At Wed, 24 Aug 2011 13:34:32 -0700, AGC <agcarver+netbsd%acarver.net@localhost>
wrote:
Subject: Re: DCD as an alternate /dev device?
>
> From some of the discussions on the ntpd list it appears that there
> should be an ability to open the port twice. However, the discussions
> it also appears that the port is actually split in two pieces by the
> underlying OS. The TX/RX is available via one device and the signals
> (especially DCD) is available by a separate device. One user
> commented that FreeBSD happens to perform this breakout.
I don't know if this will help for your specific problem, but in general
NetBSD does have two /dev interfaces for each physical port, one which
blocks waiting for DCD and the other which does not. See tty(4) on
NetBSD and pay attention to the description of /dev/dtyXX and note the
differences between that interface and the one for /dev/ttyXX.
Note though that assertion of DCD will be ignored on /dev/ttyXX
(i.e. leaving the blocked process blocked) if the corresponding
/dev/dtyXX is open -- and subsequent loss of DCD will be reported to
/dev/dtyXX while the latter is open (and the process blocked on
/dev/ttyXX will wait until the next DCD event which occurs without the
corresponding /dev/dtyXX being open).
This is of course exactly what you want for bi-directional use of a
proper modem that's used for normal dial-up logins, uucp, cu/kermit,
etc.
I'm not sure how the kernel PPS_SYNC and NTP options affect this.
I would think you want to use /dev/dtya at the very least as the PPS
device, but I didn't read through enough of sys/ic/com.c to see how that
would affect the PPS_SYNC stuff, if at all.
There's very little good documentation about this kernel NTP and
PPS_SYNC stuff with nothing in tty(4) and very little in options(4), and
nothing about the pps mentioned in conf/majors (no pps(4), though is it
the pps "driver" for ppbus(4)?).
--
Greg A. Woods
Planix, Inc.
<woods%planix.com@localhost> +1 250 762-7675 http://www.planix.com/
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