Date: Thu, 19 Aug 2021 20:14:49 +0300 From: Konstantin Belousov <kostikbel@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: <YR6RiRVXSTkFtIr%2B@kib.kiev.ua> In-Reply-To: <20210819141224.GA93701@memo2.memo.frmug.org> References: <20210819141224.GA93701@memo2.memo.frmug.org>
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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.
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