[time-nuts] Re: Ryzen mobos with serial port for Garmin GPS?

[Alec Teal]

Sorry I've replied to this message but I didn't include some knowledge 
thinking it was implicit:


No PC has had a true serial port for years. Probably decades. For a very 
long time "this stuff" (ISA slots, which are basically a bus for a 
really old processor - that guy I mentioned in the other message knows 
more and I'm happy to ferry questions if you like) has been done by 
"superIO" chips and suchlike. It's not been a direct interface to the 
processor probably for a good 20 years.


Any "serial ports" you have will be over PCI anyway (which may or may 
not be PCIe - this doesn't really matter) - you'll want to make sure 
it's not behind a bridge though.


It's worth remembering that crap being pushed out of the cache will 
cause significant variance, this is well known in ethernet circles as 
getting something to deal with 10gbit/sec ethernet is non-trivial. There 
are things like DMA'ing right to the cache.


So RE: the serial port - that ship has sailed, but I'd be curious to see 
a USB and a PCIe one compared for example.


Alec

On 05/11/2021 05:36, Rich Wales wrote:
> Looking to design my next Linux (Ubuntu) system, built around a Ryzen 
> processor.
>
> In previous systems, I've had great success using a Garmin GPS 18x 
> unit (small hockey puck with a wire tail) hooked up to a DB9 serial 
> (COM) port on the motherboard, to provide a local (stratum-0) time 
> reference via gpsd and chronyd.  However, mobos with a serial port are 
> becoming harder to find.
>
> (Yes, I know that PCI serial port cards exist -- however, these are 
> not suitable for connecting a GPS time reference because the PPS 
> signal timing is unpredictable -- so I've limited myself to using 
> motherboards with a builtin serial port.)
>
> What Ryzen (Socket AM4) motherboards have worked out well for people 
> who want to do what I'm proposing?
>
> Alternatively, can anyone recommend a better hardware solution than a 
> Garmin GPS attached via a serial port?
>
> Thanks for any suggestions.
>
> *Rich Wales*
> richw at richw.org
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