stty erase '^?' in v7

Noel Chiappa jnc at mercury.lcs.mit.edu
Mon Oct 16 00:39:54 AEST 2017


    > From: Will Senn

    > All that cooked and raw stuff is gobbledegook that I'll have to read up
    > on.

The raw/cooked stuff isn't the source of the worst hair in the TTY driver;
that would be delays (on the output side), and delimiter processing (on the
input side).

The delays are for mechanical terminals, because they need delays after a
motion command (e.g. NL, CR, etc) before the next printing character is sent;
differing for different motion control commands, further complexified by the
current print head position - a Carriage Return from column 70 taking a lot
longer than one from column 10. The driver keeps track of the current column,
so it can calculate this! It does the delays by putting in the output queue a
chacter with the high bit set, and the delay in the low bits; the output start
routine looks for these, and does the delay.

On the input side, every time it sees a delimiter (NL, EOF), it inserts a 0xFF
byte in the input queue, and increments a counter to keep track of how many it
has inserted. I _think_ this is so that any given read call on a 'cooked'
terminal will return at most one line of input (although I don't know why they
don't just parse the buffer contents at read time - although I guess they need
the delimiter count so the read call will wait if there is not a complete line
there yet).

I should look and see how the MIT TTY driver (which also supported 8-bit input
and output) dealt with these...

    Noel


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