[TUHS] Line Terminators in Text Files [Was: Re: Why Pascal is Not My Favorite Programming Language - Unearthed!]

Noel Chiappa jnc at mercury.lcs.mit.edu
Tue Sep 5 08:44:07 AEST 2017


    > From: Chris Torek

    > termcap has entries for the number of NUL characters to insert after
    > carriage return.

Actually, the stock terminal driver in V6 Unix (here:

  http://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/sys/dmr/tty.c

if anyone wants to see the actual code; it's in ttyoutput()) had some pretty
complex code to do just the right amount of delay (in clock ticks) for a large
number of different motion contral characters (TAB, etc, in addition to LF and
CR), and then uses the system timer to delay that amount of real time after
sending such a character (see the very bottom of ttstart()).

E.g. for a NL, it used the fact that it 'knew' which column the print head was
in to calculate the exact return time.

Clever, but alas, it did this by sticking 'characters' in the buffered output
stream with the high bit set, and the delay required in the low 0177 bits,
which the output start routine interpreted; as the code drolly notes, "thus
(unfortunately) restricting the transmission path to 7 bits". Which was a real
PITA recently when I tried to download a binary file to an LSI-11 from a V6
running in Ersatz-11! I had to tweak the TTY driver to allow 8-bit output...

   Noel


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