On Wed, 31 Jul 2019 13:48:28 +0100, NY wrote:

> "druck"  wrote in message
> news:qhrg3s$tef$1@dont-email.me...
>> On 29/07/2019 18:10, A. Dumas wrote:
>>>  wrote:
>>>> can anyone tell me if the new RaspberryPi4 is capable of hardware
>>>> timestamping according to IEEE1588/PTP?
>>>
>>> I'm sure it can be a slave, it's just a Linux computer, but the Pi
>>> (any version) doesn't even have a hardware clock, so probably useless
>>> as a ptp master.
>>
>> There is a battery backed RTC module for the Pi, and a number of people
>> have interfaced to GPS based time signals. So there is no reason why a
>> Pi can't be used for this.
>
> I wonder how much extra it would add to the purchase price of a Pi to
> include an RTC powered by a capacitor to keep things going until the Pi
> has rebooted. If you have a permanent internet connection, it's no
> problem because as soon as the Pi boots it resyncs with a time source on
> the internet, but it can be a problem if a Pi is used with an
> intermittent internet connection.
>
> OK, so we had a very unusual case: no ADSL/VDSL internet connection in
> our new house for a few weeks, so I was relying on tethering my PC and
> Pi to the mobile phone internet. That was fine until my Pi rebooted when
> there was no mobile in range, and its time reset itself to an hour or so
> earlier. That screwed up the data for my weather station logging that my
> Pi does: I had to go in and hand-modify the time stamps on some readings
> until I realised the problem and synced the Pi to NTP.
>
> Given the very portable nature of a Pi, and therefore the chance that it
> may be used on projects that don't have an internet connection, it needs
> to be resilient to reboots when it's not able to see an NTP source or
> when the date/time can't be modified manually.
>
> But maybe an external RTC for those special cases is more cost-effective
> than adding it to the Pi where it is not needed for situations where
> there is access to NTP.

Hanging a GPS receiver on it could be a neat solution.

Are there any suitably packaged units and interfacing software available?


--
Martin    | martin at
Gregorie  | gregorie dot org

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