>> Now using the following ntp.conf I can see that things are working,
but not as expected. I would expect the pps clock to take over, no
matter what happens, since I understand it is either there or not and it
can't be wrong. Instead my system randomly marks either of these a false
ticker every now and then..
>
> Actually the pps CAN have noise on the line. I have found with my Garmin
> 18LVM that sometimes the interrupt fires of 6 or 7 hits in a few
> milliseconds,-- some sort of line noise coming in. Now, it is I admit
a bit
> of a kludge and I have not bothered to track down the problem-- bad
solder
> joint, TV interference,.....-- but it happens.
> What is best if you can record say a days worth of interrupt timings
> without haing the pps discipline your clock, and look at, or rather
plot (
> since looking at 86400 entries is liable to fry your brain) to see if you
> are getting glitches-- noise tends to occur randomly so plotting
> t_{i+1}-t_i over the day will show you if glitches have occured. If they
> differ from 1 second according to your computer clock ( and you have left
> your computer clock just rinning and not resetting it suddenly-- even ntp
> running on the outside sources is fine since it shifts the time slowly)
> then you have noise.
Ok, I will, I am just not sure, how to do so. Here are some assumptions,
please correct me, where I'm wrong:
cat /proc/interrupt shows me /counts/ of different interrupts, so I
assume,that is not what I am looking for. There is a IO-APIC-edge timer
interrupt (0) and a IO-APIC edge serial interrupt (4). The timer
interrupt grows constantly and the serial grows a couple of thousands
every start of a second (looks like) and If then stops until the next
second. I assume that's the one and that the interrupts are fired, als
long as the pps-signal is incoming.
Now I find cat /proc/irq/4/serial to reportI "Is a directory" and I find
nothing in there, so I am a bit stuck, since I simply don't know what to
record..
> Note that serial port nmea is liable to be out by up to 1/2 sec and
to have
> a lot ( 10s of msec) jitter on it, since the end of the string
received by
> a slow serial port ( eg at 4800Bd, it takes an nmea sentence of about 60
> characters 1/8 of a second to be delivered and will have a jitter of few
> characters in length-- or about 10ms jitter)
I don't understand why you are mentioning this, maybe you got me wrong.
I run the nmea gps over usb and the pps goes to the serial port. So
there is no data exept for the pps on my serial line..
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