[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [questions] Re: GPS+PPS vs NTP server, why a huge offset ?
- To: questions@xxxxxxxxxxxxx
- Subject: Re: [questions] Re: GPS+PPS vs NTP server, why a huge offset ?
- From: "Daniel O'Connor" <darius@xxxxxxxxxxx>
- Date: Fri, 17 Jun 2022 14:29:39 +0930
- Delivered-to: questions@xxxxxxxxxxxxx
- Dkim-signature: v=1; a=rsa-sha256; c=relaxed/simple; d=dons.net.au; s=default; t=1655442004; bh=I23mIAoamVkFEgG+blrVV9iWGAHlmkutgQH3QjO1Cek=; h=Subject:From:In-Reply-To:Date:References:To; b=IVMrGa4nY7xPOHPCJ3SpOMRJwVuCL1kUhy1fpaOa3kqHktF/Mec0g1CriwB39JvwT htgHV+khtUotsjsa4WUoHyhA82dhnJLNA2dZOEm6ORotN5SWQrUESxhLIDqGNHI+CU wtWitQuQ2O/GZ1j0SPUImTSSWB/VtxVXQdzY9zNQ=
- In-reply-to: <email@example.com>
- List-id: questions.lists.ntp.org
- List-unsubscribe: mailto:firstname.lastname@example.org
- References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com> <633A7397-0163-4408-BB2C-D639D6C5B92D@dons.net.au> <firstname.lastname@example.org>
- Reply-to: questions@xxxxxxxxxxxxx
> On 17 Jun 2022, at 12:52, Jim Pennino <jimp@xxxxxxxxxxxxxxxxx> wrote:
> Daniel O'Connor <darius@xxxxxxxxxxx> wrote:
>>> On 17 Jun 2022, at 00:07, David Taylor <email@example.com> wrote:
>>> On 16/06/2022 10:00, Thiebaud HUMBERT wrote:
>>>> To do the inversion, I just changed the "Pulse Mode" parameter to "Falling edge" from "Rising edge".
>>>> The offset induced by the "pulse length" has disappeared.
>>>> But there is still an offset of around 10.3ms, which I think is induced by USB as explained in this article about other chipsets (https://lists.freebsd.org/pipermail/freebsd-usb/2019- August/016078.html)
>>> Yes, Thiebaud, USB is not good enough for PPS signals!
>> This is absolutely false.
>> If you are using it for NTP then GPS+PPS over USB is quite adequate (from personal experience).
> As USB is a two wire interface, there is no such thing as PPS over USB.
The fact USB only has 2 data lines is irrelevant to wether you can send PPS over USB.
> You of course can get the ASCII data over USB, but to get a PPS signal
> you in general have to hack a USB GPS and add a signal wire for PPS then
> hack some interface on the computer to accept PPS.
This is absolutely not true in any meaningful sense.
> If all you need is accuracy in the 2 millisecond range, most recent USB
> GNSS dongles will achieve that without PPS.
You can easily do better than that with GPS/PPS over USB.
It is very easy to setup, readily accessible and cheaply done.
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum
This is questions@xxxxxxxxxxxxx