Default “break character” would I think be NUL (^@).  Seems to work that way on my macosx build.  Pressing it three times quickly makes freevt3k prompt me for a command ("Please enter FREEVT3K command (Exit or Continue) :”) which accepts ‘c’ or ‘e’ in a case-insensitive way.  If I choose to continue I find a break has been sent.

And yes, there is a notion of sending a break request message over the VT connection and that is what it does.

My initial itches with freevt3k were about getting it to work with a classic 3000, and it sort of does although it’s kinda iffy for block-mode applications.  I am pretty sure Bruce got at least one thing wrong about the VT protocol (the AM/server should be able to renegotiate its stuff without forcing the TM/client to renegotiate its).  It could stand some modernization; I mean most of the changes I have made to get it to build on macos are the same changes I made to get it to build on FreeBSD and they are pretty much what to do to get it to build with a POSIXy Unix-like OS with BSD-flavored sockets.  Sometimes reading the code is made more difficult by the twisty little maze of platform-specific #ifdefs and I sometimes think about doing some slash-and-burn refactoring that leaves some portability hooks that you go implement for your insufficiently POSIXy or BSD-Socketsy platform (because there will be an implementation for platforms that are sufficiently POSIXy and BSD-Socketsy), in part because a hook that wraps something like send() would be handy for writing tests for the VT implementation.

Then I have another itch, which is to get it to do Telnet so it’ll talk to the SIMH 3000’s simulated ATC.

-Frank McConnell

On Apr 14, 2021, at 13:47, Gavin Scott wrote:
> 
> BREAK is an out-of-band signal. In the original RS-232 it's indicated by (IIRC) holding the serial line at a logic 0 (high level?) for the duration of an entire character (or something like that) so it's not possible to emulate it transmitting some sequence of characters.  In VT3K, it's probably either a special VT message packet or some bit set in a message, so the freevt3k would have to look for some character typed by the user and then send the appropriate command to the hose via the VT3K protocol. It may well do this and none of us know or remember how to trigger it 😊
> 
> In telnet, it uses something like CTRL-] to bring up a telnet> prompt from which you can do things like "send brk" to trigger the same kind of functionality in the telnet protocol.
> 
> Looking at some freevt3k source code on GitHub, it looks like you can invoke it with -C breakchar to specify what break character you want to use. It's not clear to me if there's a default value for that or not. Also if you press that character three times in a one second period it should drop into a freevt3k command mode similar to what telnet> provides. But pressing it once should get it to send a BREAK command to the host.
> 
> G.
> 
> -----Original Message-----
> From: HP-3000 Systems Discussion <[log in to unmask]> On Behalf Of James B. Byrne
> Sent: Wednesday, April 14, 2021 3:28 PM
> To: [log in to unmask]
> Subject: Re: [HP3000-L] [EXT]: How to stop PING on HP3000
> 
> 
> 
> 
> 
> On Wed, April 14, 2021 16:09, Ralph Bagen wrote:
>> Suggestion was to perform an ABORTJOB #Sxxxx or do an ABORTIO on the 
>> LDEV for
> either the printer or the ping session...
>> 
>> 
> 
> I ended up logging on a different session and aborting the session with the uninterruptible ping.
> 
> There does not seem to be any way to emulate an HP BREAK, which apparently is different from other type of BREAK, many of which differ from one another.
> 
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