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

[Angus]

Although I didn't buy any of them for timing, I did make sure that
they were based on a 16550 UART since a lot of legacy hardware and
software expects that. Startech emphasizes the 16550 and no bridge,
but they are not cheap and I'm not convinced that they're worth it.
Mine were just cheaper 2 to 6 port ones, although it is possible to go
too cheap!


On Fri, 5 Nov 2021 19:14:55 -0700, you wrote:

>Angus wrote:
>> /What timing issues did you have? I've used a similar setup on two old 
>> windows machines (one XP and one Win10) and I didn't see much 
>> difference between the built in serial port and the ones on the PCI 
>> serial cards. They were not PCIe./
>
>The serial card I used (with unpredictable PPS signal timing) was a PCIe 
>card.  But I think the more significant difference was that this PCIe 
>serial card was really a USB card with a serial-to-USB front end, and 
>this protocol conversion was the reason for the extra jitter.
>
>Old PCI serial cards came from a time before USB was common (or even 
>existed), and they sent the serial data directly to the PCI bus without 
>going through any intermediate steps.  If we could find PCI or PCIe 
>serial cards which worked in this same way, we would presumably have the 
>same high performance as in the old days. However, there is very little 
>incentive nowadays for hardware manufacturers to do this; the few serial 
>cards that are still made today (after all, who really needs, wants, or 
>even knows about RS232 anymore?) generally cut corners by slapping a 
>cheap serial-to-USB front end onto a cheap USB card, and except for 
>those of us who really need accurate timing, none of their customers are 
>likely to care or even notice.
>
>*Rich Wales*
>richw at richw.org
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