Date: Thu, 19 Aug 2021 20:33:44 +0200 From: Gary Jennejohn <gljennjohn@gmail.com> To: Bertrand Petit <freebsd-hackers@phoe.frmug.org> Cc: freebsd-hackers@freebsd.org Subject: Re: Is snp(4) in working order? Message-ID: <20210819183344.358e1f55@ernst.home> In-Reply-To: <YR6RiRVXSTkFtIr%2B@kib.kiev.ua> References: <20210819141224.GA93701@memo2.memo.frmug.org> <YR6RiRVXSTkFtIr%2B@kib.kiev.ua>
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On Thu, 19 Aug 2021 20:14:49 +0300
Konstantin Belousov <kostikbel@gmail.com> wrote:
> On Thu, Aug 19, 2021 at 04:12:24PM +0200, Bertrand Petit wrote:
> >
> > I'm wondering if, on a 12.2 host, the snp(4) device is out of order or
> > if I'm improperly using it.
> >
> > Here is the situation: a GPS receiver connected to the host through
> > USB (umodem driver) feeding ntpd and keeping it happy. On this setup I perform
> > the following calls as root in a dedicated process:
> >
> > int a=open("/dev/cuaU0", O_RDONLY|O_NONBLOCK);
> > isatty(a); /* Yes it is */
> > int b=open("/dev/snp", O_RDONLY);
> > ioctl(b, SNPSTTY, &a);
> > int pending; ioctl(b, FIONREAD, &pending); /* Empty */
> > char buf; read(b, 1, &buf);
> >
> > I ommited error handling for brevity, all calls are successfull except read()
> > which never return.
> >
> > I expected to be able to read the same bytes stream as ntpd does but I
> > get nothing. Am I misusing the snp(4) interface or is it non-functioning?
> >
> > [As a side note: I could also had used gpsd but hooking ntpd directly
> > to the serial device yields a far better jitter.]
> Did you tried watch(8) first?
>
> I just used watch successfully over /dev/pts/N pseudoterminal.
>
I thought about using watch(8) too.
If nothing else, reading the source of /usr/src/usr.sbin/watch/watch.c
will give you a good idea about how to correctly use snp(4) in your
C-code. Pay particuar attention to how FIONREAD is used in main().
--
Gary Jennejohn
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