Re: [TERMINFO BUG?] VT100 reset string ignores scrolling margins and VT52 mode

[Rob King]

Hello,

    I see your point about the "\E<" and "\Ec" reset sequences. I think 
it may still be worthwhile to add "\Er" to the rs2 sequence, though, 
since as you said all of the emulators claiming to be a VT100 at least 
nominally support it.

    Thanks.


On 03/11/2017 04:48 PM, Thomas Dickey wrote:
> On Fri, Mar 10, 2017 at 05:52:02PM -0600, Rob King wrote:
> > Hello,
> >      The class "vt100|vt100-am" terminfo entry has as its rs2
> > sequence "rs2=\E>\E[?3l\E[?4l\E[?5l\E[?7h\E[?8h". This resets all of
> > the various DEC private modes to their default values. This is the
> > only reset string currently defined for the VT100.
> >
> >      This sequence does not appear to reset scrolling margins. As the
> > top and bottom margins are settable via escape sequences, it is
> > possible to get the terminal in a state where scrolling is invalid
> > and not fixable via the reset utility.
> scrolling margins - ok: csr is in the terminal description, and
> there's no existing terminal emulator lacking the feature.
>   
> >      The reset string likewise does not exit out of VT52 emulation
> > mode, which is also something that is settable via software and
> > therefore a place where a user could get "stuck" and beyond the
> > reach of "reset".
> This is more of a problem, since several terminal descriptions
> inherit from vt100 (and like some programs that I don't have
> to mention), most of those didn't bother to implement a workable
> vt52 emulation.  So... resetting vt52 back to vt100 would introduce
> a change that can't be tested.
>   
> >      I would recommend, if possible, updating the reset string to
> > something like "\E<\Ec", which would exit VT52 emulation mode (if
> > the terminal is in such a state) and then use the RIS (Reset to
> > Initial State) sequence to completely reset the terminal state.
> that's harder (no pun intended).  For a real vt100, that would act
> as if you power-cycled the terminal, interrupting the connection.
>
> I keep this in mind:
>
> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=60377
>
> though the particular "rs2" string we're discussing predates ncurses,
> first seen in 4.0BSD, around 1980.
>   
> >      If this is not desirable due to the side-effects of the RIS
> > sequence (which causes the POST to execute), perhaps the existing
> > reset string could be modified to include "\E<\E[r", to get the
> > terminal in ANSI mode and reset its scrolling margins. The "\E<"
> > would need to be the first component of the reset string, since the
> > following components would not be recognized in VT52 mode.
> I'm inclined to incorporate it, but changing the use's for the existing
> stuff to avoid changing old entries.