[LinuxPPS] PPS ghost source? (fwd)

[K. Connolly]

Dear All,

Pardon the repeat message but I was not subscribed to the mailing list 
when I sent my last e-mail (below). I'm afraid I may have missed responses 
(if any). I am subscribed now and look forward to any helpful 
recommendations.

Cheers,

-Kevin

---------- Forwarded message ----------
Date: Wed, 8 Jul 2009 19:49:49 -0700 (PDT)
To: linuxpps at ml.enneenne.com
Subject: PPS ghost source?

Dear all,

First of all, thank you for the active development and thorough documentation 
-- it has been very useful as I am very new to NTP and LinuxPPS.

My current state: I followed the installation wiki and made it through with no 
errors and everything has gone smoothly. However, I am slightly perplexed 
because there seems to be a 1PPS signal whether or not I have my GPS device 
connected to the serial port or not. That is, with nothing connected to my 
computer I can run "./ppstest /dev/pps0" and get:

trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1247105841.815051558, sequence: 3323 - clear 0.000000000, 
sequence: 0
...etc

I look at /sys/call/pps/pps0/assert and it continues to increment. This is 
concerning, as I don't know whether or not the results I'm getting when I do 
attach my GPS device are coming from the GPS device or this mysterious ghost 
source.

I am very new to this, so I do not quite know what all information would be 
useful to provide. I used git to get the latest LinuxPPS source 
(2.6.28-rc6-20450-gace6faa). I defaultly had /dev/ttySX (X=0,3), and /dev/pps0 
present (I did not have multiple pps devices). The /sys/clas/pps/pps0 tree was 
also present. The only parts of the wiki install I did NOT follow was the 
issuing of "sudo modprobe 8250" command and the editing of the udev conf file. 
(By the way, it may be just because I'm a newb, but the ldattach command is a 
bit cryptic... What is the "18" signify?)

Thanks in advance for any advice and pointers, and my apologies if I've 
forgotten to include some crucial system information. Let me know and I'll try 
and respond with any necessary bits.

Cheers,

-Kevin