Some devices take undesired actions when RTS and DTR are

asserted. Some development boards for example will reset on DTR,
and some radio interfaces will transmit on RTS.

This patch allows "stty -f /dev/ttyu9.init -rtsdtr" to prevent
RTS and DTR from being asserted on open(), allowing these devices
to be used without problems.

Reviewed by:    imp
Differential Revision:  https://reviews.freebsd.org/D20031

3 files changed, 10 insertions, 0 deletions

diff --git a/bin/stty/modes.c b/bin/stty/modes.c
index e34afb83ee38..0fe4e5168d2c 100644
--- a/bin/stty/modes.c
+++ b/bin/stty/modes.c
@@ -91,6 +91,8 @@ static const struct modes cmodes[] = {
 	{ "-rtsflow",	0, CRTS_IFLOW },
 	{ "mdmbuf",	MDMBUF, 0 },
 	{ "-mdmbuf",	0, MDMBUF },
+	{ "rtsdtr",	0, CNO_RTSDTR },
+	{ "-rtsdtr",	CNO_RTSDTR, 0 },
 	{ NULL,		0, 0 },
 };
 
diff --git a/bin/stty/print.c b/bin/stty/print.c
index 03d5c3b8a770..a76cd46b765e 100644
--- a/bin/stty/print.c
+++ b/bin/stty/print.c
@@ -184,6 +184,12 @@ print(struct termios *tp, struct winsize *wp, int ldisc, enum FMT fmt)
 	put("-dsrflow", CDSR_OFLOW, 0);
 	put("-dtrflow", CDTR_IFLOW, 0);
 	put("-mdmbuf", MDMBUF, 0);	/* XXX mdmbuf ==  dtrflow */
+	if (on(CNO_RTSDTR))
+		bput("-rtsdtr");
+	else {
+		if (fmt >= BSD)
+			bput("rtsdtr");
+	}
 
 	/* special control characters */
 	cc = tp->c_cc;
diff --git a/bin/stty/stty.1 b/bin/stty/stty.1
index a0f76fe2bfd1..1863c2286176 100644
--- a/bin/stty/stty.1
+++ b/bin/stty/stty.1
@@ -145,6 +145,8 @@ Assume a line without (with) modem
 control.
 .It Cm crtscts Pq Fl crtscts
 Enable (disable) RTS/CTS flow control.
+.It Cm rtsdtr Pq Fl -rtsdtr
+Enable (disable) asserting RTS/DTR on open.
 .El
 .Ss Input Modes:
 This corresponds to the c_iflag in the termios structure.