Additional pps-gpio

[Hal Murray]

devel at ntpsec.org said:
> As far as I understand the sources, setting up an echo allows a PPS client
> to register a callback function with the PPS device to be called when a PPS
> event happens.  The default echo function simply outputs "echo: assert" or
> "echo: clear".  I guess one could indeed toggle a GPIO from a suitably
> defined PPS client. 

Thanks.

It may be easier to experiment with a real serial port since it would be easy 
to pick one of the output modem control signals.

With gpio we could make the dtoverlay line take 2 pin numbers.  It shouldn't 
be a big deal, but it's another complication.  As a hack, we could just use 
the next pin number.  I think the hardware is safe if you pick a wrong pin 
number.  If the dtb isn't setup right, the gpio bit isn't connected to the 
output pin.

The other hack we would need to to is patch the code in ntpd that sets up the 
PPS stuff not to turn off the edge it doesn't need so the output pin can get 
reset to be ready for the next time.




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