[time-nuts] Linux PPS clues?

Attila Kinali attila at kinali.ch
Thu Oct 20 14:18:05 EDT 2016

On Thu, 20 Oct 2016 10:48:28 +0000
Ilia Platone <info at iliaplatone.com> wrote:

> the only essential task is sampling and logging into an usb drive. the 
> timestamps must be as accurate as possible with the GPS reference clock. 
> This for an undefined number of devices.

What kind of events are they, what do you need to do with them and 
what do you want to store?

> Since this 100KHz is a starting point, I must know how fast can be the 
> event rate. Linux Clock tick on some boards should be 100ns for example, 
> giving a maximum event rate of 5MHz.

For 5MHz event rate, you will need specialized hardware (either
something on the uP or an FPGA) to do the heavy lifting and provide
a stream of badged data to the processor.

> I must only ensure if the kpps/gpsd system can have a good accuracy for 
> 5-8 hours. I own a dozen of the Glomation sbc3130s boards (100MHz / 
> 12MHz GPIO speed / NXP3130 uC). If these boards can do this work, I'd be 
> happy.

They probably can, but also probably not the way you imagine.
Running linux, they will only have enough power to pipe the data
through if you have 5Mevent/s. Even 100kevent/s will be a bit
difficult, depending on what needs to be done. If you don't run
linux on those, then they should have plenty of processing power
to do almost everything you want, unless you want 5Mevent/s.

			Attila Kinali
Malek's Law:
        Any simple idea will be worded in the most complicated way.

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