[LinuxPPS] do we need hardpps?

[Udo van den Heuvel]

Hallo ALexander,

On 2010-02-06 10:31, Alexander Gordeev wrote:
>>> It seems Alexander Gordeev has already put together a patch for
>>> that?
>>> http://linux.derkeiler.com/Mailing-Lists/Kernel/2010-02/msg01444.html
>>> So the question would rather be whether it should be merged into
>>> LinuxPPS... He also posted something on this list in October, but I
>>> don't remember seeing _any_ feedback. Has anyone tried his patches?
> 
> Please consider those patches posted in October obsoleted by the new
> ones.

OK. So the latest 5 or so patches have the latest versions for all your
new pps-related features?

>> Anyone that has a testsystem to do so?
>> Maybe ask Alexander to explain here a bit more?
> 
> Sure, I'll answer any questions regarding these patches.
> It's very strange that they didn't got to this list (and I don't see
> them in the archives) because I'm subscribed and CC'd this list...

Maybe Rodolfo can explain how the archive works w.r.t. patches?

> I want to add also that this is not just the original implementation
> from David Mills. It was very far from ideal so I have to optimize it
> for speed and microsecond precision. After it is enabled, it reaches 1us
> precision in a couple of seconds and then is able to keep it within
> 1-2us for as long as needed. I've tested it under load for days on
> ordinary hardware and it never exceeded 2us.

Sounds interesting!

> Also my setup doesn't suffer from interrupt handling delays. I use very
> short PPS impulses - 10-30us - so I can just poll with disabled
> interrupts LPT IO port until the signal is cleared. A single read from
> IO port takes 1-1.5us on x86 so synchronization precision should be of
> the same order. And, of course, the wire should be short.

How does interrupt driven methods differ from this implementation w.r.t.
CPU consumption, accuracy, etc?

Since my GPS reception is still spotty, would your patches help the
kernel keep the kernel PLL going undisturbed for longer?
Or would I need to add a TCXO? (or just improve GPS reception)

Udo