> 
> > The problem is that we only have one output line. Typically it's
> > used to hang up the modem. We need a way to choose which way to
> > go (what to do with the output). The idea is to have crtscts which
> > will, as at present, use the output for hanging up the modem.
> > We'll add cdtrcts to use the output for flow control.
> 
> Hmm... those names seem backwards to me... I don't exactly know what
> crtscts currently does on mac68k though. But anyways, to me, "crtscts"
> says handshake out is used as RTS, handshake in is used as CTS. i.e.
> hardware flow control. "cdtrcts" says handshake out is used as DTR,
> handshake in is used as CTS. i.e. output hangs up modem. And isn't
> crtscts supposed to mean hardware flow control? I think that's what it
> does on the i386 port, and that's what the comment in
> /usr/include/sys/termios.h implies. (The termios(4) manpage says
> something else though... I picked the one that agrees with me ;)
> 
> So, in the current mac68k zs driver, crtscts does _not_ use HSKo for
> flow control?

Yes, but what is HSKo? Is it DTR or RTS? Is it both? Neither? Apple
just didn't consider the case of a modem being able to overload the
computer's ability to receive data. So they figured either DTR or
RTS would be enough.

The names make more sense if you consider the mac serial ports as
not having an RTS output, only DTR. There's precedence for this
as the actual pin in the chip to twiddle for HSKo is the DTR pin.
(RTS is used to enable/disable the transmit buffers.) Also, if you
overrun the buffer on an HP DeskWriter, it complains about a DTR
handshaking overrun. There are also a number of modems, including
mine :-), which use the output as DTR.

crtscts does not, at present, use HSKo for flow control. It does,
however, use CTS for flow control (so we will shut up when asked).

The fact that folks only seem to have trouble when receiving
on BOTH ports indicates that the choice wasn't too bad. We seem to
generally be able to run one port w/o having to ask the other side
(the modem) to hush.

Take care,

Bill