[LinuxPPS] Some Info about the Project I'm working on

[clemens at dwf.com]

> On Thu, Sep 06, 2007 at 06:15:09PM -0500, Adam Becker wrote:
> 
> > I wondering if and how LinuxPPS could be useful for the project I'm
> > currently working on. I'm working on an embedded PC104 stack with 3
> > Pentium M processors. What I need to do is accurately sync the clocks on
> > each of the processors because in testing the system we found that the
> > clocks drifted significantly. I have a GPS with a PPS signal. The GPS
> > data is tied to one of chips via RS232 and that chip's other 2 COMs are
> > connected to COMs on the other processors. The PPS signal is currently
> > wired to I/O pins on the parallel ports of each of the chips (this could
> > be changed) and all three currently have Ubuntu 7.04 as their OS. 
> 
> I think you don't need at all the PPS signal routed to all CPUs, but
> simply you should connect one CPU with the GPS antenna throught one
> serial line (both data and PPS signal) and then configure NTPD on that
> system in such a way it can set its clock by using the PPS signal.
> 
> Then, on the other two systems, you should configure the NTPD daemon
> in order to sync with the first CPU throught the ethernet.
> 
You dont say how close you need the timing to be on the three machines.
The ethernet would probably work, but the PPS signal to all three
would probably hold things a bit closer.

To REALLY keep things close you should consider modifying the 
motherboard so that there is only one crystal driving the clock on all
three machines.
-- 
                                        Reg.Clemens
                                        reg at dwf.com