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Re: [questions] GPS+PPS vs NTP server, why a huge offset ?
> On 19 Jun 2022, at 19:27, David Woolley <firstname.lastname@example.org> wrote:
> On 19/06/2022 07:38, Daniel O'Connor wrote:
>>> OK, then to which of the USB connector pins do you connect the PPS
>>> signal to get "PPS over USB"?
>> You can connect them to CTS or RTS, on FreeBSD these can then hook into the kernel PPS API.
>> It works very well in practise, especially for the cost & effort required.
> Taking the other side for this one, which of Ground, D+, D-, and VBus have alternative names of CTS and RTS? (I guess I should add StdA_SSRX-, StdA_SSRX+, StdA_SSTX+, and StdA_SSTX-, for USB 3.0, compatibility.)
None of course, but how do you think the CPU gets to know when a PPS edge appears on a 16550?
It is not magically wired into it, an IRQ is generated and has to be serviced before a timestamp can be taken. The bus it is on (LPC) is not designed for low latency and is not directly connected to the CPU..
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum
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