[Xastir] Serial port issues with Xastir on OS X

[Alex Carver]

--- On Thu, 8/19/10, Curt, WE7U <curt.we7u@> wrote:

> 
> > Ah!  Changing the device to
> /dev/cu.PL2303-######## made Xastir much happier. I'm not
> sure exactly what goes wrong when I configure Xastir to use
> the other device, but the latter works fine with regular
> terminal applications.  As per the second part of my
> previous reply, I'm guessing Xastir still fails to
> read/write the serial port lock file, but apparently it
> doesn't affect operation.
> 
> Since several people have happily run on OSX for a while I
> was
> wondering about that part of it myself.
> 
> The /dev/cu* vs. /dev/tty* thing reminds me of WAY back on
> Linux
> when we kept having to change what device to talk to for
> terminals
> and modems 'cuz the kernel driver folks kept changing their
> minds.
> I remember using /dev/tty*, then going to /dev/cu*, then
> back to
> /dev/tty*.
> 
> Glad you got it working!
> 

The difference between cu and tty goes into the hardware handshaking.  Any of the cu devices ignores hardware handshake while the tty side needs it.  The idea was that you could open a modem on cu even if the modem says it's not ready and ensure you could control it even if it was in a confused state.  The tty port would honor the handshake/control lines so if the lines weren't asserted properly you weren't going to talk to the device at all.

It wouldn't surprise me if the end result of this mess was that opening the tty got hung up because the USB adapter didn't fully implement handshaking and therefore the driver sees a busy device.  Opening cu bypasses that and it works even if the port is "busy".

It's also interesting that OS X has tty and cu because Linux kernels deprecated cu in version 2.2 (but still there and working last I noticed) .