[time-nuts] Re: Network interface cards that support timestamping

[Bob Camp]

Hi

Yet again, back to: what is the goal? 

For NTP, you have a range of numbers To a great degree they are limited by the network
nonsense that may (or may not) be going on. A 12ps NTP logging process likely does not 
do much for a network that has 12 ms of nonsense going on. 

PTP may / will / might / should fix some of that stuff. Unfortunately there is a “maybe” that 
qualifies all of that.

Welcome to the real world, all sorts of bad stuff happens. 

Bob 

> On Jan 30, 2023, at 6:18 PM, S McGrath via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Driving Pin1 only works with a ‘real’ serial port on a dedicated IRQ.  a
> USB interface will add unpredictable latency
> 
> On Mon, Jan 30, 2023 at 6:16 PM Lux, Jim via time-nuts <
> time-nuts at lists.febo.com> wrote:
> 
>> On 1/30/23 12:28 PM, S McGrath via time-nuts wrote:
>>> Most common way of getting 1PPS into a computer without a dedicated 1PPS
>>> interface is to drive a RS-232 port’s Carrier Detect pin (pin 1 on DB-9)
>>> with the 1PPS signal
>> 
>> 
>> 
>> back in the day when that tied directly to an interrupt with consistent
>> latency, that works pretty well.
>> 
>> 
>> These days, though, there's often USB hosts in the way, or some other
>> intermediate interfaces that increases the uncertainty in timing of
>> "when software does something" in response to "external event"
>> 
>> 
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