[time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

Gary E. Miller gem at rellim.com
Mon Feb 13 15:15:26 EST 2017

Yo Ruslan!

On Mon, 13 Feb 2017 11:07:49 -0500
Ruslan Nabioullin <rnabioullin at gmail.com> wrote:

> Hi, generally speaking, what are the performance differences between
> the following: 1. direct RS-232 (i.e., what I believe is a standard
> PCI card offering RS-232---essentially UARTs interfaced more-or-less
> directly to the PCI bus); 2. RS-232 via USB; 3. PPS decoding PCI
> cards (which might also have an IRIG input or even an onboard GNSS
> receiver).

#2 will have a lot higher jitter than #1.  On a #2 you can expect
500 micro second best timing.  On a #1 you can get to 1 micro second.

On a RasPi using GPIO you can get to 500 nano second.  Data
available on request, but better on the devel at ntpsec.org list.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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