[time-nuts] PCI-E Serial Card For Windows NTP?

Ed Armstrong eds_equipment at verizon.net
Thu Jun 25 06:41:06 UTC 2015

Hi, I'm still pursuing setting up a fairly accurate NTP server connected 
to my Nortel/Trimble GPSTM. So far I've been playing with a Raspberry Pi 
2, and have made fairly good progress using a bunch of tweaks detailed 
by another member of this list. However, it has been noted that the 
Raspberry Pi has some limitations for this purpose, not the least of 
which is having a USB connected ethernet port. Consequently I am also 
looking at some other options.

The GPSTM and the Raspberry Pi will be sharing a shelf with my server, 
which is running a Core i7-3770 @ 3.4Ghz and a 64-bit version of Windows 
7 Ultimate. This machine is typically running at about 10 to 20% CPU 
usage, and it is extremely rare for the CPU usage to exceed 50%. It is 
also equipped with an Intel gigabit ethernet port, connected by PCI 
express bus. I expect this may perform a little better than the pi's 
100Mb card which is connected by USB. I also suspect that the i7 will do 
a bit better in terms of interrupt latency.

There is a driver available for Windows 7 which allows use of the DCD 
pin on a serial port for PPS. Sadly, this machines motherboard does not 
have a serial port, nor a parallel port. Not even a header for one. And 
this leads to my question.

I am considering adding a PCI express serial port card to this machine, 
but I don't know how well they perform for this application. There are 
quite a few different cards available, ranging in cost from under $10 to 
over $50. I am wondering how well these cards work for this application 
in general, and if there are some cards which will work well and some 
which will work poorly or not at all. And of course, if there is major 
variation between the cards, I would like to know how to pick one which 
will work well. I do have a little experience with parallel port add on 
cards, as I run a CNC milling machine which uses the parallel port to 
control the machine. Most of the parallel add-on card you can buy work 
fine for a printer, but will not work at all for sending pulses to the 
CNC machine. Only a very few cards are full function parallel ports, and 
they are pricey. Before I waste $8 on a cheap serial port card, I want 
to make sure I'm not looking at the same situation. If it matters, I'm 
planning on a dual-port card.


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