GPS Date

[Steve Graves]

Hi Caleb,
I believe I have conquered the angles. Now I am trying to generate Time Stamps. The data I get from the DREG_GPS_DATE register is 0x497050c0. That doesn’t fit the datasheet description. In fact, one can’t fit the year into a byte, so I am missing some information about this register. Can you shed some light on the format for this register?

Thanks,
Steve

BTW The DREG_GPS_TIME appears to be the seconds since midnight (Universal Time). Is this correct?

[CalebModerator]

Hi Steve,

You are correct, all time register report the time in seconds since midnight. But it is GPS time, not UTC time (they’ll be different by a few seconds, I believe).

The high-order byte in the GPS date register should be 0, so something is definitely going on. The year format, however, is a two-digit year format so that it can be represented by a single byte. 15 == 2015. So there is nothing wrong with that.

For operation today (5/12/2015), the contents of the date register *should be 0x000F050C. I connected a GP9 and found that the GPS date data is not correct. We upgraded to a new GPS module prior to release, and while the functionality of all other critical GPS features was validated (position, timing, etc.) the GPS date outputs must have changed. This will require a firmware update to fix. In the mean-time, it looks like the GPS date isn’t going to be available.

[Steve Graves]

Hi Caleb,
More information about DREG_GPS_DATE. At UTC midnight the raw value went from 0x497050c0 to 0x497050d0. If I take the data sheet as a guide and assume some kind of error. It looks to me like the nibbles are swapped for day and month. If we flip them we get 5 12 to 5 13 as the Month Day which fits going from May 12th to May 13th. The year is still a mystery. I have learned all about GPS time and GPS weeks (from 0:00 Sun 6 Jan 1980) and week seconds. I haven’t be able to relate that data to the year either. I am giving up on this for now and hope that you can enlighten me.

Thanks,
Steve

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