Re: AW: AW: [chrony-users] chrony: Use of RTC trimming together with ntpdate: A Bad Thing ?

[Ed W <lists@xxxxxxxxxxxxxx>]

On 31/08/2011 16:48, Bill Unruh wrote:
> On Wed, 31 Aug 2011, Ed W wrote:
> ...
>>
>> I'm building something completely different, but I have similar
>> requirements to try and get accurate time at boot for an unattended
>> router type device.  I'm also considering including a BlueNext GPS that
>> appears to come in around the $16 mark (if someone knows of a cheaper
>> source for USB GPS units then interested to hear?)
>
> With or without antenna? And how do you get the timing info out? (usb
> is not
> so good at interrupts)

There is no PPS on the bluenext thing, so you are constrained to NMEA
accuracy.  As such it's definitely not hyper accurate, but it will get
you within single ms accuracy if you adjust the offset manually.

For many requirements this is satisfactory....

Does anyone know if there are any mass market USB GPS devices which *do*
have a PPS pulse?  This potentially gets the accuracy down to a few ms
without needing a manual offset correction?  Having scanned the options
I don't see any which do this?  I accept that USB PPS would be poor by
the standards of other PPS options, but sometimes something is better
than nothing...

Cheers

Ed W



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