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Re: [gpsd-users] OT: Radio Module Time

From: George Sexton
Subject: Re: [gpsd-users] OT: Radio Module Time
Date: Tue, 9 Aug 2016 12:51:06 -0600
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

On 8/9/2016 11:11 AM, Mark Atwood wrote:
Hello George,

Have you considered sending your pull request for fixing the WWVB support for the Symtrik-RFT-60-LP WWVB to NTPsec?

That's an idea I really hadn't thought. If I'm getting it correctly, you're suggesting that I write an actual native NTP driver module. That would actually be very cool. I'd have to take a look at things though.

The clock module basically handles receiving and de-modulating the WWVB signal. It puts out a pulse every second which represents a bit, and the pulse width indicates whether it's a 1 or 0. For WWVB, 200ms is a binary 0, and 500ms is a binary 1, 800ms is a framing pulse.

So, the receiver code actually has to catch a whole minute of bits, and then decode the results into the current time/date. I briefly looked at the docs on writing your own reference clock driver, and there's one thing I'm not quite getting. To implement this kind of driver I would need to have a function called any time DCD changes state.

Is there some mechanism for doing that? I looked through the source for several reference clocks and couldn't quite make that out.

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Mark Atwood <address@hidden>

On Thu, Aug 4, 2016, at 09:52, George Sexton wrote:
This is a little off-topic, but there's a lot of overlap between the issues I'm having and GPSD, so I thought I'd ask here.
I've got a Symtrik-RFT-60-LP WWVB radio module that I bought online for like $15. I found the source code for linux on GitHub.
After fixing the WWVB support (doing the pull request is my next project), I tried to get it to work in PPS mode. I've found that the driver PPS support only works in serial port mode, not GPIO mode for a raspberry pi :(
I've thought about looking at the SHM code for GPSD and seeing if I could get some ideas on how to handle it. Alternatively, should I be looking at going the kernel module PPS route? Historically I've used GPSD for linux GPS/NTP, but I found this article:
and it was pretty easy to get going. The only issue I had was to get the PPS lock, I had to put in a time offset for the NMEA sentences. I made one stab at getting the NTPD .20 driver to work, but it's expecting NMEA and PPS to come out of the source so that's not going. I suppose one option would be to fake a GPRMC sentence and output it.
Any ideas on directions would be appreciated. I'm sort of interested in the radio because I want to see if I can get it working in my co-location server room (and I'm just kind of weird about time...). Funnily enough, my co-lo is in Fort Collins :)
Incidentally, I've just completed a Raspberry PI NTP server using a Garmin GPS16x-HVS and a custom interface board. I'm going to sell it on craigslist, but if anyone here is interested in a turnkey Pi/NTP system, contact me off-list.

George Sexton
MH Software, Inc.
Voice: 303 438 9585

George Sexton
MH Software, Inc.
Voice: 303 438 9585

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