William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ un...@physics.ubc.ca
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/
On Wed, 10 May 2017, Deven Hickingbotham wrote:
On 5/9/2017 2:41 PM, Bill Unruh wrote:
Besides I do not think a RPi has an RTC.
You are correct that a standard RPi does not have a RTC.
However, the GPS board I am using does.
OK, then, depending on how good the rtc is, and how long theRPi is switched
off, you will start up with the time being very close to UTC. Your worry
about startup seems misplaced. And certainly, if your system goes out by .1
sec after startup, something is very wrong and doing a step is not really
going to help matters.
chrony witt test the rtc and figue out its drift rate and offset. The main
problem is temp diff of the rtc between the rpi running and off. And unless
you have them iside a box, the rtc is pretty well ventilated.
Anyway, why not state what your requirements are which may help us figure out
what the best way of meeting those. Under steady state, chrony can keep your
system within a few usec of UTC. What do you need?
u have a GPSwith a PPS and, I presume NMEA output. You have only sporadic
network connectivity. Is the RPi usually on or off? What do you need when it
is on? Why is it off? How are you setting up the GPS--- both PPS and NMEA? How
are you coupling it to the RPi? What program? gpsd? Homegrown? interrupt? ...
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