[ntp:questions] More than one PPS source on Raspberry Pi?

Brian Utterback brian.utterback at oracle.com
Mon Dec 4 21:25:26 UTC 2017

Doesn't adding a second PPS signal mean that the accuracy can only go 
down? If the two PPS signals are really in sync then they will be 
clocking essentially simultaneously. They won't get serviced 
simultaneously so one will either be ignored or will be serviced after a 

On 12/4/2017 12:02 PM, Paul J R wrote:
> The answer is no and yes (and also maybe)..
> no because the current pps-gpio driver only loads a single pin (though 
> it could be extended to load more than one, but i dont think anyones 
> done that).
> yes because the other way it could be achieved is to create a second 
> module called pps-gpio2 and then init that with a different pin 
> config, and that wouldn't be overly hard and possibly easier than 
> trying to extend the existing driver (depending on knowledge of kernel 
> drivers).
> Lastly, maybe because im unaware of what hardware limits the rpi might 
> have which might get in the way of doing something like that (from 
> what i've read, every pin is capable of being configured for 
> interrupts, so it sounds like it should be possible)
> On 05/12/17 03:35, Frank Wayne wrote:
>> Has anyone tried to use more than one PPS source at the same time on 
>> a Raspberry Pi? The device tree overlay pps-gpio does not seem to 
>> support more than one instance. That is, if my config.txt specifies 
>> two instances of pps-gpio for different GPIO pins, only /dev/pps0 is 
>> created.
>> The documentation for pps_gpio is limited or missing, and the 
>> Raspberry Pi forum and the LinuxPPS list have not helped.
>> If pps-gpio cannot do it, is there another way to get PPS devices for 
>> Raspbian or another OS that will run on a Pi?
>> Frank Wayne
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