On Wed, 31 Dec 2008 17:57:25 GMT, Unruh <[email protected]> wrote:
>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? I likely have nowhere near the level of hardware/software knowledge or likely test gear to accomplish this. -- George, Ginger/The Beast Kasica(8/1/88-3/19/01, 1/17/02- ), Rosie(9/1/07- ), Merlin/MR. Tibbs(8/1/90-5/24/06, 2/10/08- ), Nazarene(6/1/99-1/28/08) Jackson, WI USA [email protected] http://www.netwrx1.com/georgek ICQ #12862186 ("`-''-/").___..--''"`-._ `6_ 6 ) `-. ( ).`-.__.`) (_Y_.)' ._ ) `._ `. ``-..-' _..`--'_..-_/ /--'_.' ,' (il),-'' (li),' ((!.-' _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
