If CDSR_OFLOW (stty dsrflow) is enabled on one or both sides of a

null-modem tty device emulate the speed settings faithfully.

The speed is emulated independently for the two directions, using
the slower of the local sides ispeed and the remote sides ospeed.

The emulated speed takes settings of bits/char, parity and stopbit
into account.

Inspired by:	The BSD-DK Editor Celebrity Deathmatch Contest

1 files changed, 128 insertions, 14 deletions

diff --git a/sys/dev/nmdm/nmdm.c b/sys/dev/nmdm/nmdm.c
index ccb3467..cd3b5f3 100644
--- a/sys/dev/nmdm/nmdm.c
+++ b/sys/dev/nmdm/nmdm.c
@@ -55,13 +55,15 @@ __FBSDID("$FreeBSD$");
 
 MALLOC_DEFINE(M_NLMDM, "nullmodem", "nullmodem data structures");
 
-static void 	nmdmstart(struct tty *tp);
-static void 	nmdmstop(struct tty *tp, int rw);
-static void 	nmdminit(struct cdev *dev);
+static d_close_t	nmdmclose;
 static t_modem_t	nmdmmodem;
-
 static d_open_t		nmdmopen;
-static d_close_t	nmdmclose;
+static t_oproc_t	nmdmoproc;
+static t_param_t	nmdmparam;
+static t_stop_t		nmdmstop;
+
+static void 	nmdminit(struct cdev *dev);
+
 
 static struct cdevsw nmdm_cdevsw = {
 	.d_version =	D_VERSION,
@@ -82,6 +84,13 @@ struct softpart {
 	int			nm_dcd;
 	struct task		pt_task;
 	struct softpart		*other;
+	struct callout		co;
+	u_long			quota;
+	u_long			accumulator;
+	int			rate;
+	int			credits;
+
+#define QS 8	/* Quota shift */
 };
 
 struct	nm_softc {
@@ -141,6 +150,28 @@ nmdm_clone(void *arg, char *name, int nameen, struct cdev **dev)
 }
 
 static void
+nmdm_timeout(void *arg)
+{
+	struct softpart *sp;
+
+	sp = arg;
+
+	if (sp->rate == 0)
+		return;
+
+	/*
+	 * Do a simple Floyd-Steinberg dither here to avoid FP math.
+	 * Wipe out unused quota from last tick.
+	 */
+	sp->accumulator += sp->credits;
+	sp->quota = sp->accumulator >> QS;
+	sp->accumulator &= ((1 << QS) - 1);
+
+	taskqueue_enqueue(taskqueue_swi_giant, &sp->pt_task);
+	callout_reset(&sp->co, sp->rate, nmdm_timeout, arg);
+}
+
+static void
 nmdm_task_tty(void *arg, int pending __unused)
 {
 	struct tty *tp, *otp;
@@ -166,14 +197,18 @@ nmdm_task_tty(void *arg, int pending __unused)
 	if (tp->t_state & TS_TTSTOP)
 		return;
 	while (tp->t_outq.c_cc != 0) {
+		if (sp->rate && !sp->quota)
+			return;
 		if (otp->t_state & TS_TBLOCK)
 			return;
+		sp->quota--;
 		c = getc(&tp->t_outq);
 		if (otp->t_state & TS_ISOPEN)
 			ttyld_rint(otp, c);
 	}
 	if (tp->t_outq.c_cc == 0)
 		ttwwakeup(tp);
+
 }
 
 /*
@@ -199,20 +234,24 @@ nmdminit(struct cdev *dev1)
 	pt->part2.dev = dev2;
 
 	pt->part1.nm_tty = ttymalloc(pt->part1.nm_tty);
-	pt->part1.nm_tty->t_oproc = nmdmstart;
+	pt->part1.nm_tty->t_oproc = nmdmoproc;
 	pt->part1.nm_tty->t_stop = nmdmstop;
 	pt->part1.nm_tty->t_modem = nmdmmodem;
+	pt->part1.nm_tty->t_param = nmdmparam;
 	pt->part1.nm_tty->t_dev = dev1;
 	pt->part1.nm_tty->t_sc = &pt->part1;
 	TASK_INIT(&pt->part1.pt_task, 0, nmdm_task_tty, pt->part1.nm_tty);
+	callout_init(&pt->part1.co, 0);
 
