[Simh] going back to the VAX console with CTRL P

[Nelson H. F. Beebe]

List discussions today have commented on the default of Ctl-E (ASCII
005) as the SIMH escape character, to return from a guest O/S to SIMH
itself.

That character is commonly used in the emacs editor family, and in
Unix and TOPS-20 shells, usually to move to end of line.  I was long
ago sufficiently unhappy with the SIMH choice, that I patched local
code before building it with a change like this one:

% diff $S/simh/gnu-linux-ia32/simhv36-0/sim_console.c sim_console.c
92c92
< int32 sim_int_char = 005;                               /* interrupt character */
---
> int32 sim_int_char = 036;                               /* interrupt character */

[From a 2006-vintage diff in my records].

I don't recall whether, at the time, there was any facility for
redefining it in the SIMH startup scripts, avoiding the need to make a
trivial tweak to the SIMH source code.

My 036 choice corresponds to Ctl-^ (caret), a character unused by
either command shells, or the emacs family (although the latter can,
of course, be easily configured or programmed to do so, because their
input model is that EVERY character runs a command, even if most just
insert themselves in the buffer).

The ssh and Kermit intercomputer communications systems both use
two-character escape sequences, because that is an even better choice:
such escapes are rare events, and having to type an extra character is
of neglible human overhead.  Otherwise, keyboard input to the remote
system works much as expected, and all keyboard characters can be
input without interference.

Those of us who run virtual machines on emulation software where the
console is implemented in a Web browser window are continually
impacted by some characters being grabbed by the browser before the VM
console can even see them.  We had similar problems in Denmark, where
THREE essential vowels (Danish has nine such) are missing from the
US-layout keyboards that we then had.

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- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
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