-----Original Message-----
From: Bill Dailey
Very nice write up. I went down a similar road with my fury and Ubuntu...
And then with FreeBSD on a soekris box. Have you tried refclock drivers
instead of gpsd? I use gpsd on Ubuntu but decided to use refclock route
instead for FreeBSD. I have an overall feeling that at us and ns levels
gpsd doesn't perform as well... No evidence but is does seem like it should
be inherently slower... Probably much more important on the free bsd soekris
implementation.
Doc
=============================================
Thanks for your comments, Doc. I try to make the write sufficiently simple
but comprehensive so that I can understand it next time I need to visit
Linux!
I only use gpsd on the Linux system, and then only because it was the first
thing I discovered when searching with Google. As the precise timing is
from the PPS signal fed to the GPIO pin, with a GPIO interrupt handler, I am
forced to use that. I don't think the interrupt handler talks to the gpsd
at all, but I might be wrong. There is no DCD line on the Raspberry Pi for
gpsd to receive the PPS signal.
The FreeBSD system uses the type 20 driver (generic NMEA) for both coarse
and fine time (via kernel PPS).
As a lot of this is new to me, my understanding is not as complete as I
would like. VMS device drivers I used to understand. I think I have a
moderate knowledge of Windows and how .SYS drivers fit in, and how DLLs
might support them. What Linux "modules" are I don't yet know, so why I
need both a revised kernel /and/ modules on Linux to support PPS is
currently unknown - although my guess is that the modules are the equivalent
of Windows device drivers. Don't have the time to read up about this, but a
pointer to any easy-to-understand documentation about Linux, kernels and
modules would be welcome! My FreeBSD understanding is even less.
Cheers,
David
--
SatSignal Software - Quality software written to your requirements
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