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- To: chrony-users@xxxxxxxxxxxxxxxxxxxx, Bill Unruh <unruh@xxxxxxxxxxxxxx>
- Subject: Re: [chrony-users] Multi-PPS+RTC Setup Questions
- From: Matt Corallo <ntp-lists@xxxxxxxxxxxxxxx>
- Date: Tue, 29 Sep 2020 17:59:24 -0400
- Cc: hmurray@xxxxxxxxxxxxxxx
- Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mattcorallo.com; s=1601414498; t=1601416764; bh=KLTcKfWRXhvk0X23guLz3QSy0uRsa0dTQYsh9jfOTS0=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=ZupuL8zX1nG3fzohnfCx27XlgKxEx8B7xTxAej7g2TjPC5ZxtsPKnvyQbC5MX9TKQ RLWZxSh0wycToTKNb3RLXb4YVIKKXIExwpzzGipqqPnRKUWn3k8XiXkTm7cZMPbzJ+ 14vrrOjOngaeVzq/ATgKodRqIlqLWD+B+ROu9LhYITOtG/yV+nqQULq6KWKgIy9dya aOWgSm54nqJBnL5zDsxbz+0OKaoSyuZu0vhybhS8YMP5o7H5MWZ33i8524zSLSPmT1 0cG29vrwlRgaSJ/IcEBgp9oaPUGAsaX9gGwWdmRzSKAtyJdje/xp1vdqL+wgXBbkhE NB5DBhT8AAkkg==
NMEA, at least on many systems also seems to vary based on the time required to calculate the fix, which varies based on
sats and is presumably some good chunk of a second already (cause why would you overspec the CPU in the GPS receiver to
calculate much quicker than that?).
On 9/29/20 5:35 PM, Bill Unruh wrote:
There is no way that pps from any gps
chipset should be out by 30us and variable at that level.
Just a note, at least in my case, the PPS outputs are not variable at 30us, they are fixed at a 30us offset from each
other, and variable within reason for the system (embedded with poor system clock stability, but not too slow with only
some reasonable interrupt processing latency). Indeed, I agree its a bonkers result, but absent any other evidence, I'm
left blaming u-blox. Maybe its the 9-series just being too new and buggy (I've noticed a number of other bugs in its
output, though all incredibly trivial ones).
Matt
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