[Simh] Modem control in TOPS-10

[Jordi Guillaumes i Pons]

Hi everyone,

This one is for the PDP-10/TOPS-10 experts around here. 

A few commits ago, the terminal handling of simh has been fixed so if the multiplexor device (specifically, DZ) is attached with modem control enabled (attach -am DZ <port>), it is not posible to establish a connection into the simulated machine unless the guest operating system enables (and handles) the corresponding modem control lines.

For the VAX simulators running VMS this means you have to $SET TERMINAL/PERM/HANGUP/MODEM TTAx: to be able to TELNET into the simulator. Either this, or attach without “-am” so the lines behave like they are directly connected to the simulated hardware using a null-modem cable.

Why should one use “-am” and care about modem control in a simulated environment? Not considering the case when you want to use a REAL modem (yes, that is supported in simh) and are connecting into the simulator using TELNET, the main reason is if you enable modem control and configure apropriately the guest environment, simh will drop the telnet session when you log off the guest OS (in openvms you have to $LOGOUT/HANGUP, in RSX-11M+ that is the default behaviour of BYE unless you specify /HOLD). Likewise, if you drop manually the telnet connection the OS can kill the process. Whithout modem control that is not posible, and you have to close manually the telnet client.

Previously to the mentioned fix, you could telnet into the simulator and get a connection (and a LOGIN prompt) even if the terminal line in guest OS was not configured for modem control; that was not correct and has been fixed.

I have no problem with VMS or RSX11. I have not yet looked into RSTS. I _have_ looked into TOPS-10, and now I have a problem.

Basically, I don’t know how to enable the modem control lines in the OS side. I have MONGENed the system both confuguring the terminal lines as “dataset” enabled or not dataset enabled, and I’ve got the same result in both cases: can’t get into TOPS-10 if I attach “-am”. I’ve looked into the INITIA parameters but I’ve not been able to find the right incantation to configure properly the terminal lines.

I guess there must be a pretty obvious way to do it, but I’m not able to find it. So… anybody here able to help?

Thanks!

(PS: I’ll move my sights into RSTS soon :))