linux-kernel - RE: should RTS init in serial core be tied to CRTSCTS

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Date:	Thu, 8 Mar 2007 19:43:15 +0100
From:	"Tosoni" <jp.tosoni@...sys.fr>
To:	"'Krzysztof Halasa'" <khc@...waw.pl>,
	"'Carl-Daniel Hailfinger'" <c-d.hailfinger.devel.2006@....net>
Cc:	"'Robin Getz'" <rgetz@...ckfin.uclinux.org>,
	"'Oleksiy Kebkal'" <kebkal@...il.com>,
	"'Mike Frysinger'" <vapier.adi@...il.com>,
	"'Linux Kernel Mailing List'" <linux-kernel@...r.kernel.org>,
	<linux-serial@...r.kernel.org>
Subject: RE: should RTS init in serial core be tied to CRTSCTS

Krzysztof Halasa wrote:

> OTOH I wonder what does the device in question require WRT the
> serial port and WRT RTS line in particular.
> I know there are some half-duplex converters which drive RTS only
> while sending and which require CTS to send.

As far as I know in the old times this was the *standard* way to use a modem
(per CCITT V24), and even nowadays many modems can handle this method for
transmit, to stay compatible with the standard.

Think of radio modems. Some are inherently half duplex.

> They are perhaps a bit broken <snip>
No, no, they apply an old standard. Probably they are old as well.
>
> I don't know if one can expect RTS to stay low all the time. Even
> a simple /sbin/setserial from /etc/rc.* would drive it high for
> a moment. I'm afraid the only way which makes sense may be using
> a customized plug.

It's a pity that Linux (or Unixes) never handled RTS this way.
I feel that the /proc or sysfs solutions are the best to alter this well
established default in this driver. It would not break existing installed
hardware.

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