[ntp:questions] ntp & system without a rtc

unruh unruh at invalid.ca
Sat May 11 17:00:36 UTC 2013

On 2013-05-11, E-Mail Sent to this address will be added to the BlackLists <Null at BlackList.Anitech-Systems.invalid> wrote:
> John Hasler wrote:
>> E-Mail writes:
>>> The uC likely has a RTC, its just not battery backed up?
>> The Raspberry Pi has no rtc.
> Raspberry Pi has a Broadcom BCM2835 SoC (700 MHz ARM11 ARM1176JZF-S)
>   Broadcom seems to want to hold their full datasheet from public view.
>  Perhaps it doesn't have an internal RTC peripheral.

The Raspberry Pi is an ultra low cost computer. the parts are kept to a
bare minimum. Even the ethernet is a usb->ethernet link. Sticking an rtc
on the thing would up the cost, a battery of supercapacitor would up the
cost, and to little purpose since many of the uses of the Rpi do not
need even inaccurate times.
As you point out others have made an rtc for it. 
It is astonishing that one could have a full computer for $35. 
> Many ARM SoCs have an internal RTC peripheral.
>  If the product manufacturer doesn't supply an easy
>   way to connect a battery on their PCB,
>   the RTC is still in the chip.
>> There is no point in having one without a battery.
> Or a "SuperCap", depending how long it is typically off.
> Just like e.g. the PPS input on a Pi,
>  if the chip package has a RTC, and the pin/trace is
>   accessible, you could hook up a Batt/CAP.
>  ... or e.g. hook up a RTC chip on the I2C, ...
> I noticed someone make a RTC with batt for the Pi
>  Likely several others do too, {Seems so}.
> <http://www.instructables.com/id/How-to-add-a-Real-time-clock-to-the-Raspberry-Pi-o/>
> <https://www.modmypi.com/rasclock-raspberry-pi-real-time-clock-module>
> <http://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/overview>

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