[time-nuts] Re: pps pulse timestamp device

[Peter Bell]

Just out of interest, did you characterize the PLL jitter on this part?
When I was experimenting
with STM32s I found there was quite significant clock jitter even with the
spread-spectrum clocking
turned off. It did average to zero over any reasonable sampling period, but
it also made individual
timestamps quite noisy.

- Pete


On Mon, Feb 19, 2024 at 3:10 AM Jeremy Elson via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi Juan,
>
> The STM32G4 is a great device for timestamping - it's what my timestamper
> uses! It can run up to 170MHz which gives you a timing resolution of just
> under 6ns.
>
> As you noticed, some of the models (e.g. the STM32G474) do have the HRTIM
> peripheral, and that was the source of my original excitement for
> time-nuttery. It has a DLL of 32x on top of the 170MHz system clock, which
> made me *think* I could use it to get 184ps resolution from a $10 chip.
> Unfortunately when I sat down to finally write the code I realized that the
> HRTIM only gives you that kind of resolution for *output* waveforms. Input
> capture still runs at the system clock frequency.
>
> In any case, I think it's still impressive to get 6ns resolution out of a
> $5 chip (the STM32G431). My code and schematics are all open source; see:
> https://github.com/jelson/rulos/blob/main/src/app/timestamper/timestamper.c
> . My prototype board uses the STM32G431, with a 10MHz reference clock input
> from the oscillator of your choice. I've used both GPSDOs and Rubidium
> LPRO-101's. My board has a small analog circuit that changes the 0-centered
> AC input of the reference clock to an above-zero waveform that can be used
> as the stm32's system clock. The stm32 chip has an onboard PLL that I
> configure to multiply the 10MHz ref clock up to a 170MHz system clock. Then
> I use the input capture feature of the chip to acquire timestamps.
>
> -Jeremy
>
>
>
> On Thu, Feb 15, 2024 at 8:04 AM Juan Solano via time-nuts <
> time-nuts at lists.febo.com> wrote:
>
> > Thanks a lot guys for pointing me at the TICC, definitely I will have a
> > look.
> >
> > Jeremy, interesting that you are using an STM32. I have an STM32G4
> > lying around and I should have looked into it as I think it has some
> > high resolution timer that perhaps could be handy for this kind of
> > stuff, is that what you are using in your project? Your oscillator
> > recomendation sounds great!
> >
> > Regards,
> > Juan.
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