[ntp:questions] Atom PPS with parallel port

Rob nomail at example.com
Sun Feb 23 17:35:40 UTC 2014

David Lord <snews at lordynet.org> 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.

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