On Wed, 09 Dec 2020 10:35:11 +0000, Adam Funk wrote:

> On 2020-12-07, Martin Gregorie wrote:
>
>> On Mon, 07 Dec 2020 15:55:32 +0000, Ahem A Rivet's Shot wrote:
>>
>>> On Mon, 07 Dec 2020 14:50:01 +0000 Adam Funk 
>>> wrote:
>>>
>>>> I was just wondering about what kind of situation needs the external
>>>> clock so the time is accurate *before* NTP starts working.
>>>
>>>  It rather depends on how long might elapse before reaching a time
>>> server, if there's any danger of that being a long time then a RTC is
>>> very helpful, if you're sure of a time server immediately after boot
>>> then it's pretty much useless.
>>
>> Don't forget that an old GPS unit, provided it has serial NMEA0183
>> output which many of them had, can be used by ntpd as a primary time
>> reference. These can be connected to an RPI via a USB-serial adapter.
>> There is a reference driver for ntpd that allows it to accept an
>> NMEA0183 primary time stream.
>
> (Not that I need something like this, but it's interesting.)
>
> I don't think an old GPS unit would be able to get a signal in my
> "network cupboard", which is a shelf in the back of a wardrobe under the
> stairs from the 1st to 2nd floors, & not on an outside wall.

The older ones often don't work in a house, and sometimes not in a forest
either, let alone under a tin roof. Modern receivers are much more
sensitive. I've just fired two GPS receivers up to prove this point:

- My old (1990) Garmin GPS2+ had no signal at all in the sill of a South-
facing window and had problems outside it as well, due mainly to the sky
view being restricted by both the house behind me and (bare) trees on the
other three sides. It did eventually find two satellites, but never
determined where it was.

- My more recent (2014) Medion S3747 PNA got enough signal on the window
sill to set its clock, but couldn't see enough satellites to determine
its position. However, when it was taken outside to the same point as the
GPS2+ it was able to determine its location and altitude after around 2
minutes.


--
--
Martin    | martin at
Gregorie  | gregorie dot org

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