4 Sep
2017
4 Sep
'17
5:33 p.m.
Time delay for physical movement of the print head is
the main
reason that termcap has entries for the number of NUL characters
to insert after carriage return.
This is not quite right. For instance, there are delay values for
line and character insert and delete operations, which were
required back when terminals were slow and bit rates were inching
up ("stty 19200" finally going in as a name for EXTA, one of the
two externally-controlled bit rates in the old drivers...).
(The 4BSD tty driver had CR/LF delays built in, too, no doubt
inherited from 32V. It had to be done in the tty driver, not in
termcap, since command line utilities mostly did not use termcap
in the first place.)
As for termcap delays: some of the software on those terminals was
particularly bad. The Heathkit H19, for instance, implemented the
repeat-counted line and character insert and delete ANSI escape
sequences ESC [ %d <code> with a loop that inserted or deleted one
line or character, N times. (I had an H19, and kept it in this
mode instead of the other one that did not have the N-character
ops -- even with the required delays, if you got the editor to use
them, they were much faster over slow modems.)
(I hacked on the Gosling Emacs display driver quite a bit to tune
it up for our displays, including the Ann Arbor Ambassador displays
that did up to 60 lines in Squint Mode.)
Chris