tty input and output at different speeds?

[guy at sun.UUCP]

> >Obviously I'd have to hack stty(1) and getty to grok split speeds.
> >Are there any other gotchas I should be aware of?
> 
> Yes.  Your hardware has to grok the split speeds too, as well as the
> driver.

Since the system in question is V7-based, the driver presumably handles
split speeds.  If the hardware doesn't support them, it should ignore a
request for split speeds (from the V7 manual: "...If other hardware is used,
impossible speed changes are ignored.").

The 4.3BSD "stty" will not, in general, *set* split speeds (there is an
undocumented "gspeed" option that sets the input speed to 300 baud and the
output speed to 9600 baud), but it will report them properly.  I think this
"stty" is descended from the V7 "stty", so that one may do the same.

The V7 "getty"'s speed tables were compiled into the program, so you'd need
source to hack them.  I believe they were just specified as the five fields
in the "sgttyb" structure, so the input and output speeds were separate and
it wouldn't have to be changed to handle split speeds.

By and large, few other programs set the speed or look at it, so they
wouldn't have to be changed.  "curses" and "vi" look at the output speed to
determine how quickly repainting takes place, so they wouldn't have to be
changed either.
-- 
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy at sun.com (or guy at sun.arpa)