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Instrument panel trips question

Discussion in 'Model S' started by fasteddie7, Nov 28, 2016.

  1. fasteddie7

    fasteddie7 Member

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    this has probably been answered somewhere but I can't seem to find it, maybe I'm not searching for the right terms. What is the negative number over minutes mean on the trips portion on the instrument panel? I've included a photo of said negative minutes. 820FD360-0A35-47BF-ABFB-0D08AB5211EE.JPG
     
  2. Brass Guy

    Brass Guy Member

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    You must've got the flux capacitor option!

    I've never seen that. Typically in programming, if you get an unexpected negative number it means the programmer used a data type that is too small to handle the number encountered. For example, a byte may contain a value from 0 to 255, or a signed value from -128 to 127. If you have a signed byte value at 127 and add 1, the value will display -128.
    That's what it looks like to me, an overflow.
     
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  3. SomeJoe7777

    SomeJoe7777 Marginally-Known Member

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    Agreed, this looks to be a programming error. That top line is supposed to show miles and minutes since the car was last powered on, and it shows -8 minutes and 4034 miles.

    Let me ask this question: Between the time the car was powered on and the time you took this picture, was there a time change (i.e. change from daylight time to standard time, or change of time zone traveling west)? This could possibly account for the display.

    For the programmers among us, think of the following scenario:

    - Car powers up at 1:00 PM.
    - Car drives due west at 72 MPH.
    - At 1:52 PM, car changes time zone to next western time zone, time of day becomes 12:52 PM.

    Computation of number of minutes car has been powered on: 1:00PM - 12:52PM = -8 minutes.
    Computation of miles driven: Actual miles incremented on the odometer = 72 / (52/60) = 62 miles. Car carries sign from time over to actual miles driven, so car thinks actual miles driven = -62 miles.

    -62 miles displays as 4034 miles if the miles are stored as a 12 bit unsigned integer.

    This is only my speculation, and I'm not saying this is what's happened here. This is just one guess that happens to explain the display shown.
     
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  4. fasteddie7

    fasteddie7 Member

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    There was a time change when daylight savings time changed. It still does this daily. It always goes negative when I start driving. So odd.
     
  5. bmah

    bmah Obscure Member

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    Interesting analysis.

    The best current practice for timekeeping, at least for myself and all the software engineers I work with, is to maintain time in seconds (maybe milliseconds or microseconds if appropriate) since an absolute epoch time, doing all calculations in those units, and then only converting to the local timezone when displaying absolute times. That avoids (almost) all problems with crossing timezone boundaries and daylight savings time transitions. That's pretty much the standard for most UNIX and/or Internet programs.

    That having been said, I have no idea how the Tesla software stack keeps track of time internally or what might have caused this, so...???...

    Bruce.
     
  6. Brass Guy

    Brass Guy Member

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    It does this all the time? I was thinking it was a one time deal. I think you need a software refresh. Definitely contact a service center about this, it is not normal operation.

    I drove across the country (and back!) this summer, and I had no issues driving across time zones. I used the "elapsed time" and "miles driven" to log legs of the trip.
     
  7. Snerruc

    Snerruc Member

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    I get the same thing all the time with one of the trip meters. No time zone changes ever where I live.
     
  8. fasteddie7

    fasteddie7 Member

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    I start every trip at -59 and it counts down to 0. Crazy. It didn't really bother me though. Maybe a future software update will fix it.
     
  9. Brass Guy

    Brass Guy Member

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    Out of curiosity, what does "miles" start at and does it increase from there? It doesn't affect your odometer or you'd be over 100k miles by now.

    I'd assume when minutes gets to 0 it goes positive if you keep driving.
     
  10. fasteddie7

    fasteddie7 Member

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    Miles start at 0. Yes, after time hits 0 it starts counting up.
     
  11. bmah

    bmah Obscure Member

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    @fasteddie7: just for posterity, what software version(s)?

    Bruce.
     
  12. Brass Guy

    Brass Guy Member

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    I was asking because next to the -8 minutes I see you've driven 4034 miles in 51 minutes.
     
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  13. MDMGSO47

    MDMGSO47 Member

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    I think I have it figured out. You have the new Model S P500D prototype. Your battery can produce 1.21 gigawatts that can do 4034 miles in 51 minutes. In fact, you are going so fast that you have traveled back in time 8 minutes, hence -8. .

    Elementary, Dr. Brown.
     
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  14. fasteddie7

    fasteddie7 Member

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    the miles never change, they are always the same. I guess I could factory reset but then I might have to re set up everything and re-enable the app for remote access, re-teach the parking sensors and autopilot, and set up my podcasts. It doesn't seem worth it to me, I really only use the info on the bottom half which seems to display accurately.
     

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