[time-nuts] WWVB PPS clock pulse ?

[Magnus Danielson]

On 03/30/2011 06:58 AM, Chris Albertson wrote:
> On Tue, Mar 29, 2011 at 7:30 PM, Lenny Story<lenny at codematic.com>  wrote:
>> All,
>>
>> Ok... so i'll just make it a rising edge pulse of ~500ms.  That should be
>> enough time for a linux box to detect it.
>
> I would vote for a non-symetric waveform so you can see if it is inverted.

I've found 200 ms high, 800 ms low quite useful for scopes. :)

For other signals I do just 50% and it works well, but sometimes you can 
see reversed polarity and you have to spend time to figure out if it is 
inverted or not. Wastes a lot of time.

> I don't think the pulse is detected by software.  It's an interrupt.
> The Linux PPS handler reads the clock and stores it.  Latter software
> that "reads" the PPS is given the stored time tag. I'm pretty sure the
> interrupt hardware is trigged by the edge.  Choose the length so a
> human (you) can detect it
>

Agree.

Cheers,
Magnus