[Simh] HP Terminal emulators, MSKermit with DosBox, CKermit 9 to the HP3000

[Clem Cole]

On Tue, Apr 12, 2016 at 5:41 PM, Rodney Brown <rdbrown at pacific.net.au>
wrote:

> None of the terminal emulators could send a BREAK under DosBox. I think
> that a BREAK needs to be synthesized, so DosBox
> recognizing the UART behavior and converting it into a Telnet Break
> command (RFC 854 (IAC, BRK == bytes 255, 243)) may be
> challenging. Adding a DosBox keyboard command to send a Break when
> connected by Telnet should be easy.
>

​Hang on -- BREAK is not in the old USASCII ​7 bit map.   As explained in
RFC 854, it was a >>key<< on the old Teletype ASR33 (and the ATTEN key on
the IBM 2741).   What BREAK did was sent a very long (i.e. 1 second if I
remember correctly) "marking" time signal.  Most UARTS were set up to
recognize this as an "out of band" signal tell the OS to do something
special.

You are correct that a number of OS, would use a >>combination<< of BREAK
followed by some defined pattern to try to auto-detect the speed.
Sometimes when in auto detect, you just send t break repeatedly until what
was being displayed on the screen matched something valid.

Anyway the problem is how to >>send<< a BREAK if its not a special key.
The standard way this has been handled it drop the BAUD rate to be as slow
as possible (50 baud) and send an ASCII @      Assuming 50 baud is not
being used, then it will look like a BREAK to the UART on the other side.
[Open up the code for UUCP's uucico program if you want an example of how
this done -- Warren has the sources to V7 UNIX on his site]




One other question/thought.  I can not speak for DOSBOX, but I know VMware
does supports sending a BREAK.   It will send a break from the host
keyboard to the VM using the GUI.   That said, I know the issue you are
caught with is you want the application AdvanceLink/Kermit et al, to send a
BREAK down the virtual serial line (telnet).  The question is what does DOS
with the BREAK when it gets it (I'm not he road so I can not look at my
handy of the MSDOS encyclopedia).   Assume DOS does not "eat" the BREAK but
some how passes it to the application, then I think the pieces are there
for the application.



Clem
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