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

[Jim Harman]

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