Is snp(4) in working order?

From: Bertrand Petit <>
Date: Thu, 19 Aug 2021 16:12:24 +0200
	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.]

%!PS -- Bertrand Petit
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Received on Thu Aug 19 2021 - 14:12:24 UTC

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