[ntp:hackers] u-blox reference clock driver

Udo van den Heuvel udovdh at xs4all.nl
Mon Aug 20 13:13:09 UTC 2018

On 20-08-18 04:33, Udo van den Heuvel via devel wrote:
> On 19-08-18 18:22, Achim Gratz via devel wrote:
>> The trouble with GPIO is that it's either only
>> available on a few boards that aren't very widespread and PCI(-e) cards
>> (aside from the LTP cards)
> So LPT cards would be acceptable, usable?

In such case:

I'd see a setup with a USB connection for the data part of the setup.
PPS goes to LPT (ack pin).
LPT strobe could be used to send pulse to the ublox(*1).

At the ntpd level I could use the pps driver for pps reception, this 
should work with LPT port as well.
With some NMEA messages configured (*2) we could use these for the NMEA 
driver for just the date/time part.

Once the ublox driver is in ntpsec things change a bit:

ublox driver (see 
https://lists.ntpsec.org/pipermail/devel/2018-August/006444.html) needs 
to be changed to use LPT for PPS input and pulse output. But when will 
we see the ublox driver as it is in ntpsec?
Do I need to enter a feature request?

How to get the timemark kernel patch into Linux?
Do we really need it? (can we work around it?)


*1: see https://lore.kernel.org/patchwork/patch/237682/ where the LPT 
pps generator is declared BROKEN; this driver (see 
https://lwn.net/Articles/373193/) could still be the basis to simply 
send a pulse when called as clear edge is not so important, we can 
loosen the no-interrupt time considerably?

*2: NMEA implementation in ublox is not as complete as the ublox 
protocol is, so how to best configure the ublox? What tooling?

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