[time-nuts] STM32 based thing (was GPSDO Alternatives)

Fabio Eboli fabioeb at quipo.it
Thu Dec 6 09:26:26 UTC 2012

Hello Michael!

Michael Tharp <gxti at partiallystapled.com> ha scritto:

> On 12/05/2012 08:03 AM, Fabio Eboli wrote:
>> I'm seriously thinking to attempt a gpsdo.
>> The platform I will try to use is the STM32F103
>> microcontroller
> Coincidentally, my previous time-nut project was built around the  
> same chip. I built a simple GPSDO using a STM32F103C with a bit of
> Here are the design documents, if you're curious:
> http://hg.partiallystapled.com/circuits/serafine/raw-file/d75ab09ca163/out/production.PDF

Thank you very much, I will study it with interest,
it will be very helpul to see what you have done.
Can I ask you more details? I didnt's understand
how you are using the timers: are you timestamping
each pps transistion using the internal clock?
Are you using the pll to obtain 72MHz (x9) for the clock?

> same as many, if not all, other GPSDOs out there. I'm reasonably  
> happy with the hardware as a GPSDO experimentation platform (but not  
> looking to sell anything at this time).

Good, to be clear my project will not be commercial
in any way, only an amateur attempt, documented as far
as my time permits. And my skills are not enough for
anything that can be sold in this field :)

> The current project, as I've mentioned before, is a self-contained  
> GPS-to-NTP server based on STM32F107, which has built-in ethernet  
> but is otherwise very similar to the F103. The finished board won't be

This is another advantage of the STM32 (or other manufacturers
cortex arm micros), one can easily port the project up to higher
specs devices; for example ST sells the stm32F4 discovery for
around 20eu that is powered by an stm32F407 that is cortex M4F
device full of ram and flash and communication ports, and that
support FPU etc, it's a 168MHz device, but I'havent checked
it's timers capability.

I will stick with the 103 for now, my goals are the basic ones:
building a counter and figuring out how to discipline a Rb,
the communication/logging/pc support software is really a big
work to do and i'm not planning to go there for some time :)


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