[time-nuts] Re: PRS-10 sawtooth correction with microcontroller

[Azelio Boriani]

The PRS10 manual offers no clue about when the offset (TO command) is
added to the measured time-tag (TT? command) so the only way to know
is to try (with the input filter off, LM0 command) and see if feeding
the sawtooth correction once a second has any effect on the PPS output
and frequency output. In my opinion the PRS10 input filter makes the
sawtooth correction unnecessary. other than taking care of occasional
hanging bridges.

On Thu, Dec 22, 2022 at 1:15 PM James Wilson via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> Thanks Jim - I wouldn’t mind having a look at the code you wrote to see if I understand the ublox commands correctly.
>
> I’ve done the survey-in step with the LEA-M8T module I have - I’ll probably have this program do it as part of startup if the GNSS module is on a cold boot and doesn’t have saved survey data.
>
> > On Dec 21, 2022, at 16:42, Jim Harman via time-nuts <time-nuts at lists.febo.com> wrote:
> >
> > I have not interfaced to the PRS-10, but I have Arduino code to extract the
> > qErr data from the UBX-TIM-TP messages. It also extracts the clock time
> > from that message in case that is of interest . It is implemented as a C++
> > Class and is easily extensible if you need to read more uBlox messages.
> >
> > One thing you also may want to consider in working with the uBlox T series
> > modules is the need to do a Survey-in to determine the exact location and
> > put the module in Fixed mode, to reduce the errors in the timepulse.
> >
> > I would be happy to share my code and setup instructions for the uBlox
> > modules if that would be helpful.
> >
> > On Wed, Dec 21, 2022 at 6:49 PM James Wilson via time-nuts <
> > time-nuts at lists.febo.com> wrote:
> >
> >> After running in many of the familiar problems of connecting a GPS timing
> >> module 1PPS signal to a PRS-10, I want try building a software sawtooth
> >> correction board. I’ve seen previous discussion of some of the commands to
> >> use for adjusting the PLL and PPS control on the PRS-10 and getting the
> >> sawtooth error from ublox GNSS modules, but not a start-to-finish
> >> description of how to put everything together.
> >>
> >> My idea to use a microcontroller with multiple UART ports; one connected
> >> to the ublox module and the other connected to the PRS-10, with level
> >> shifters as needed. The microcontroller sits between the two devices, and
> >> gets the PPS sawtooth correction info from the ublox (specifically via the
> >> UBX-TIM-TP message and its qErr field), and then adjusts the PRS-10’s PPS
> >> time offset by this value to null out the sawtooth for the next pulse.
> >>
> >> 1. At startup, configure the timing module to periodically send UBX-TIM-TP
> >> messages every second. From the PRS-10, get the current time offset value
> >> with the TO? command.
> >>
> >> 2. Listen for UBX-TIM-TP messages, and extract the qErr field. If the
> >> qErrInvalid bit is clear, compute qErr/1000 (convert from ps to ns) and add
> >> this to the stored time offset value. Push the adjusted time offset to the
> >> PRS-10 via the TO command.
> >>
> >> Has anyone built sawtooth correction for the PRS-10 and can comment on
> >> this?
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> >
> >
> >
> > --
> >
> > --Jim Harman
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