[Simh] VAX DZ terminal controller unit?

[Gary Lee Phillips]

Thanks, Mark. I was planning to try the VH emulation this weekend, in
fact. I'd held off because I wasn't sure I could use a Qbus device
with the Microvax emulator, and thought I might have to build the
11/780 emulation instead.

I have more information on the DZ, too. After much blind and random
experimenting, I found that using this command on the VAX side will
make the TTAx ports behave in a somewhat more predictable manner:

SET TERM TTAx -
  /MODEM -
  /DIALUP -
  /HANGUP -
  /DISCONNECT -
  /NOAUTOBAUD -
  /PERMANENT

Note that these settings go away when the VAX is rebooted, so they
probably should be added to SYSTARTUP_VMS.COM or some other script
that will reset them after a boot.

By setting those flags for each of the ports on the DZ, I get a
consistent result. The telnet session is completely disconnected on
logout, closing the telnet window, and no _TTAx process is left
hanging around on the VAX side. The remaining issue is some slowness
in getting up a prompt when first connecting, and that may be related
to what you've described here. I find that it takes 20 to 30 seconds
for the login prompt to appear after pressing the ENTER key, but after
that everything works well.

I'll give the VH a try, possibly today.

--Gary

On Sat, May 21, 2011 at 8:40 AM, Mark Pizzolato - Info Comm
<Mark at infocomm.com> wrote:
> Hi Gary,
>
> The strange behavior with the delays is due to the "_TTAx" processes
> which are running.  I recall seeing these types of issues when we
> connected real VAX terminal ports to each other (for purposed of serial
> networking and/or simple Kermit or other access with there weren't
> working network connections).  The "_TTAx:" processes where created when
> one side started sending something and a login process got started.  We
> called the phenomena the "Who-Huh" problem.  Each computer was sending a
> "Username" prompt (aka "who") at each other and ultimately the other
> system didn't recognize the "Username:" prompt as a username on its
> system so it rejected the login attempt (aka "Huh").
>
> In any case, this certainly shouldn't be happening on DZ ports.  I am
> exploring the precise cause in the DZ emulation and will eventually have
> a fix.
>
> Meanwhile, the absolutely easiest "work around" to achieve your goal of
> host to VAX login access is to use DH Ports instead of DZ ports.  The DH
> emulation does not have this bug.  This would be achieved by:
>   sim> set vh enable
>   sim> attach vh 8501
>
> - Mark Pizzolato
>