Xref: utzoo comp.dcom.modems:1241 comp.sys.att:2213 comp.unix.questions:5182
Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!gargoyle!oddjob!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.dcom.modems,comp.sys.att,comp.unix.questions
Subject: dial in / out on same line
Summary: how to implement it
Message-ID: <10330@mimsy.UUCP>
Date: 25 Jan 88 07:21:54 GMT
References: <142@mccc.UUCP> <564@virginia.acc.virginia.edu> <10321@mimsy.UUCP> <148@mccc.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 124

I have written about this before, but let me try for concise.  The
trick is to have two flags per line.  One says `pretend carrier is
present'; the other says `this line is being used by a dialout
program'.  In my current implementation, the former is done with
the TS_CARR_ON flag, and the latter with an XX_inout[] array (where
XX is the device; see below).

In the device driver, opening the `normal' line works like this:

	for (;;) {
		if (dialout is not in use) {
			assert ready;	/* let the modem answer the phone */
			if (there is a carrier)
				break;
		}
		wait;
	}
	open the line;

The dialout code looks like this:

	if (the line is in use)
		error(busy);
	assert ready, dialout, and software carrier;
	open the line;

The carrier-detect status change code looks like this:

	if (there is a real carrier) {
		if (dialout in use) {
			/*
			 * We must have got through, so let us know when/if
			 * the line drops.
			 *
			deassert software carrier;
			 *
			 * The software carrier is `deasserted' by doing
			 * nothing.  When the carrier status changes
			 * again it will be to `there is no real carrier'
			 * and we will do the `else' below.
			 */
		}
	} else {
		hang up the line as usual;
	}

and the close code says

	if (this is the dialout line || hangup-on-close set) {
		drop the line, pausing long enough for
			the modem to see it;
	}
	do close protocol;
	if (this is the dialout line) {
		deassert dialout;
		reset software carrier from saved original state;
		wake up anyone waiting for dialin use;
			/* this last so it can reassert ready */
	}

In practise, this is implemented as follows, using the DMF driver
as an example:

dmfopen:
	if ((tp->t_state & TS_ISOPEN) == 0) {
		... set initial state ...
	} else if ((tp->t_state & TS_XCLUDE || dial) && u.u_uid != 0)
		return (EBUSY);
	bit = 1 << (unit & 7);
	s = spltty();
	if (dial)
		dmf_inout[dmf] |= bit;
	/* this is an Ultrix compatibility hack.  FNDELAY is set if dial */
	if (flags & FNDELAY) {
		(void) dmfmctl(dev, DMF_ON, DMSET);
		tp->t_state |= TS_CARR_ON;
	} else {
		for (;;) {
			if ((dmf_inout[dmf] & bit) == 0 &&
			    (dmfmctl(dev, DMF_ON, DMSET) & (DMF_CAR<<8) ||
			     dmfsoftCAR[dmf] & bit))
				break;
			tp->t_state |= TS_WOPEN;
			sleep((caddr_t)&tp->t_state, TTIPRI);
				/* stock drivers use &tp->t_rawq; beware */
		}
		tp->t_state |= TS_CARR_ON;
	}
	splx(s);
	return ((*linesw[tp->t_line].l_open)(dev, tp));

dmfclose:
	(*linesw[tp->t_line].l_close)(tp);
	(void) dmfmctl(unit, DMF_BRK, DMBIC);
	if (tp->t_state&TS_HUPCLS || (tp->t_state&TS_ISOPEN)==0 || dial) {
		(void) dmfmctl(unit, DMF_OFF, DMSET);
		timeout(wakeup, (caddr_t)&tp->t_flags, hz);
		sleep((caddr_t)&tp->t_flags, PZERO - 1);
	}
	ttyclose(tp);
	if (dial) {
		dmf_inout[unit >> 3] &= ~(1 << (unit & 7));
		wakeup((caddr_t)&tp->t_state);
			/* again, 4.3 drivers use &tp->t_rawq */
	}
	return (0);

dmfrint, if carrier status changes:

		if (addr->dmfrms & DMF_CAR)	/* have carrier */
			(void)(*linesw[tp->t_line].l_modem)(tp, 1);
		else if ((dmfsoftCAR[dmf] & (1 << unit)) == 0 &&
		    (*linesw[tp->t_line].l_modem)(tp, 0) == 0) {
			... drop the line ...

How `dial' is determined is up to the driver.  I used separate
major device numbers, fearing to run out of minor devices if I took
a bit (particularly in the case of the 4.3BSD dmf driver, which
already uses bit 7 to identify the printer port).  Since we are
now converting to Annex terminal servers, I would probably use
a bit now.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris