George R. Kasica <[email protected]> writes: >On Wed, 31 Dec 2008 00:20:45 GMT, "David J Taylor" ><[email protected]> wrote:
>>Unruh wrote: >>> "David J Taylor" >>[] >>>> With just the reference clock type 20, I get the accuracy needed. >>>> The PPS line from the GBS-18 LVC is wired to the DCD line of the >>>> serial port. In my ignorance, I don't see why you even need the SHM >>>> driver, but as I said before, I'm no expert! I don't see why my >>>> system picks up the PPS from just the type 20 driver, and yours does >>>> not. >>> >>> >>> Because you have the PPS kernel patch installed or it was >>> automatically >>> instaled in BSD? The OP does not and does not want to. >> >>Thanks. Yes, I had to recompile the FreeBSD kernel to include this patch. >>I must have thought at the time that it was mandatory, or was advised to >>do this. >I'd be happy to put it in here, but doing so with the Fedora Core 9 >RPM based code is not something I'm familiar with. I'm used to working >with straight source code for kernels ie make make install type steps >(don't take those literally please I know the steps) or just leaving >the RPMs alone. I just am not sure how or if the PPS patches I've seen >will apply to the kernel version here on the FC9 box or how it will >affect the system-obviously breaking it is not an option - well, it >always is but not a good one since it archives a ton of weather data >:). I think it will gain you nothing over the shm option, except you will be sitting there worrying and watching your computer compiling a kernel. However, has anyone done tests on the serial port interrupt to see how much latency there is in that? Ie, If I use, say, shmpps and I trigger the serial control line at time t, what is the time t+dt that shmpps reports as the time of the trigger? And what is the fluctuation in dt? On the parallel port interrupt service routine I have done that and the result was about 0-2usec. (in fact I suspect most of the noise in at least the short term fluctuation of ntpd is from that source). But shmpps and gpsd have a whole layer of serial port driver interposed between the interrupt and the report. Does that made a difference? >If someone can detail what needs to happen I'd be happy to run it that >way, though as of right now I'm not sure what it would gain me over >the shm driver option. FYI the kernel I'm running is: >2.6.27.7-53.fc9.i686 #1 SMP >and loaded rpms are: >kernel-devel-2.6.27.7-53.fc9.i686 >kernel-headers-2.6.27.7-53.fc9.i386 >kernel-firmware-2.6.27.7-53.fc9.noarch >kernel-2.6.27.7-53.fc9.i686 >kernel-doc-2.6.27.7-53.fc9.noarch >-- >===[George R. Kasica]=== +1 262 677 0766 >President +1 206 374 6482 FAX >Netwrx Consulting Inc. Jackson, WI USA >http://www.netwrx1.com >[email protected] >ICQ #12862186 _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
