[time-nuts] GPS module recommendation for Pi timing

[Bob kb8tq]

Hi

Pretty much any generic GPS module will get you to 1 ms without a lot
of effort. There is certainly no need for the M9F or M9T sort of parts. 
A typical module will deliver a pps signal that is better than 100 ns as
far as timing. 

How good you can do via serial on a Pi depends a bit on how loaded it 
is. “Microsecond" level performance is possible. 

I’d target low cost over performance in this case …..

Are you laying out a board for your gizmo? If so, there are a number of
drop in solutions for not a whole lot of money. 

Bob

> On Mar 13, 2020, at 10:06 AM, Brian Lloyd <brian at lloyd.aero> wrote:
> 
> I have an application where I need to synchronize the internal TOD RTC in a
> raspberry pi and need to pick a GPS module. We are building our own
> hardware but still using the Pi so interconnection will be via GPIO/serial.
> We won't try to use USB.
> 
> This is not an NTP application. These units will be in the field and will
> most likely not have Internet access. I need their clocks to be pretty
> close. I am shooting for 1ms ... if possible.
> 
> The new M9F and M9T modules from Ublox are a bit pricey. The M8T is a bit
> more reasonable. OTOH I realize there are limits to how tightly I can
> control the Pi's RTC and will run into diminishing returns, so even the M8T
> might be overkill.
> 
> Has anyone here figured out what the reasonable limit is for timing on a
> Pi, and what makes sense for a timing module for an application like this?
> 
> Thanks.
> 
> -- 
> 
> 
> 
> Brian Lloyd
> 706 Flightline
> Spring Branch, TX 78070
> brian at lloyd.aero
> +1.210.802-8FLY (1.210.802-8359)
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