[time-nuts] Generate 1 PPS signal on serial port

Anders Wallin anders.e.e.wallin at gmail.com
Tue Aug 6 10:16:46 EDT 2013

On Tue, Aug 6, 2013 at 4:07 PM, Mark C. Stephens <marks at non-stop.com.au>wrote:

> However if you are hell bent on generating PPS in software somehow (please
> let me know you plan? - curious)

Over in the hobby-CNC world where it is common to use the parallel port for
driving machine tools (mills, lathes, 3d printers) pulses with good timing
are output by LinuxCNC which sits on top of a real-time kernel (RTAI,
Xenomai, or RT-Preempt). With a well-behaving bios/cpu/motherboard
combination it is possible to achieve around 10-20 us maximum jitter - in
good cases down to 5 us. The same program run on a non-realtime kernel will
easily show 3-5 milliseconds or more of jitter.
This is relative to a clock that the real-time kernel uses for internal
timing - I am not sure if that clock can be NTP-disciplined.


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