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From: | Mike Tubby |
Subject: | Re: [gpsd-users] Maybe beating a dead horse: Week number rollover |
Date: | Fri, 9 Nov 2018 16:35:03 +0000 |
User-agent: | Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
Adam, I can't speak for GPSD per-se but we have a number of products based on older Trimble GPS receivers (SV6, ACE-II, ACE-III and Lassen-iQ) that are used both with our own applications and with NTP using Trimble TSIP binary. The older GPS receivers reported the week number in the range 0-1024 and wrapped back to zero as per the air-interface description (NavStar ICD-GPS-200) in August 1999 and will presumably do the same thing again this time. These were fixed, last time, by doing: if (week_number < 990) week_number += 1024; in various drivers. This hack is also in the Trimple RefClock driver in NTP. When we test the oldest receivers with a simulation we built using a HackRF we do see them jump back 19 years as expected. The ACE-III documents support for 'Extended Week Number' and states that it is good to 2017, however have find it correct beyond the April 2019 WRNO. The Lassen-iQ is also documented as supporting extended week number but claims to be good to 2024. I expect that Trimble have been addressing this issue by using a date/constant based on when the firmware was built or some other trick to ensure that week number only ever goes forward, thereby masking the problem. YMMV. Mike On 11/9/2018 2:09 PM, Adam Heller
wrote:
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