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--- doc:appunti:hardware:gps_logger_i_blue_747 [2010/04/03 11:45] – niccolo
+++ doc:appunti:hardware:gps_logger_i_blue_747 [2019/10/11 17:47] (current) – [Week Rollover Bug] niccolo
@@ Line 65: / Line 65: @@
 If you encounter some problems, please run the program with the ''**-d 7**'' option and write me a mail with the output. You will find my address in the program itself.
-==== Credits ====
+===== Weeks Rollover Bug =====
+It turned out that several GPS based on the MTK chipset are affected by a **Weeks Rollover Bug**. You discover that your device is affected by the bug because the GPX files you save from it, will have a **timestamp badly in the past**.
+Actually I have two i-Blue 747 GPS data loggers. The older one is a **Model ID 001B**, which has already manifested the problem: today is **2019-10-10**, but GPX points logged have a timestamp of **2000-02-24**. If you do the math, you can find that there is a **difference of exactly 1024 weeks**. This means that the device internally stores timestamps using a **weeks counter of only 10 bits**. So exactly 1024 weeks after its //EPOCH// (the begin of the time it can handle), the timestamps rolls-back of that amount of time.
+The other logger of mine is a **Model ID 001D**, which instead is still recording correct timestamps today. I suspect that the weeks counter is nevertheless 10 bits, and just the hard-coded EPOCH is more recent. So the bug is **just to come in the near future**.
+  * **[[https://www.theverge.com/2019/3/8/18255847/gps-week-rollover-issue-2019-garmin-tomtom-devices-affected|Older GPS devices are facing their own mini Y2K bug next month]]**
+  * **[[https://github.com/gpsbabel/gpsbabel/issues/349|Holux M-241 gps weeks rollover issue]]**
+===== Credits =====
 I wish to thank all the people behind the **[[http://sourceforge.net/projects/bt747/|BT747 project]]**: everything I made is derived from their work.