st599
Well-known member
You're assuming that hte processor is using 8bit Bytes. Some specialist processors still use different Bytes.
Government safety warning, Furuno gps.
- Thread starter Clancy Moped
- Start date
You're assuming that hte processor is using 8bit Bytes. Some specialist processors still use different Bytes.
mjcoon
Well-known member
I think in this case it is not storage in the device that is the limitation but transmission bandwidth. The satellites are transmitting not only the packets of data (maybe "date" was a Freudian slip!) that allow triangulation of location, but also, over longer timescales, updates to the orbits of all the satellites to provide the essential "baseline".
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justanothersailboat
Active member
st599... very good point I didn't even think of because I'm not in those specialist areas 
I wonder whether this is becoming less common or not...
mjcoon... true that the transmission of updated satellite position tables / ephemerides (if I can even spell that) is piggybacked on the clock signals and is really slow. I think it's in the tens of bits per second. I'm not really sure but it appears to have been consistent over a long time and it's what devices do with it that can allow quirks to creep in. My boat GPS seems to have coped with the cumulative updates since the 90s apart from that one weird thing about the time. I am pretty sure my old handheld has not coped with those updates and that's why it goes on the fritz in such a predictable, regular manner.
I wonder whether this is becoming less common or not...mjcoon... true that the transmission of updated satellite position tables / ephemerides (if I can even spell that) is piggybacked on the clock signals and is really slow. I think it's in the tens of bits per second. I'm not really sure but it appears to have been consistent over a long time and it's what devices do with it that can allow quirks to creep in. My boat GPS seems to have coped with the cumulative updates since the 90s apart from that one weird thing about the time. I am pretty sure my old handheld has not coped with those updates and that's why it goes on the fritz in such a predictable, regular manner.
robmcg
Well-known member
This was the reply I had from a Furuno field engineer. This was back at the end of 2016 ?
Many thanks for your email help request and I have been tasked with trying to assist you with your recent enquiry.
I am afraid that the unit has suffered from what is known as GPS roll over and is potentially at the end of its life, I have tried to explain this in greater detail below which you will hopefully understand.
The GPS week number count is reset every 1024 weeks which roughly equates to 19.6 years. Time of the week count and GPS week number count make up a total of 29-bits, 19 of the least significant bits are for the TOW (time of week) count and the remaining 10 bits are for the week number count. The 10 bits for the week in number format count up as 1,2,4,8,16,32,64,128,256,512, *10 bits can only count to 1023 before rolling over, adding all the previous numbers listed (1-512) will add to 1023 and at this point the chip will roll over and reset. After rolling over depending on programming the unit may suffer consequences but never really sure until they happen, have placed some examples below:
• It may revert back to a date programmed into its memory (EEPROM) or simply revert back 19.6 years in time to the start all over again from the beginning.
• It may sense an error and refuse to calculate a position all together.
• It may display incorrect positions as they incorrectly determine the position of the satellites from the ephemeris transmitted inside the navigation message, ephemeris = a table or data file giving the calculated positions of a celestial object at regular intervals throughout a period of time.
In this instance it looks like the unit has wound itself back 19.6 years to original program date/time, you can wait a couple of weeks to see if this sorts itself out but I don’t think it will and unfortunately there is no fix other than to purchase a new unit such as the GP-32.
If you decide to live with the date being incorrect then I would however check the positional accuracy of the equipment now just in case it is calculating an incorrect position.
Please see the link below for a list of UK dealers so you can find the one relevant/closest to your location should you wish to enquire about purchasing a new unit, The GP39 is the same physical size as your GP-30 with the addition of a colour display:
http://www.furuno.co.uk/dealers.php5
If you feel we can be of any further assistance then please ask and I will endeavour to try my best and answer any questions that you may have.
Many thanks for your email help request and I have been tasked with trying to assist you with your recent enquiry.
I am afraid that the unit has suffered from what is known as GPS roll over and is potentially at the end of its life, I have tried to explain this in greater detail below which you will hopefully understand.
The GPS week number count is reset every 1024 weeks which roughly equates to 19.6 years. Time of the week count and GPS week number count make up a total of 29-bits, 19 of the least significant bits are for the TOW (time of week) count and the remaining 10 bits are for the week number count. The 10 bits for the week in number format count up as 1,2,4,8,16,32,64,128,256,512, *10 bits can only count to 1023 before rolling over, adding all the previous numbers listed (1-512) will add to 1023 and at this point the chip will roll over and reset. After rolling over depending on programming the unit may suffer consequences but never really sure until they happen, have placed some examples below:
• It may revert back to a date programmed into its memory (EEPROM) or simply revert back 19.6 years in time to the start all over again from the beginning.
• It may sense an error and refuse to calculate a position all together.
• It may display incorrect positions as they incorrectly determine the position of the satellites from the ephemeris transmitted inside the navigation message, ephemeris = a table or data file giving the calculated positions of a celestial object at regular intervals throughout a period of time.
In this instance it looks like the unit has wound itself back 19.6 years to original program date/time, you can wait a couple of weeks to see if this sorts itself out but I don’t think it will and unfortunately there is no fix other than to purchase a new unit such as the GP-32.
If you decide to live with the date being incorrect then I would however check the positional accuracy of the equipment now just in case it is calculating an incorrect position.
Please see the link below for a list of UK dealers so you can find the one relevant/closest to your location should you wish to enquire about purchasing a new unit, The GP39 is the same physical size as your GP-30 with the addition of a colour display:
http://www.furuno.co.uk/dealers.php5
If you feel we can be of any further assistance then please ask and I will endeavour to try my best and answer any questions that you may have.
neil_s
Well-known member
I did switch on my GP-30 just before Christmas. Although the date was incorrect, the position agreed perfectly with the GPS mouse on my laptop. I have been 'rolled over' for some years, now!