[TUHS] Compatibility question

Warner Losh imp at bsdimp.com
Mon Dec 18 04:59:52 AEST 2023

On Sun, Dec 17, 2023 at 11:48 AM Paul Winalski <paul.winalski at gmail.com>

> One problem that the VT100 emulators may have is that they behave
> according to the published VT100 specifications rather than the actual
> hardware behavior.

They behave like the author of the emulator thinks the documentation
But often, ambiguity in descriptions lead to bad decisions here,
especially when
you go to the far right of the screen, the bottom right corner, etc.
There's several
quirks of VT100 behavior that just aren't clearly documented. They aren't
per se, but people depend on that behavior.

> The VT100 had notoriously buggy firmware.  Alan Kotok, one of DEC's
> early engineers, encountered some of these and was annoyed enough
> about it that he wrote a program to generate a complete list of escape
> sequences--legal and illegal--which he fed to his VT100 terminal.  The
> results were highly entertaining.  Some perfectly valid escape
> sequences were mishandled by the firmware and had behavior that didn't
> match the documentation.  Even worse, some illegal escape sequences
> caused catastrophic behavior, such as the terminal freezing with the
> alarm continuously on--the only way out was to power-cycle the
> terminal.  One particularly nasty escape sequence caused corruption of
> the EPROM such that the terminal crashed on power-up or restart,
> resulting in an infinite crash-and-restart loop that could only be
> fixed by sending the terminal in for a factory reset.
> Kotok published his results within DEC engineering and shortly
> thereafter "email bombs" containing escape sequences that triggered
> some of the milder of the bugs started circulating.  The VAX/VMS mail
> utility had to be changed to filter out escape sequences by default.

Yea... Those are fun...  I wonder how many got fixed in later versions?

I'd also read somewhere that VT220 development was slowed by
having to behave exactly the same way as the VT100s (the above
example was one given)...  But at least they had the benefit of being
able to look at the old firmware code... At least I'd suppose that was
a benefit...

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