剛剛在 wikipedia 看來的, 其中有一段
As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a day-of-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19 TAI) on January 6 1980, and the week number became zero again for the first time at 23:59:47 UTC on August 21 1999 (00:00:19 TAI on August 22 1999). To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation message uses a 13-bit field, which only repeats every 8,192 weeks (157 years), thus lasting until year 2137 (157 years after GPS week zero).
算一算第一次 overflow 是在 1999 年 8 月 21 日, 第二次是剛好會在 2009 年 6/14 日嗎... 好像才一半??
看起來是 MStar 的 firmware (or IC) 為了省空間, 只拿 9 bit 來存, 到 512 之後就 overflow 了...
GPS 的時間應該會回到 1980 年代的時間... :p