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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 [2019/10/10 22:47] – [Week Rollover Bug] niccolo
@@ Line 1: / Line 1: @@
 ====== MTKBabel ======
-:!: **NEW!** MTKBabel is now hosted on **[[https://sourceforge.net/projects/mtkbabel|Sourceforge]]**!
+MTKBabel is hosted on **[[https://sourceforge.net/projects/mtkbabel|Sourceforge]]**!
 **MTKBabel** is a Perl program to operate the **i-Blue 747 GPS data logger**. It should work also with other GPS devices based on the **MediaTek MTK** chipset. Starting with version **0.7** it offers also support for the **Holux M-241** data logger. It is free software released under the GPL license.
@@ 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 ====
+===== Week Rollover Bug =====
+It turned out that several GPS based on the MTK chipset are affected by a **Week 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 **week 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 week 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**.
+===== 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.