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

Trevor N. qb4 at comcast.net
Tue Feb 21 21:50:25 EST 2017

On Tue, 21 Feb 2017 07:37:34 -0500, BC wrote:
>Some 1588 chip sets have (or had, I haven’t looked recently) external sync pins. 
>This does get into the whole, what’s a motherboard / what’s a peripheral 
>debate. Plugging in a 1588 card to get that pin probably no longer counts
>as a simple solution. If plugging in a card *does* count then that opens up 
>a lot of possible options. 

I found while looking at the datasheets for newer Intel server
ethernet cards that they have the ability to timestamp GPIO pin
transitions, but none of them have their internal timebase
synchronized to a counter in the CPU. It looks like they are clocked
from a separate XO on the card.  Maybe if it was synchronized to the
PCIe clock / BCLK  they could take advantage of that new Always
Running Timer in Skylake processors.  I'm surprised that Intel hasn't
made a big deal about it. Support for it was added in the Linux e1000e
driver early last year.

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