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fizzymagic

Week Number overflow

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I thought about posting this in the GPS forum, but I think it is of more general interest.  Today I had a problem with my field notes.  They all had a date of March 11, 1999.  Turns out this is a case of my particular GPS model (Delorme PN-60) experiencing the week number overflow a little early. For the next 1024 weeks, my GPS will give the wrong date.  The base date they apparently used in the firmware is in March of 1999.

 

Here's a quick description of the issue:  the GPS satellites send the current date to you GPS using a week number since Jan 6 1980.  They only allocated 10 bits for it, though, so 1024 weeks from then (in August 1999) it overflowed for the first time. The next overflow is due in April 2019, when everyone's GPS will start showing the wrong date unless the GPS manufacturer put in some way to accommodate the overflow.  Mine just overflowed about 6 months early for no particularly good reason.  But it will happen to everyone, especially those with older GPS units.

 

Is anyone else with a Delorme seeing the same thing?  It's easy enough to fix (I wrote myself a little Python script to add 7168 days = 7 * 1024 weeks to the date for each field note) but it is annoying in a minor way.  Maybe we can convince Garmin to fix it!

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Hmm... Interesting.  It's like Y2K all over again.

I wonder if anyone can find out specific models that would be affected (or, possibly easier, which models AREN'T affected).  (For example, we have a vested interest in Oregon 650t's working properly.)

 

It sounds like the dates will just cycle through the same 19+ year range unless they update the base date in the firmware (or made some other accommodation, as you pointed out).

(It's too early for me to write a program to model this, but it sounds as if, with only 10 bits, you're limited to 1023 weeks from whatever the base week is and this will constantly reset to 0 whenever it rolls over into the 11th bit.)

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Thanks for the explanation. I had been wondering what was up with my Delorme's date since I knew it received the date from the satellites - I just didn't realize how it was being sent and interpreted.

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I have the same issue on my PN-60w.  I noticed it when I downloaded my recent tracks which are defined by date they are all the same date such as 1999-03-10, XXXXXX.gpx.  With Field Notes I use a text editor to correct the dates prior to downloading because Geocache will not recognize old dated Notes.

 

I went to Garmin's "Migrating from old Delorme Forum" looking for an answer but none posted.

 

Of more concern to me is how will the affect my inReach messages.  I have the older model transceiver paired to my PN.  Sent a message to myself and it wasn't received.  Garmin.inreach could not help with legacy inReach and recommended sending a email to support@delorme.com which I did.  Now I wait.

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10 hours ago, fizzymagic said:

I thought about posting this in the GPS forum, but I think it is of more general interest.  Today I had a problem with my field notes.  They all had a date of March 11, 1999.  Turns out this is a case of my particular GPS model (Delorme PN-60) experiencing the week number overflow a little early. For the next 1024 weeks, my GPS will give the wrong date.  The base date they apparently used in the firmware is in March of 1999.

 

Here's a quick description of the issue:  the GPS satellites send the current date to you GPS using a week number since Jan 6 1980.  They only allocated 10 bits for it, though, so 1024 weeks from then (in August 1999) it overflowed for the first time. The next overflow is due in April 2019, when everyone's GPS will start showing the wrong date unless the GPS manufacturer put in some way to accommodate the overflow.  Mine just overflowed about 6 months early for no particularly good reason.  But it will happen to everyone, especially those with older GPS units.

 

Is anyone else with a Delorme seeing the same thing?  It's easy enough to fix (I wrote myself a little Python script to add 7168 days = 7 * 1024 weeks to the date for each field note) but it is annoying in a minor way.  Maybe we can convince Garmin to fix it!

 

I envisioned someone of your geocaching stature using a top of the line Garmin. Thanks for ruining that image ;-)

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4 hours ago, bflentje said:

 

I envisioned someone of your geocaching stature using a top of the line Garmin. Thanks for ruining that image ;-)

 

Garmin units are overpriced by about a factor of 2 and I don't like the UI.  But I may end up with one in the next year....

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I contacted support@Delorme.com about the 1999 problem and here is their reply.

 

Hello Robert
Thank you for contacting Garmin Product Support and I apologize for the issue experienced with your DeLorme PN-Series GPS device.
Due to how the device uses Global Positioning Satellites to set its own time and how technology changes rapidly over the years, the PN-Series GPS will unfortunately no longer display the current correct time.  We sincerely apologize for this inconvenience.
At this point; due to the number of improvements and the plethora of additional features and functions, we would recommend upgrading to a newer Garmin Handheld GPS.  Please review the links below for some models comparable to your older DeLorme PN-Series GPS.

InReach Explorer + – Maps with premium satellite communications.
https://buy.garmin.com/en-US/US/p/561269/pn/010-01735-10#
 

GPSMap 66S – Premium rugged (MIL-STD-810G) handheld GPS. 
https://buy.garmin.com/en-US/US/p/598408/pn/010-01918-10#overview
 

Instinct (It’s MORE than just a watch!…and as a wearable…it can always be on you…surf, hike, train and work…it’s the ultimate tool for its price point)
https://buy.garmin.com/en-US/US/p/621802

Again, I apologize for the issue with your PN-Series GPS and hope with the overabundance of high-end rugged GPS devices Garmin  provides, something will fulfill your navigation needs.
Your older inReach does not need to Sync.  Those older devices only did a Sync to update firmware and you have the latest for that older device.
Please let us know if you have additional questions or concerns. 
Regards,
Kurt Ringrose
Product Support, Garmin Outdoor (inReach)
Garmin International
http://support.garmin.com


The GPSMap 66S will be available in 5-8 weeks and costs $449.99.  The inReach Explorer + costs $449.99.

