On 2014-02-23, Rob <[email protected]> wrote: > David Lord <[email protected]> wrote: >> Rob wrote: >>> David Lord <[email protected]> wrote: >>>> Rob wrote: >>>>> I would like to use the Atom driver (22) on a Linux system with a >>>>> parallel port. It is not clear to me from the scattered info I have >>>>> found on internet if this is going to work. >>>>> >>>>> Using a modern Linux kernel with the PPS module, is it possible to >>>>> symlink /dev/pps0 to a parallel port device and then connect the PPS >>>>> signal to the ACK input (pin 10)? >>>>> >>>>> If not, what else is required to get this working? >>>>> >>>>> Examples always refer to the use of a serial port DCD input, but for >>>>> best accuracy (in the microsecond range) I think the parallel port >>>>> is better. >>>>> (no RS232 drivers/receivers, no funny UART that may delay interrupts) >>>>> >>>>> Any other suggestions for an accurate PPS input? >>>> On NetBSD with stock ntpd, pre 2010, I did comparisons of >>>> pps from Sure GPS with output from dcd at ttl level vs the >>>> "serial" dcd but didn't really see any consistent difference. >>> >>> Did you try the parallel port? >>> I am interested not only in jitter but also in any constant offset >>> between the PPS pulses and system time on different systems (possibly >>> using different makes of serial card). 4-6 us would be good enough for >>> my purpose, but it would not be good when one system had a 10us offset >>> because of a propagation delay in a linedriver/receiver. >> >> Yes, and from archived ntp.conf at that time /dev/pps* at ppbus >> but I also tried without ppbus and had a symlink to /dev/lpt* >> >> For past couple of years I have pps2 -> /dev/tty00 and there >> is no ppbus in my recent kernels so I guess it was from a >> custom kernel. > > I am not familiar with BSD speak and we are not considering use of BSD. > > It appears that with the current Linux PPS and the modules that are > included after 2.6.38 it should not be symlinked but the module directly > creates the /dev/pps* devices via udev. That is fine with me as well. > I only wonder why a simple cookbook is not readily available on the > linuxpps site or even as a comment in the sourcefile.
/usr/src/linux*/Documentation/pps/pps.txt ? cookbook for what? ntp use? > > Now that I have it, the next step is to test things. > In fact I can do that using the Datum 9360 as it also has a PPS input > and a measurement mode where it displays the offset between the pulses > on that input and its internal PPS. _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
