LKM Timemark Driver

[Udo van den Heuvel]

On 28-08-18 10:06, Hal Murray via devel wrote:
> Could somebody please review this discussion.  I'm trying to catch up.  I can
> follow most of the details, but I'm missing the big picture.
> 
> What GPS device is involved? 

U-blox.

> Is there a handy board?

e.g. https://www.csgshop.com/product.php?id_product=240

>  What does it actually
> do?


Receive concurrent multi GNSS.
Provide PPS to PC.
Provide timestamping from pulses sent back to the receiver.
Perhaps more.

>  I'm guessing it time stamps an input pin.  (Some other GPS unit does
> that.  I forget which one.)

Would be interesting to explain why we need ability to send pulses from 
ntpd via kernel.

> Does the PPS logic on the Raspberry Pi use a counter to avoid interrupt
> latency?

Dunno.

> What does the proposed kernel mod do?  I'd guess grab a time stamp
> before/after flapping an output pin.

The 'PC' needs to know when the pulse is sent.
Then the time of pulse reception info is returned from the GPS receiver.
Combining both can help set time.


Udo