It will cost me $900.00 + shipping to duplicate what I have now.

 



CONFIDENTIALITY NOTICE: This email and any attachments are for the sole use of the intended recipient(s) and contain information that may be Garmin confidential and/or Garmin legally privileged. If you have received this email in error, please notify the sender by reply email and delete the message. Any disclosure, copying, distribution or use of this communication (including attachments) by someone other than the intended recipient is prohibited. Thank you.

 

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48 minutes ago, Capt. Bob said:

I contacted support@Delorme.com about the 1999 problem and here is their reply.

Shoot. I was so hoping the answer would be, "We're not going to do anything about it, but here's the code for the firmware. Have at!" There are so many reasons I keep hoping they'll let the code loose, and I thought this might make the difference. I don't suppose anyone has stolen the source code and wants to slip me a copy? I'll make it worth your while if I can produce a fix.

 

When I noticed the date go bad on my PN-60w, I figured it was some kind of roll over fail. I don't use field notes, so fixing them up wouldn't do me any good, but the bad date still causes me two problems. First, obviously, is that the GPSr no longer tells me what date I should put in the logs I'm signing. It's really annoying to have to pull out my cell phone at every cache. The second problem -- where I actually saw the bug first -- is that it means the dates on PQ files are wrong. I usually note how old a PQ is when I replace it with a newer one just to see how fresh I'm keeping different areas, so I was quite startled when windows asked me whether I really wanted to copy the new PQ or would I rather keep the old one from March, 1999.

 

For some reason I didn't notice this conversation until now. I'll check my PN-40 when I get home just to confirm, but since it uses the same firmware, I assume it has the same problem.

 

After geocaching with a cracked screen for a few years now, I always assumed that physical failure would be my PN-60's ultimate demise, so it's both amusing and sad that what's really going to force me to switch to one of those less desirable units is a software bug.

Edited by dprovan
was "big", should have been "bug".

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4 hours ago, Capt. Bob said:

The GPSMap 66S will be available in 5-8 weeks and costs $449.99.  The inReach Explorer + costs $449.99.

It will cost me $900.00 + shipping to duplicate what I have now.

 

Bummer about the cost. If you're primarily planning to use the inReach as a satellite messenger (not for navigation), you might see if the inReach Mini would work for you. It's slightly less expensive.

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I am beginning to see other problems with the PN-60w that seem to be getting worse.  It now takes a long time to acquire satellites which implies the almanac data isn't being read properly.  Also the ephemeris data must be affected because once satellites have been acquired the EPE varies wildly over time.

(solved the problem with a NVM reboot)

 
It's a shame that Garmin/Delorme won't undertake revising the firmware to correct the date issue.  It's irresponsible of them to not notify users of the problem particularly those users, like me, who are paired to inReach.  It could be a life threatening situation.  I suppose somewhere in their multi-paged legal agreement they are absolved of any liabilities so they don't care.

Edited by Capt. Bob
Update results

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While I am unhappy that Garmin won't even let us fix our own firmware, concerns about ephemeris and almanac data should not be issues.  My PN-60 is still acquiring the satellites just fine and the accuracy also seems fine.

 

I kind of don't want to reward Garmin for their bad customer service by buying a handheld from them.

  • Upvote 1

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11 hours ago, fizzymagic said:

I kind of don't want to reward Garmin for their bad customer service by buying a handheld from them.

Let me know what alternative you find...

 

But to be fair, while Garmin obviously wanted to get the old PN GPSrs out of the picture as quickly as possible, DeLorme had given up on the PN's long before that. It's not as if they were still supporting the firmware even before Garmin bought them. They could have published the code, just as well.

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It's not just DeLorme items that are affected. I have a Garmin Etrex Venture HC, and this started to show an incorrect date a couple of weeks ago. I phoned Garmin, they told me I wasn't the first to report this trouble recently, and they were working on a solution.

 

The issue is clearly related to the week number in the GPS data. 21st October 2018 was exactly 7000 days (1000 weeks) after the last week number rollover on 21st/22nd August 1999. Thus it looks like the unit software cannot handle GPS data week numbers larger than 3 decimal digits.

 

Given this problem, I suppose there is little chance of the device dealing gracefully with the week number rollover coming on 6th/7th April 2019. I remember back in August 1999 I had a Garmin 'handheld' GPS, and to cope with the rollover it required a hard hard reset, then a considerable period to gather data until it was working again. Anxious moments...  

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I'd like to find a replacement for my PN-60W and inReach but don't know if there is anything comparable.  Upset the PN-60W was discontinued but I guess I can't blame DeLorme. Perhaps they weren't selling enough units to keep market share and that is why they got bought out?  In the meantime I wrote a simple formula in excel and convert before I post. Just add 7168 to the date displayed and you'll have your post date.  You can change manually or just edit the field note.txt file.

 

3/27/1999 11/10/2018     7,168.00
     
GPS Date: 3/27/1999 11/10/18

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