 	pt->part2.nm_tty = ttymalloc(pt->part2.nm_tty);
-	pt->part2.nm_tty->t_oproc = nmdmstart;
+	pt->part2.nm_tty->t_oproc = nmdmoproc;
 	pt->part2.nm_tty->t_stop = nmdmstop;
 	pt->part2.nm_tty->t_modem = nmdmmodem;
+	pt->part2.nm_tty->t_param = nmdmparam;
 	pt->part2.nm_tty->t_dev = dev2;
 	pt->part2.nm_tty->t_sc = &pt->part2;
 	TASK_INIT(&pt->part2.pt_task, 0, nmdm_task_tty, pt->part2.nm_tty);
+	callout_init(&pt->part2.co, 0);
 
 	pt->part1.other = &pt->part2;
 	pt->part2.other = &pt->part1;
@@ -257,6 +296,84 @@ nmdmopen(struct cdev *dev, int flag, int devtype, struct thread *td)
 }
 
 static int
+bits_per_char(struct termios *t)
+{
+	int bits;
+
+	bits = 1;		/* start bit */
+	switch (t->c_cflag & CSIZE) {
+	case CS5:	bits += 5;	break;
+	case CS6:	bits += 6;	break;
+	case CS7:	bits += 7;	break;
+	case CS8:	bits += 8;	break;
+	}
+	bits++;			/* stop bit */
+	if (t->c_cflag & PARENB)
+		bits++;
+	if (t->c_cflag & CSTOPB)
+		bits++;
+	return (bits);
+}
+
+static int
+nmdmparam(struct tty *tp, struct termios *t)
+{
+	struct softpart *sp;
+	struct tty *tp2;
+	int bpc, rate, speed, i;
+
+	sp = tp->t_sc;
+	tp2 = sp->other->nm_tty;
+
+	if (!((t->c_cflag | tp2->t_cflag) & CDSR_OFLOW)) {
+		sp->rate = 0;
+		sp->other->rate = 0;
+		return (0);
+	}
+
+	/*
+	 * DSRFLOW one either side enables rate-simulation for both
+	 * directions.
+	 * NB: the two directions may run at different rates.
+	 */
+
+	/* Find the larger of the number of bits transmitted */
+	bpc = imax(bits_per_char(t), bits_per_char(&tp2->t_termios));
+
+	for (i = 0; i < 2; i++) {
+		/* Use the slower of our receive and their transmit rate */
+		speed = imin(tp2->t_ospeed, t->c_ispeed);
+		if (speed == 0) {
+			sp->rate = 0;
+			sp->other->rate = 0;
+			return (0);
+		}
+
+		speed <<= QS;			/* [bit/sec, scaled] */
+		speed /= bpc;			/* [char/sec, scaled] */
+		rate = (hz << QS) / speed;	/* [hz per callout] */
+		if (rate == 0)
+			rate = 1;
+
+		speed *= rate;
+		speed /= hz;			/* [(char/sec)/tick, scaled */
+
+		sp->credits = speed;
+		sp->rate = rate;
+		callout_reset(&sp->co, rate, nmdm_timeout, sp);
+
+		/*
+		 * swap pointers for second pass so the other end gets
+		 * updated as well.
+		 */
+		sp = sp->other;
+		t = &tp2->t_termios;
+		tp2 = tp;
+	}
+	return (0);
+}
+
+static int
 nmdmmodem(struct tty *tp, int sigon, int sigoff)
 {
 	struct softpart *sp;
@@ -264,14 +381,11 @@ nmdmmodem(struct tty *tp, int sigon, int sigoff)
 
 	sp = tp->t_sc;
 	if (sigon || sigoff) {
-		if (sigon & SER_DTR) {
+		if (sigon & SER_DTR)
 			sp->other->nm_dcd = 1;
-			ttyld_modem(sp->other->nm_tty, sp->other->nm_dcd);
-		}
-		if (sigoff & SER_DTR) {
+		if (sigoff & SER_DTR)
 			sp->other->nm_dcd = 0;
-			ttyld_modem(sp->other->nm_tty, sp->other->nm_dcd);
-		}
+		ttyld_modem(sp->other->nm_tty, sp->other->nm_dcd);
 		return (0);
 	} else {
 		i = 0;
@@ -291,7 +405,7 @@ nmdmclose(struct cdev *dev, int flag, int mode, struct thread *td)
 }
 
 static void
-nmdmstart(struct tty *tp)
+nmdmoproc(struct tty *tp)
 {
 	struct softpart *pt;