/DSR looped back in my DB9-RJ11 adapters.)

The Belkin/MCT-based adapter did not appear to send/receive anything at
all.  No BREAK, no other keystrokes (again, I'll double-check my DB9-RJ11
adapter).

The KeySpan USA-19HS transmitted BREAK once or twice, but nothing else.
Afterwards, it appeared to lock up and wouldn't transmit anything anymore.
Upon unplugging it, 'cu' terminated and queued keystrokes were delivered
to the shell.

Watching "/var/log/syslog" on the Linux Mint system, it may be that
I'm fighting with its "ModemManager" and it's hijacking my attempts
to transmit anything other than BREAK.

My only other experience with USB-RS232 adapters under penguin-OS is
gNewSense 3 on my Lemote YeeLoong and it's a fairly bare-bones installation
without a "desktop environment".  On it, the KeySpan works flawlessly.
The Linux Mint system is running Xfce.


Under NetBSD/amd64-7.0_STABLE, the Prolific-based devices were fully
functional.  The Belkin/MCT-based device failed to function in the same
manner as under Linux Mint.  The KeySpan devices are not (yet) supported
by NetBSD.

I'm fairly certain the Belkin/MCT adapter worked fine on NetBSD in the
past.  I'm not sure what its issue is now.

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